# . Stage 1 Components

## 5.1 Magnets {#magnets .unnumbered}

### 5.1.1 Introduction {#introduction .unnumbered}

The magnet system of the 20 TeV Stage-I VLHC is the main component of
the collider, and has a strong influence on the total cost of machine.
The general design goal is to reduce the complexity and cost per
Tesla-meter of the collider. The arcs of the Stage 1 VLHC are based on a
2-in-1 warm-iron, combined function gradient dipole magnet\[1-3\] which
is excited by a single turn 100 kA superconducting transmission line. A
cross-section of the magnet, including the cryogenic service line and
return bus, is shown in Figure 5.1. The flux lines surrounding the
transmission line are shaped by an iron yoke, and two gaps in the yoke
provide the apertures for the two beams. The 20 TeV bending field is
1.966 T at the nominal current of 87.5 kA. The magnets have a field
gradient of ±4.73%/c, which provides focusing and eliminates the need
for separate quadrupoles. The 135.5 m long half-cell is made of two
65.75 m long gradient magnets.

![](media/image1.wmf){width="5.986805555555556in" height="4.58125in"}

Figure 5.1. Cross-section of the gradient dipole magnet used in the arcs
and dispersion suppressor of the Stage-1 VLHC.

At the end of each half-cell, where the beta function is maximum in one
plane and minimum in the other, a 3.5 m long space is left open for
correction coils. The transmission line is diverted into the cryogenic
service pipe, near the return bus, allowing the use of conventional,
room temperature, air cooled iron corrector magnets, as shown in Figure
5.2. Three correctors are installed at each location: a vertically or
horizontally steering dipole, a quadrupole and a sextupole corrector.
The strength of these correctors is sufficient toeaccommodate alignment
errors, ground motion, and iron saturation effects at full field
(section 3.2).

![](media/image2.wmf){width="6.645138888888889in"
height="3.354861111111111in"}

Figure 5.2. Correction coils placed at each half-cell boundary (135m
spacing).

The dispersion suppressor sections are similar. Here the 101.6 m long
half-cell is made of two 48.81 m long dipoles with correctors. The
gradient is increased to ±9.449 %/cm and the bend field reduced to 1.766
T to match the footprint of the Stage 2 machine (see sect. 3.1.2).

Conventional water cooled quadrupoles are used in the straight sections.
Two 6.1 m long, 70 T/m quadrupoles are used in a typical 135 m
half-cell. Special optics for the machine utilities -- injection, abort,
the RF system, beam cleaning, and the matching sections of the
interaction regions are constructed using quadrupoles of the same design
but with special lengths. The low-beta triplets utilize superconducting
300 T/m cos2θ quadrupoles made from Nb~3~Sn cable. Special dipole
magnets, similar in concept to the arc gradient magnets and excited by
the transmission line, are used to bring the beams into collision at the
interaction regions, to separate the beams to make room for RF cavities,
and at the beam cross-over regions.

Table 5.1 summarizes the main parameters of the magnets used in the
VLHC-1 design.

Table 5.1. Main parameters of magnets in the Stage-1 VLHC.

+---------------+-------+-------+-------+-------+------------------+
| Magnet Type   | B     | G     | L     | N     | Notes            |
|               | ~nom~ | ~nom~ | ~mag~ | umber |                  |
|               | (T)   | (T/m) | (m)   | of    |                  |
|               |       |       |       | ele   |                  |
|               |       |       |       | ments |                  |
+---------------+-------+-------+-------+-------+------------------+
| Gradient      | 1.97  | 9.73  | 65.75 | 3136  | Main Arc Magnets |
| dipole (arc)  |       |       |       |       |                  |
+---------------+-------+-------+-------+-------+------------------+
| Gradient      | 1.80  | 16.88 | 48.81 | 160   | Dispersion       |
| dipole (DS)   |       |       |       |       | Suppressors      |
+---------------+-------+-------+-------+-------+------------------+
| Straight sect |       | 70    | 4.8 - | 464   | room temp.       |
| quads         |       |       | 6.8   |       | conventional     |
+---------------+-------+-------+-------+-------+------------------+
| Low β         |       | 300   | 9.2 - | 8     | Supercond. IR    |
| quadrupoles   |       |       | 10.9  |       | Quads            |
+---------------+-------+-------+-------+-------+------------------+
| Special       | 1.95  |       | 25 -  | 52    | Separation,      |
| dipoles       |       |       | 35    |       | recombination,   |
|               |       |       |       |       | and cross-over   |
+---------------+-------+-------+-------+-------+------------------+
| Correctors    |       |       |       |       | Air-cooled       |
|               |       |       |       |       | Iron/Copper      |
+---------------+-------+-------+-------+-------+------------------+
| > Dipole      | 1.0   |       | 0.50  | 1648  | Every "F"        |
| > (horiz.)    |       |       |       |       | location         |
+---------------+-------+-------+-------+-------+------------------+
| > Dipole      | 1.0   |       | 0.50  | 1648  | Every "D"        |
| > (vert.)     |       |       |       |       | location         |
+---------------+-------+-------+-------+-------+------------------+
| > Quadrupole  |       | 25    | 0.50  | 3296  | Every F&D        |
|               |       |       |       |       | location         |
+---------------+-------+-------+-------+-------+------------------+
| > Sextupole   |       | 1750  | 0.80  | 3296  | Every F&D        |
|               |       | T     |       |       | Location         |
|               |       | /m^2^ |       |       |                  |
+---------------+-------+-------+-------+-------+------------------+

During the past three years, most of the R&D effort has concentrated on
the dipole design, with considerable attention focused on the 100 kA
superconducting transmission line cable and cryogenic system. Conductors
meeting all requirements have been developed and successfully tested at
a 17m length 100kA superconducting test stand \[4\]. This design study
uses cables and splicing methods identical to those tested. A low
heat-leak cold mass shielded support system was developed (sect
5.1.2.2). A 100kA power supply and current leads (Figure 5.41) are being
built for extended system tests. A 50m Invar pipe was thermally cycled
1000 times to verify cryogenic weld reliability in the
"zero-contraction" mode \[9\]. The parameters of the cryogenic system
including pipe sizes, pressure drops, and refrigeration process flows
have been calculated. Quench behavior has been calculated with a
detailed magneto-hydrodynamic simulation \[8\] and results were in
adequate agreement with observations in the 17m test loop. The magnetic
and mechanical design was refined and several configurations tested
using a room temperature magnetic test stand \[5\]. Two 6 m magnet
prototypes with the parameters of this design study are now being
manufactured to confirm the main technical decisions.

Section 5.1.2 describes the combined function arc and dispersion
suppressor magnets in detail, including magnetic design, design of the
100 kA transmission line, and the mechanical and thermal designs. The
correctors are described in section 5.1.3 and the interaction region
magnets in section 5.1.4. Section 5.1.5 presents the various special
magnets, including straight section quadrupoles; beam separation,
recombination and cross-over dipoles; and injection and abort system
magnets. Production of the 66 m long gradient dipoles and the testing
and measuring of them are described in sections 5.1.6 and 5.1.7
respectively. Transport, installation and alignment methods are
summarized in section 5.1.8.

### 5.1.2 Combined function Arc Magnets {#combined-function-arc-magnets .unnumbered}

The twin-aperture superconducting transmission line magnets \[1-7\] are
shown in Figures 5.1 and 2.6. All bending magnets share a common single
turn excitation transmission line winding. The return bus, located
within the cryogenic service pipe, is 290 mm below the drive bus. There
are several advantages of this the single turn warm iron magnet: simple
construction, low parts cost, low inductance, small cold mass, low field
in the superconductor area, absence of turn to turn insulation, low
magnetic forces and heat leak, high stability against beam losses and
simple quench protection. Nevertheless there are some negative effects
associated with the external return bus: a non-negligible fringe field,
asymmetric saturation of the lower and upper iron half-cores, and
partially uncompensated magnetic forces on the drive and return busses.

Table 5.2 shows the main parameters of the dipole magnets. Section
5.1.2.1 describes the magnetic design. The transmission line design is
presented in section 5.1.2.2. The mechanical and thermal designs are
described in section 5.1.2.3, including the magnet structure, the
transmission line, the cryogenic service pipe and cryostat, and the beam
pipe. The magnet ends, where space is provided for the correction
magnets and interconnections from one magnet to the next are made, is
described in section 5.1.2.4.

####  {#section .unnumbered}

####  {#section-1 .unnumbered}

#### Table 5.2. Main Parameters of Dipole Magnets {#table-5.2.-main-parameters-of-dipole-magnets .unnumbered}

  ----------------- ------------ ---------------------- -------------------
                                 *Main Arc Dipole*      *Dispersion
                                                        Suppressor*

  Magnet air gap in              20 mm                  22.26 mm
  the orbit center                                      

  Beam Pipe Inner                18 mm x 28 mm          
  Dimensions                     (elliptical)           

  Separation                     150 mm                 
  Between Beams                                         

  Magnet length                  65.74 m                48.81 m

  Half-cell length               135.5 m                101.6 m

  Gradient                       ± 4.73 %/cm            ± 9.449%/cm

  Magnetic field:   injection    0.1 T                  0.09 T

                    maximum      1.966 T                1.766 T

  Good field        injection    20 mm                  
  diameter (\<                                          
  0.02%):                                               

                    maximum      10mm                   

  Transmission Line              100 kA                 
  Design Current                                        

  Current at 20 TeV              87.5 kA                

  Magnetic field                 790 kJ (12kJ/m)        473 kJ (10kJ/m)
  energy \@100kA                                        

  Superconducting                Braided NbTi with      
  cable                          Braided Cu Stabilizer  

  Specified Max.                 6.5-6.7 K              
  Temp of Conductor                                     

  Nominal Max Temp               6.0 K                  
  of Cryo System                                        

  Iron Core                      1 mm Laminated low     
                                 carbon Steel (AISI     
                                 1008 or better)        
  ----------------- ------------ ---------------------- -------------------

Figure 5.3 shows a detailed cross-section of the magnet, with an inset
showing the dimensions and placement of the saturation control holes.
The laminated core consists of upper and lower iron half cores, which
are stamped from 1 mm thick low carbon steel. The upper and lower
laminations are stacked and welded into 6 m long yoke blocks, which are
then assembled into the complete yoke structure. The precise spacing
between the two yoke halves is set by non-magnetic 316L stainless steel
spacer bars, and the two halves are welded together with non-magnetic
steel plates at the inner radius. The weld is done inside a press, and
the weld shrinkage provides the preload necessary to assure precise and
stable contact between all of the laminations and the spacer bar. The
yoke blocks are mounted on the support tube which also serves as the
cryogenic service pipe for the magnet. Yoke and support tubes assemblies
12m long are shipped to Fermilab from outside vendors. Final assembly
into 65m magnets, including insertion of the transmission line cryostat,
beam pipes, and cryo service pipes, is performed in final assembly
buildings on site as described in section 5.1.6.

![](media/image3.wmf){width="5.986805555555556in"
height="3.982638888888889in"}

Figure 5.3. Cross-section of transmission line magnet yoke. Inset shows
holes used to control field defects from iron saturation.

#### 5.1.2.1 Magnetic design {#magnetic-design .unnumbered}

The combined function gradient dipole is an iron-dominated magnet, in
which the field quality is determined mainly by the shape of the pole
tips and the properties of the iron from which they are made. The field
quality is insensitive to conductor placement errors as large as 1mm.
The magnet must maintain a high quality field over a 20:1 dynamic range.

![](media/image4.wmf){width="4.151388888888889in"
height="2.6104166666666666in"}

Figure 5.4. Magnetic field strength as a function of transmission line
current. The 20 TeV bend field of 1.966 Tesla occurs at 87.5kA. The
design current of the transmission line is 100kA.

##### Field Quality at Injection {#field-quality-at-injection .unnumbered}

Field quality requirements are most severe at injection where the beams
are largest. The injection field of 0.1 T is above the range where
hysteretic field defects cause difficulties. Recent experience building
several hundred iron magnets for the Fermilab Main Injector and Recycler
projects has shown that achieving the required 10^-4^ field quality in
production is straightforward at this field level.

Mechanical tolerances on the pole tip shape will be tighter for the 2 cm
magnet gap of the VLHC than for magnets with larger gaps. (Field error
modeling is discussed in 3.2.2.) Relatively thin 1mm steel laminations
are chosen to improve this tolerance. If necessary, end shimming
techniques similar to those used in Recycler production \[10\] can be
used to reduce systematic and random multipoles at injection to a level
limited by magnet measurement errors. Finally, a technique has been
tested to put inexpensive multipole correctors in the body of the
magnets by running wires down the saturation-control holes in the pole
laminations \[11\]. It is unlikely that these will be needed.

##### Saturation Control and Maximum Dipole Field {#saturation-control-and-maximum-dipole-field .unnumbered}

The main design challenge is dealing with field distortions induced by
saturation of the iron at fields from 1.7 to 2 T. Both sextupole and
gradient shift are important. The sextupole defect is caused by early
saturation of the corners of the pole tips, since they carry more flux
than the centers of the pole. Gradient shifts are caused by asymmetric
saturation on the high-field (narrow gap) side of the gradient magnet.
Both of these saturation effects are controlled in the current design
with a set of holes placed in the iron near the poles (see Figure 5.3
inset). At the highest fields where the holes are insufficient,
quadrupole and sextupole corrector magnets in each halfcell are needed
to regulate tune and chromaticity.

There is a tradeoff between the maximum bend field (beam energy) and the
strength of the corrector system required to compensate saturation
effects. The present system allocates 1.2% of the ring circumference to
sextupole and gradient corrector magnets. These allow a peak field \~15%
higher than would be possible without these strong correctors. This
seems worthwhile even given the larger cost-per-meter of the corrector
magnets. On the other hand, doubling the current corrector strengths
would increase the peak field by less than 5% (see Figure 5.6). Thus the
chosen correctorsstrengths seem to be roughly optimized.

Field quality optimization with "holes in the poles" proceeds as
follows. Best results are obtained with a large number of holes, whereas
field strength and mechanical considerations favor a smaller number of
holes. The combined optimum was found to be three holes per pole, as
shown in Figure 5.3. The field optimization objective function was the
integral field homogeneity around a circular aperture. The optimization
process was carried out simultaneously for three field levels (1 T, 1.7
T and 2.0 T). The optimization was done using an ANSYS Subproblem
Optimizer, and a large number of local minima were investigated. The
best solution was tested by OPERA 2D and had ±0.02% field quality within
a 20 mm diameter aperture for 0.1 ≤ B ≤ 0.8 T, 15 mm for 0.8 \< B ≤ 1.5
T, and 10 mm for 1.5 T \< B \< 2.0 T. This shrinkage of good field
region is acceptable since the beam is \~4x smaller at full energy than
at injection.

Both the Main Arc and Dispersion Suppressor magnets are excited by the
common transmission line. The Dispersion Suppressor magnets operate at a
higher gradient and reduced bend field to match the footprint of the
Stage 2 dispersion suppressors. This results in similar pole tip fields
and saturation characteristics for both magnet types.

We have not re-optimized the pole tip designs for the current design
study parameters. The results shown below \[6\] correspond to an earlier
parameter set with a smaller gradient of ±3%/cm, corresponding to a
lattice with 60°/cell phase advance and 150m halfcell length, and a
smaller spacing of 140 mm between beam apertures than the current value
of 150 mm. It is anticipated that performance similar to that described
here will be achieved for the current designs when their optimization is
complete.

Figure 5.5 shows the effects of putting the correction holes in the pole
laminations on the saturation sextupole at 1.8 T. The measured results
agree well with the 2-D calculation, and demonstrate a large improvement
with respect to the field shape without holes. Figure 5.6 compares the
calculated and measured shift in the quadrupole moment as a function of
excitation for a prototype yoke stack. The quadrupole and sextupole
errors are ±2 units in the field range 0.1T - 1.85T and both are about
-8 units at 1.95T.

![](media/image5.wmf){width="6.221527777777778in"
height="4.367361111111111in"}

Figure 5.5. Measured effect of "Holes in the Poles" on the Saturation
Sextupole as a function of transverse position in the Transmission Line
Magnet

![](media/image6.wmf){width="5.738888888888889in"
height="4.373611111111111in"}

Figure 5.6. Effect of "Holes in the Poles" on the Gradient Shift in the
Transmission Line Magnet

##### Magnetic Forces and Asymmetric Saturation {#magnetic-forces-and-asymmetric-saturation .unnumbered}

In order to suppress distant magnetic fringe fields and minimize the
system inductance, a return conductor is placed outside the magnet
laminations. At the mid point of the accelerator, the drive conductor
returns back through the first half of the magnets (but outside the
lamination stack). At the points where the beams cross each other -- at
the interaction regions and the beam cross-over insertions -- the drive
and return busses trade places. See Figure 5.39.

The drive conductor is centered in the iron yoke and the return
conductor is placed 290 mm below the drive conductor. The return
conductor generates a fringing field which saturates the lower core more
than the upper, which decreases the field quality in the gaps and
increases the magnetic force on the drive conductor. This can be
countered by increasing the thickness of the lower half core and
adjusting the spacing of the return conductor. With these two adjustable
parameters it is possible to adjust the magnetic force to zero on both
the drive and return conductors when they are at their nominal position
at full current. This same optimization largely eliminates the
asymmetric (skew) multipoles in the magnet gap.

Although the force on the drive conductor in its nominal position is
zero, it experiences a force gradient of about 200 kg per meter of
magnet per mm of displacement. The force is horizontally stabilizing and
vertically destabilizing (negative spring constant). The force gradient
on the return conductor is 20 times smaller. The mechanical implications
of this are discussed in section 5.1.3.

5.1.2.2 Superconducting Transmission Line

The transmission line consists of a cylindrical superconducting braid
inside a pipe cooled by supercritical 4.5-6.0 K helium, which is placed
inside a co-axial cryostat, which in turn is placed at the center of the
room temperature iron yoke. A three dimensional view of a drive
conductor transmission line is shown in Figure 5.7. The transmission
line consists of (from inside out) a 2.5cm helium flow space, a
perforatedIinvar tube, a copper stabilizer braid, the braided
superconductor cablf, an Invar pipe to contain the helium, the cold pipe
support, a cryoshield, the superinsulation blanket, and the vacuum
jacket. The cold pipe suppors centers the conductor cabltoin the vacuum
jacket which in turn is placed centrally inside the magnet lamination.
It also supports the cryoshield pipe which in turn supports the
superinsulation blanket.

![](media/image7.jpeg){width="5.6in" height="4.159027777777778in"}

Figure 5.7. A 3D view of the drive conductor transmission line.

The main design requirements for the transmission line are as follows.
First, it must contain enough superconductor to carry the specified
current of 100kA at 6.5K. This includes a significant margin since the
peak temperature cryogenic system is specified at 6.0K (section 5.2.1)
and the required current for 20 TeV is 87.5kA. It must maintain a 2.5cm
clear bore for the helium flow in a 10km loop. It must contain enough
copper stabilizer and thermal mass to carry the full current in the
non-superconducting state during a 1 second shutdown following a quench.
The cold pipe must handle the maximum pressure transient of \~35 Bar
which occurs during a quench. The cold mass supports must center the
conductor with an accuracy of 0.5mm and resist magnetic decentering
forces while maintaining a low heat leak consistent with the cryogenic
design. Finally, it must survive hundreds of temperature cycles *with
its ends constrained*, since the transmission line forms a loop around
the accelerator which can not be allowed to shrink during cool down.
This mandates the use of Invar (36% Nickel steel) for the cold pipes.

##### Conductor Designs {#conductor-designs .unnumbered}

Three distinct conductor designs are utilized (see Table 5.3). The main
drive bus that excites the dipole is optimized for minimum size
consistent with operation at 100 kA in a \~1 T self-field. The current
return bus in the cryogenic service pipe is identical to the drive bus
but enlarged to increase flow area. A special type of conductor is
required at the half-cell boundaries where the drive conductor is
diverted downward to make space for the correction magnets (see Figure
5.2).

Table 5.3. Main parameters of the three types of transmission line
conductors.

+-----------------+-------------+-----------------+-------------------+
|                 | > **Drive   | > **Return      | > **Bus in Corr.  |
|                 | > Bus**     | > Bus**         | > Space**         |
+-----------------+-------------+-----------------+-------------------+
| > Cu/SC ratio   | > 1.8       | > 1.8           | > 1.3             |
+-----------------+-------------+-----------------+-------------------+
| > Diameter (mm) | > 0.648     | > 0.648         | > 0.808           |
+-----------------+-------------+-----------------+-------------------+
| > Cond. Type    | > Braid     | > Braid         | > 9 Rutherford    |
|                 |             |                 | > Cables          |
+-----------------+-------------+-----------------+-------------------+
| > Number of     | > 288       | > 288           | > 270             |
| > strands       |             |                 |                   |
+-----------------+-------------+-----------------+-------------------+
| > Cu Wire dia.  | > 0.64      | > 0.64          | > 0.64            |
| > (mm)          |             |                 |                   |
+-----------------+-------------+-----------------+-------------------+
| > Number of     | > 240       | > 288           | > 288             |
| > wires         |             |                 |                   |
+-----------------+-------------+-----------------+-------------------+
| > Inner Pipe ID | > 25.3      | > 36.8          | > 36.8            |
| > .(mm)         |             |                 |                   |
+-----------------+-------------+-----------------+-------------------+
| > Outer Pipe OD | > 38.1      | > 47.1          | > 50.1            |
| > (mm)          |             |                 |                   |
+-----------------+-------------+-----------------+-------------------+
| > Max working   | > 40        | > 40            | > 40              |
| > Pressure      |             |                 |                   |
| > (bar)         |             |                 |                   |
+-----------------+-------------+-----------------+-------------------+

A braided conductor is used for the main drive and return buses. The
superconductor braids are sandwiched between an inner perforated Invar
pipe, which serves as a liquid helium channel, and an outer Invar
pressure pipe which closes the helium space. The braid consists of 288
NbTi strands arranged in a pattern of two sets of 24 crossing bundles
with opposite pitch angle about the tube. It uses strands of the
dimension of the SSC dipole outer layer design and current prototypes
use actual SSC strand. For VLHC-1 it is planned to use a more cost
effective wire optimized for the lower fields seen here and without the
constraint of small filament size. There is also a copper braid placed
inside the superconductor that provides an additional copper for
carrying current during a quench. The conductor braid is secured in
position by swaging the inner pipe against the outer one by drawing a
series of carbide steel balls through the pipe. This provides adequate
clamping and preload against the radial compressive forces of the
magnetic self-fields, as evidenced by the fact that all of our test
cables built this way achieved \~100% of the theoretical current at
quench.

The bus in the 3.5m long corrector magnet region uses a spiral wrap of 9
SSC inner dipole Rutherford cables in place of the braid. Here, due to
the proximity of the two currents, the peak field rises to 1.5 T,
requiring more superconductor to carry the 100 kA current. Cables are
used here rather than braid to allow openings to be made for in the
superconductor assembly for pressure relief ports, which are placed at
every 4th half-cell (542 m). The Rutherford cables have less void space
which may help reduce conductor motion in the presence of azimuthal
forces in this region.

Both types of conductors (and the 10cm long splice between them) have
been successfully tested in the 100kA test facility. Splice power
dissipation was \<0.2W at 100kA.

A cross-section of the drive conductor cryostat is shown in Figure 5.8.
The support spider consists and injection molded ULTEM ring with two
pairs of pegs pointing up and down, the direction of the magnetic force.
The inner pair of pegs support the cold pipe, while the outer pegs
contact the vacuum shell. The conductor must be placed precisely on the
central line of the magnet to minimize the de-centering force. Offsets
of the order of 0.5 mm, in excess of what can be expected due to part
tolerances, lead to de-centering forces on the order of 100 kg/m. The
supports must withstand 100,000 mechanical cycles during the accelerator
lifetime. Laboratory tests these supports withstood 100,000 mechanical
cycles of 300 kg/m force, three times that of the design requirement.
Further design development, however, may be required to optimize the
spider design with respect to axial motion, expected under thermal
cycling. (See section 5.1.2.3.)

> ![](media/image9.wmf){width="6.145138888888889in"
> height="3.834722222222222in"}

Figure 5.8. The details of the drive conductor cryostat.

The cryo-shield is made of extruded aluminum pipe segments \~50 cm long,
which slide over opposite ends of each support spider. The 6.4 mm
diameter invar pipe that is used to provide the 50 K pressurized helium
is "snapped in" to the cavities at the top and the bottom of both the
shield and the supports once a magnet's length of shield has been
assembled. The shield pipe is wrapped with 40 layers of a dimpled
superinsulation blanket. The vacuum jacket is made of extruded aluminum,
and it is of a "squared" shape to firmly fix its position inside the
iron laminations. This also helps to prevent potential rotation (and/or
twist) of the cold pipe supports.

The critical temperature vs. current for the braided conductor is shown
in Figure 5.9. The data point is the measured performance of the
conductor used in the prototype, and the diagonal line is the computed
performance using the properties of NbTi and the self-field as a
function of current. The slope of this line was measured on other
transmission line samples and agrees with theory. At 90 kA current the
critical temperatures is 6.8 K. The temperature margin of 0.7 K with
respect to the maximum helium temperature of 6.1 K (see Section 5.2.1)
is sufficient both for stability of the superconductor and for
operational "head room." The margin for the braided conductor,
normalized to its higher self-field in the space between dipoles, is
slightly larger than for the main conductor.

![](media/image10.wmf){width="5.354861111111111in"
height="3.3854166666666665in"}

Figure 5.9. The critical temperature vs. current for main drive and
return conductors.

The quench propagation velocities were measured in a 17 m long conductor
loop\[4\]. It was found that in a forced quench by a local heating of
\~10 K, quench propagation velocity rises linearly with current, and it
reaches about (10-12) m/s value at \~80 kA. Above this current, it rises
exponentially reaching about (30-40) m/s value at 100 kA. This indicates
that by applying a current dump circuit of a time constant of 1 s, the
stored magnetic energy released in a quench would be at most that of a
half length of a dipole magnet (34 m), thus not exceeding 1 MJ value.

**THIS QUENCH DISCUSSION STILL NEEEDS WORK**

Detailed thermohydraulic simulations have also been performed on many
quench scenarios with a number of different configurations of the
transmission line. The simulations use a 1 V quench detection threshold
and a 1 second decay time constant (see Section 5.2.2.3). The
calculations demonstrate that, for conceivable worst-case scenarios, the
peak temperature remains low (\<60 K) and, with relief valves spaced
every four half-cells, the peak pressure is below the 40 bar maximum for
which the invar pipe is rated without taking credit for the increased
strength at low temperature. The simulations also show that the
additional copper stabilizer braid is essential. Without it the peak
temperature can reach 250 K, and the higher temperature can result in
peak pressure above 40 bar.

#### References {ed. note -- for Secs 5.1.0 -- 5.1.2.2} {#references-ed.-note-for-secs-5.1.0-5.1.2.2 .unnumbered}

**\[GW FOSTER STILL NEEDS TO LOOK OVER THESE REFERENCES\]**

\[1\] R.R. Wilson, Proceedings of Snowmass 1982.

\[2\] "The Pipetron: a Low-Field Approach to a Very Large Hadron
Collider," Snowmass '96.

\[3\] G.W.Foster, "Transmission Line Magnet Status Report", VLHC
Information Packet for HEPAP Subpanel, Fermilab 1998.

\[4\] G.W.Foster, V.S.Kashikhin, E.Malamud, P.Mazur, H.Piekarz,
J.Fuerst, R.Rabehl, P.Schlabach, J.Volk, "The 100 kA VLHC Transmission
Line Magnet Superconducting Cable Test Facility," MT-16, IEEE Trans. of
Applied Superconductivity, Vol.10, No.1, March 2000, pp.318-321.

\[5\] J.DiMarco, G.W.Foster, V.Kashikhin, A.Makarov, P.Schlabach,
"Measurements of a Crenellated Iron Pole Tip for the VLHC Transmission
Line Magnet," PAC 99, pp. 3327 -- 3329.

\[6\] G.W.Foster, V.S.Kashikhin, I.Novitski, "Design of a 2 Tesla
Transmission Line Magnet for the VLHC," MT-16, IEEE Trans. of Applied
Superconductivity, Vol.10, No.1,March 2000, pp.202-205.

\[7\] G.W. Foster, V.S.Kashikhin, V.V.Kashikhin, "Pole Profile
Optimization of VLHC Transmission Line Magnet," EPAC 98.

\[8\] Quench simulation final report \[TD note #?\]

\[9\] Ron Walker, 50m Invar Thermal Cycling Report

\[10\] GWF EPAC '98 talk & other Recycler shim talks

\[11\] Kashikhin write-up on corrector wires in holes-in-the-poles.

5.1.2.3 Mechanical and Thermal Design

##### 5.1.2.3.1 Magnet Mechanical Structure {#magnet-mechanical-structure .unnumbered}

###### Magnet Length {#magnet-length .unnumbered}

Many considerations entered into the 67.75 m magnet length chosen for
this study. There appear to be no hard technological or financial limits
to considering magnets either twice as long or half as long. The weight
of 33 tonnes is slightly less that an LHC dipole so that considerations
of floor loading, transportation power, etc. will be comparable. A
magnet of this length can be picked up by two points and transported
using a lifting fixture (load spreader bar) which weighs 1/3 as much as
the magnet and is small enough (2m height) to fit into the tunnel. This
greatly simplifies handling. All instrumentation and cables can be
factory-installed and tested on our ¼ cell long magnets, but this is not
true of shorter magnets. Cryogenic heat load from transmission line
splices is about 0.4W per magnet end or \<10% of the total 5K heat load.
Labor estimated for tunnel splicing is \~60 person-hours per magnet end
which corresponds to \<\$10M for 3000 magnets. This sets the scale for
possible savings of in-tunnel labor from longer magnets. Doubling the
magnet length would increase the floor space of the factory by about
50%.

######  Distance Between Support Posts and Gravitational Sag  {#distance-between-support-posts-and-gravitational-sag .unnumbered}

The main structural element of the magnet assembly is the 300 mm steel
pipe which serves the vacuum jacket for the cryogenic service lines and
current return. The magnet cores act mainly as a dead weight on this
pipe. The support pipe is made from A36 carbon steel 5mm thick. The
magnet core is welded to the tube every 0.5 m to increase the vertical
stiffness of the assembly and to reduce system deflection.

######  {#section-2 .unnumbered}

######  {#section-3 .unnumbered}

######  {#section-4 .unnumbered}

######  {#section-5 .unnumbered}

###### The magnet is installed on vertical supports every 6 m. This distance was chosen \[1\] to limit deflections due to gravity to 1-- 2 mm depending on assumptions about the connections between the cores and service pipe. As is common for long laminated magnets, this deflection will be precompensated by assembly tooling so the magnet sags into alignment. The present design also allows for a final shimming of the core position if needed. The maximal stresses does not exceed 50 -- 60 MPa.  {#the-magnet-is-installed-on-vertical-supports-every-6-m.-this-distance-was-chosen-1-to-limit-deflections-due-to-gravity-to-1-2-mm-depending-on-assumptions-about-the-connections-between-the-cores-and-service-pipe.-as-is-common-for-long-laminated-magnets-this-deflection-will-be-precompensated-by-assembly-tooling-so-the-magnet-sags-into-alignment.-the-present-design-also-allows-for-a-final-shimming-of-the-core-position-if-needed.-the-maximal-stresses-does-not-exceed-50-60-mpa. .unnumbered}

###### Force to Introduce Sagitta and Alignment Bumps {#force-to-introduce-sagitta-and-alignment-bumps .unnumbered}

**GWF DOES NOT UNDERSTAND THE NUMBERS IN THIS PARAGRAPH**

The magnet horizontal sagitta is \~15 mm over its 67 m length. To
estimate deformations of the straight magnet structure introduced by
this sag during alignment in the tunnel, numerical 3D simulations were
performing using a 12-m section model \[2\]. Over such a distance the
sag is \~0.5 mm. Both model ends were restricted from motion. The model
with a distributed weight was loaded by horizontal force applied to the
central supports of the vacuum tube. The result shows the magnet block
moves about 0.9 mm for 1 mm movement of the vacuum tube. The force
needed for 1 mm motion is 450 kg. Difference in relative movement of the
iron halves of the magnet can reach 30 μm.

Yoke Deflection and Gap Stability under Magnetic Forces

The magnetic force acting between the yokes rises quadratically from
6 kg/m at injection to 2500 kg/m at the maximum field of 2 T. The
outside of the gaps must remain open for magnetic measurements and
vacuum chamber installation. Thus this force is taken across support
spacers in the relatively small \~1 cm distance between the transmission
line vacuum jacket and the beam pipe. The yoke and gap spacer assembly
must be rigid enough to keep the air gap stable within \~20μm. Several
prototypes were built before identifying a viable and economic design.

The laminated magnet yoke (Figure 5.3) consists of upper and lower iron
half cores. Core laminations are stamped from 1 mm thick low carbon
steel. The stack of laminations is pressed and welded into a block. Two
blocks, upper and lower, separated by two nonmagnetic 316L stainless
steel spacer bars and are welded together by stainless steel strips from
the inside of the central hole. The weld contraction provides a preload
greater than 5 tons/m which removes all clearances between the spacer
bars and half-cores.

Tests of the final short mechanical model showed that under full load
the left gap shrank vertically by 12 μm and the right gap by 6 μm. The
horizontal change was less than 4 μm. These changes were reproducible
indicating elastic deformation. In full magnetic testing a 1 m model
with outer spacer bars was successfully tested and no gradient shift was
observed (Figure 5.6) aside from that expected from iron saturation
\[4\]. These measurements will be repeated with better statistics on
longer magnets currently in production.

###### 5.1.2.3.2 Magnetic Forces on the Transmission Line and Cold-Mass Support Spider {#magnetic-forces-on-the-transmission-line-and-cold-mass-support-spider .unnumbered}

######  {#section-6 .unnumbered}

######  {#section-7 .unnumbered}

Loads from transmission line magnetic forces are transmitted from the
drive conductor to the pipe, through the supports (spiders) to the
vacuum jacket, and to the magnet core. In the ideal case, the magnetic
forces are zero on both the drive and return conductors as described in
section 5.1.2.1. Nevertheless, iron saturation effects and assembly
tolerances in the position of superconducting cable will cause
uncompensated magnetic forces \[3\]. At a current of 100kA, each meter
of the transmission line experiences a decentering force gradient of 228
kg per mm of vertical displacement and a stabilizing force gradient of
100 kg/mm in the horizontal direction.

  -------------- -------- -------- --------- ---------- -------- ----------
                                                                 

                                                                 

                                                                 

                                                                 
  -------------- -------- -------- --------- ---------- -------- ----------

If the steel pipes will be equipped with compensation bellows every \~33
m to reduce shrinkage to the level of \~100 mm, the convoluted length of
the bellow is 100/0.25 = 400 mm. The force to expand the bellows by 50
mm is 300 kg for the bellows' spring constant 6 kg/mm. The bellows'
stability problem is solved by using the internal tube liner and the
outer protecting skin.

######  {#section-8 .unnumbered}

######  {#section-9 .unnumbered}

###### The vertical force gradient gives rise to an instability \[5\] in which the current-carrying pipe bends into a sinuous curve with a period of twice the support distance. This instability sets the maximum support interval of 0.5 m. {#the-vertical-force-gradient-gives-rise-to-an-instability-5-in-which-the-current-carrying-pipe-bends-into-a-sinuous-curve-with-a-period-of-twice-the-support-distance.-this-instability-sets-the-maximum-support-interval-of-0.5-m. .unnumbered}

Spiders made of ULTEM \[18\] centrally position the conductor. If
perfectly positioned, pegs are under pure compression inside the
cryostat. The compression depends on the leg over-sizing and on the
variation in pipe diameter. A 0.5 mm tolerance is required on the
roundness of both pipes. The pressure range is 20-40 kg. These numbers
increase up to 70-100 kg at cold conditions and under action of magnetic
force.

Prototype injection-molded supports were exposed to 100,000 mechanical
cycles with a load force of 300 kg/m (three times that expected) \[19\].
This test indicates that in principle the transmission line supports
would function with every second spider missing or destroyed.

The relative axial motion of the cold conductor line and the warm vacuum
jacket tube requires the spiders to slide along the pipes to avoid a
high stress in the spider material \[6\]. The sliding behavior needs to
be carefully verified in system tests. If it is insufficient, alternate
rolling or sliding support systems can be used \[7,8,9\].

  ---------------------------- --------- -------------------------- -------
                                                                    

                                                                    

                                                                    

                                                                    

                                                                    

                                                                    
  ---------------------------- --------- -------------------------- -------

  ---------------------------- --------- -------------------------- -------
                                                                    

                                                                    

                                                                    

                                                                    

                                                                    

                                                                    

                                                                    
  ---------------------------- --------- -------------------------- -------

###### Magnetic Forces on Current Return Conductor  {#magnetic-forces-on-current-return-conductor .unnumbered}

The return conductor is at a force null in the main body of the magnet,
and experiences a force gradient 20 times smaller than the drive
conductor. However in the corrector region where the busses are not
shielded from each other, the magnetic forces are 700 kg/m at the
standard separation of 0.29 m, increasing to \~4000 kg/m at the 10 mm
separation in the corrector region. This force is handled by
mechanically connecting the two busses together in this region with an
insulating cold-to-cold support that does not generate a heat leak.

##### 5.1.2.3.2 Longitudinal forces, Interconnects, Pipes, and Bellows  {#longitudinal-forces-interconnects-pipes-and-bellows .unnumbered}

###### Longitudinal Forces from Thermal Contraction of Invar Pipes {#longitudinal-forces-from-thermal-contraction-of-invar-pipes .unnumbered}

The conductors in the transmission line magnet form a continuous loop
around the ring circumference which cannot be allowed to contract as the
pipes cool down. Expansion bellows can be used for normal cryogenic
piping but not with the transmission line conductor. The best solution
is to use materials such as Invar which will go into tension but not be
destroyed as they are cooled down with their ends constrained.

Table 5.4. Stress in pipe materials after cool down from 300 K to 5K
with ends constrained

+----------------+------+-------+--------+---------+-------+--------+
| ##### Mate     | *∫α  | *E    | *σ=E\  | *       | *σyie | *∆     |
| rial {#materia | dt,* | (5K)* | *∫αdt* | σyield* | ld/σ* | L(mm)* |
| l .unnumbered} |      |       |        |         |       |        |
|                | *m   | *GPa* | *MPa*  | *MPa*   |       | *L     |
|                | m/m* |       |        |         |       | =135m* |
+----------------+------+-------+--------+---------+-------+--------+
| > 304          | 3    | 220   | 660    | 6       | 0.    | 405.0  |
| > Stainless    |      |       |        | 00-1200 | 9-1.8 |        |
| > Steel        |      |       |        |         |       |        |
+----------------+------+-------+--------+---------+-------+--------+
| > 6061         | 4.1  | 80    | 328    | 380     | 1.15  | 553.5  |
| > Aluminum     |      |       |        |         |       |        |
+----------------+------+-------+--------+---------+-------+--------+
| > Invar (36%   | 0.48 | 140   | 67     | 7       | 10.4  | 64.8   |
| > Ni Steel)    |      |       |        | 00-1000 | -14.9 |        |
+----------------+------+-------+--------+---------+-------+--------+

As the table above indicates, Invar will survive cooldown with 67 MPa of
thermal stress, corresponding to \~1400 kg tension force applied on the
end of the pipe support at 5 K. The hoop tension on the Invar pipe is
provided by a radially outward force of \~0.06 kg on each spider.

A test of the cryogenic reliability of Invar pipe welds was performed
\[20\] as part of the VLHC R&D program. A 50m Invar tube containing 128
automatic girth welds was thermally cycled 1000 times from 300K to 77K
with the ends constrained. No leaks were detected.

######  Longitudinal Anchoring for Magnet and Cryogenic Pipes {#longitudinal-anchoring-for-magnet-and-cryogenic-pipes .unnumbered}

######  {#section-10 .unnumbered}

###### The magnet anchor system consists of the vacuum barriers, the force-anchors, the transportation locks and the vacuum jacket anchors, as shown in Figure 5.10.  {#the-magnet-anchor-system-consists-of-the-vacuum-barriers-the-force-anchors-the-transportation-locks-and-the-vacuum-jacket-anchors-as-shown-in-figure-5.10. .unnumbered}

![](media/image11.wmf){width="5.986805555555556in"
height="2.308333333333333in"}

Figure 5.10. Longitudinal Anchor Schematic. The vacuum jacket and all
pipes are anchored every 135m.

The basic philosophy is to longitudinally anchor the vacuum jacket and
all piping at a single point near the corrector location at the
half-cell boundary (every 135m). Two 67m magnets will be hard-welded
together into a single 135m assembly. The vacuum jacket is connected to
the ground by the jacket anchors at the end of the 135m assembly. These
points define an immovable magnet cross-section in case of accidental
vacuum loss and jacket thermal contraction from a cool down to about 250
K \[14\]. There will be expansion joints in the vacuum jacket and beam
pipes on one side of this anchor. Magnet adjusters will permit 2-3cm of
longitudinal motion for normal tunnel temperature variations.

Cryogenic piping will be anchored at the 135m locations, and will have
sliding supports in places where it is not anchored. Either Invar or
Stainless Steel piping can be used for the normal cryogenic piping.
Stainless pipes will need with compensation bellows every \~33 m to
reduce shrinkage to the level of \~100 mm. The convoluted length of the
bellow is 100/0.25 = 400 mm. The force to expand the bellows by 50 mm is
300 kg for the bellows' spring constant 6 kg/mm. The bellows' stability
problem is solved by using the internal tube liner and the outer
protecting skin.

Vacuum barriers and quench pressure reliefs occur at the anchor location
in every 8^th^ magnet (540m). The vacuum breaks are used to insulate
subsystems in order to facilitate installation, troubleshooting, and
repair. It provides a good vacuum in the transmission line ring section
\[11,12\]. The vacuum barriers are designed to withstand a differential
pressure of 0.15 MPa and to minimize the heat in-leak \[13\]. They are
made of an all-welded construction of thin-wall stainless steel tubes.
The vacuum barrier is located close to the pipe longitudinal anchor to
prevent damage to the ceramic insulators that electrically isolate the
Invar conductors.

The pipe force anchor restrains thermal forces from Invar pipe shrinkage
and stainless steel bellows expansion (\~3000 kg) during cool-down and
warm-up. This anchor consists of carbon tie rods and a G-10 spider, and
connects all the pipes to the vacuum jacket.

The transportation lock is located on the opposite end of the magnet
from the vacuum break. It is mounted in place during production and
removed after magnet installation in the tunnel.

###### Cryostat Interconnection {#cryostat-interconnection .unnumbered}

After magnet alignment, interconnection activities will take place. The
magnet and the cryo-service line must be connected every \~67.75 m at
the 3.5 m and 1 m interconnection regions, as shown in Figure 5.11.

![](media/image12.wmf){width="5.986805555555556in"
height="2.584722222222222in"}

Figure 5.11. Magnet interconnections

Both conductors will be spliced at these areas. To compensate magnetic,
thermal and hydraulic forces in the region where the transmission line
conductors make a loop and are located close to each other, an
additional set of special spacers and clamps will be used. The weld on
the conductor line pipes can apparently take place directly over the
copper/superconductor structure without damaging it \[15\].

NEED WORDS (& PICTURES?) ON ACTUAL SPLICING METHODS

Three cryo-service pipes having bellows will be orbital welded
automatically. An aluminum thermo-shield made from two pieces will cover
all the pipeline connections \[16\]. Multi-layer insulation blankets are
mounted around the shield to reduce radiation heat load. The vacuum
jacket is connected by a bellows in the 3.5 m region and by a thin steel
skin in the 1 m region.

Beam pipes are connected by bellows every 135 m in the space between
corrector magnets to compensate \~25 mm motion of the magnets from
expected temperature excursions in the tunnel.

#### References *{ ed. note -- for Sec. 5.1.2.3}* {#references-ed.-note-for-sec.-5.1.2.3 .Reference-heading .unnumbered}

**\[GW FOSTER STILL NEEDS TO LOOK OVER THESE REFERENCES\]**

\[1\] V. Tsvetkov, "Transmission Line Magnet Mechanics", TD TN XXXX
2001.

\[2\] V. Tsvetkov, "Alignment of the Transmission Line Magnet in the
tunnel", TD TN XXXX 2001

\[3\] V.S.Kashikhin, "Transmission Line Magnet for VLHC. Magnetic Forces
and Magnet Deflection," TD TN XXXX. February 2001.

\[4\] V.S.Kashikhin, "Mechanical model 2 test results", TD TN XXXX.
February 2001.

\[5\] M. McAshan, "Cryogenic System for the 3 TeV Injector Study",
Fermilab TN-XXXX,1997

\[6\] I.Novitski, "Analysis of the spider support", TD TN XXXX 2001

\[7\] E.C. Quimby et al., "VJR/VJRR Design, Construction, Installation,
and Performance," ACE, vol. 43, New York, 1998.

\[8\] G. Grygiel et al., "Status of the TTF Cryogenic System," ACE
vol.41, New York, 1996

\[9\] K. Hosoyama et al., "Development of a High Performance Transfer
Line System", ACE vol. 45, 2000

\[10\] G.W.Foster, "Transmission Line Magnet R&D", Second Annual VLHC
Meeting, Danfords, Port Jefferson Long Island, NY, Oct. 16-18, 2000

\[11\] V. Parma et al., "The Insulation Vacuum Barrier for the Large
Hadron Collider Magnet Cryostats", ICEC 18

\[12\] B. Jenny et al., "A Composite vacuum Barrier for the LHC Short
Straight Section", ACE vol.41, New York 1996

\[13\] "Technical Specification for a Compound Cryogenic Helium
Distribution Line for the Large Hadron Collider (LHC)", IT-2399/lhc/lhc,
Geneva, Switzerland, December 1997.

\[14\] M. Chorowski, "Risk analysis of the LHC cryogenic system", ACE
2000

\[15\] G.W.Foster, "Status Report on the Transmission Line Magnet",
Fermilab report, September 1997

\[16\] R.C. Niemann, "Model SSC Dipole Magnet Cryostat assembly at
Fermilab", Supercollider 1, New York 1989.

\[17\] I.Novitski "Beam pipe mechanical design" TD TN XXXX 2001.

\[18\] ULTEM 2300 is a 40% glass-filled polyetherimide marketed by GE
plastics. It was developed for use in SSC quadrupole support posts by
Sondericker et. al., proc. Supercollider 4.

\[19\] "Mechanical Load Cycling Tests of the Transmission Line Spiders",
G.W.Foster, May 2001.

\[20\] R. Walker et. al., "Thermal Cycle Testing of Invar Pipe Welds"

### 5.1.3 Corrector Magnets {#corrector-magnets .unnumbered}

The Stage 1 magnets have independently powered dipole, quadrupole and
sextupole correctors in the 3.5m free space at the boundary of each 135m
halfcell. See Figure 5.2. Horizontal or vertical dipole correctors occur
at each horizontally focusing or defocusing location. The specified
strength of 0.5 T-m is sufficient to control closed orbit errors due to
misalignments, dipole strength errors, and ground settling (section
3.2.3). Dipole correctors can perform a full aperture scan at energies
up to 7 TeV and can produce a 3mm "3-bump" in the closed orbit at full
energy. Quadrupole correctors have sufficient strength to overcome the
gradient shift from magnet saturation (Figure 5.6) and can be used to
diagnose and correct β-waves in the lattice (section 3.2.3.2). Sextupole
correctors also have the strength to overcome dipols.saturation effects
at full energy (Figure 5.5) as well as regulation of chromatic effects
(section 3.2.2.3).

Higher multipole correctors have not yet been specified. In addition to
the 3.5m space at halfcell boundaries, the accelerator lattice design
includes an unallocated 1m space at the ¼ cell point) which could be
used for a Neuffer-Simpson type multipole corrector scheme.

1.  
2.  
3.  
4.  
5.  
6.  

Table 5.5. Corrector Parameters

+--------------------------------+---------+-------+--------+---------+
| Corrector type                 | Hor     | Ver   | Quadr  | Se      |
|                                | izontal | tical | u-pole | xtupole |
|                                |         |       |        |         |
|                                | Dipole  | D     |        |         |
|                                |         | ipole |        |         |
+--------------------------------+---------+-------+--------+---------+
| Quantity                       | 1720    | 1720  | 3136   | 3136    |
+--------------------------------+---------+-------+--------+---------+
| Maximum magnet strength        | 1.0 T   | 1.0 T | 25 T/m | 1750    |
|                                |         |       |        | T/m²    |
+--------------------------------+---------+-------+--------+---------+
| Field quality, 18 mm diameter  | 1.0     | 1.0   | 1.0    | 1.0     |
| area, %                        |         |       |        |         |
+--------------------------------+---------+-------+--------+---------+
| Effective magnet field length, | 0.5     | 0.5   | 0.5    | 0.8     |
| m                              |         |       |        |         |
+--------------------------------+---------+-------+--------+---------+
| Integrated field at r = 1 cm,  | 0.5     | 0.5   | 0.125  | 0.14    |
| T\*m                           |         |       |        |         |
+--------------------------------+---------+-------+--------+---------+
| Magnet core length, m          | 0.48    | 0.48  | 0.5    | 0.8     |
+--------------------------------+---------+-------+--------+---------+
| Current, A                     | 25      | 25    | 1.0    | 1.0     |
+--------------------------------+---------+-------+--------+---------+
| Voltage, V                     | 23      | 23    | 140    | 175     |
+--------------------------------+---------+-------+--------+---------+
| Power, W                       | 600     | 600   | 150    | 200     |
+--------------------------------+---------+-------+--------+---------+
| Number of coils per magnet     | 1       | 1     | 4      | 6       |
+--------------------------------+---------+-------+--------+---------+
| Number of turns per coil       | 640     | 640   | 1240   | 633     |
+--------------------------------+---------+-------+--------+---------+
| Copper conductor diameter, mm  | 5 x 5   | 5 x 5 | 1      | 1       |
+--------------------------------+---------+-------+--------+---------+
| Copper weight, kg              | 250     | 250   | 40     | 50      |
+--------------------------------+---------+-------+--------+---------+
| Core weight, kg                | 300     | 220   | 30     | 50      |
+--------------------------------+---------+-------+--------+---------+

The main design issue for the correction system is the fringing field
generated by the 100 kA conductors in the drift space between dipole
magnets. This field is 0.3 T in an unshielded beam pipe and causes
magnetic forces of 700kg/m on the superconducting cable. The distance
between the outer shell of the superconducting transmission line and the
vacuum chamber center is only 30 mm; it is a nontrivial task to form the
needed correction field in this area. Several options were considered to
solve this problem:

7.  Compact superconducting correctors with cold ferromagnetic screen
    \[*need ref:* TD Note N. Andreev\]

8.  Room temperature correctors with iron core as a ferromagnetic screen

9.  Room temperature correctors with the transmission line deflected
    downwards and out of the way in the corrector region;

10. Pole tip windings on the main dipoles (effective at injection, less
    useful at high fields)

11. Iron-dominated mechanical correctors ( low power, stepping motor
    drive)

12. Permanent magnet correctors (rotational multipoles, stepping motor
    drive)

Option 3 (warm correctors with out-of-the-way transmission line) was
chosen for this Design Study on the basis of lowest overall design risk
and predictable costs. Other options may be used only if further R&D
indicates that their total cost will be less than Option 3.

The six correctors in the 3.5m space at each halfcell will be
pre-aligned and transported on a common skid. See section 5.1.8.6. All
the correctors can be installed and removed without breaking the beam
pipe vacuum.

Figure 5.12. Horizontal dipole correctors

Figure 5.13. Quadrupole correctors.

![](media/image13.wmf){width="3.658333333333333in" height="2.4875in"}

Figure 5.14. Sextupole correctors.

The powering scheme for the correctors is discussed in section 5.2.3.
All correctors are independently powered so that if necessary they can
be programmed to overcome both random and systematic errors in the
saturation characteristics of the magnets.

There is significant scope for reduction of corrector strengths. One
rather promising approach is to optimize pole profiles for low field and
saturation correction hole positions for maximum field. In this case,
correctors will work at full power for only a short period of time
during the acceleration cycle and will return to near zero at full
field. This will reduce the operational cost of the corrector power
supplies and simplify cooling.

### 5.1.4 Interaction Regions {#interaction-regions .unnumbered}

The VLHC has provisions for two large colliding experiments located on
the present Fermilab site. A system of magnets on each side of the
interaction regions is required to bring the beams into collision. With
these magnets come additional requirements for the accelerator including
power supplies, beam absorbers to protect the magnets and prevent
activation of the tunnel, and an alignment system for the magnetic
elements. For the superconducting magnets there is quench protection
system, cryogenics, and interconnects for room temperature to cold
transitions of instrumentation and powering.

Figure 5.15 shows a schematic of the interaction regions magnetic
elements. Each interaction region spans a space of 6 half cells, from 20
meter to approximately 810 meters from the interaction points. The
interaction regions consists o eighr high gradient "inner triplet"
quadrupoles, fouo beam separation/recombination dipole elements, and an
outer system of lower gradient quadrupoles. There will also be orbit and
local field corrector magnets. The separation dipoles, "outer"
quadrupoles and correctors are identical to those used elsewhere section
5.1.5).

![](media/image14.wmf){width="4.897222222222222in"
height="2.5444444444444443in"}

Figure 5.15. Principal magnetic elements for the VLHC-1 interaction
region.

#### 5.1.4.1 Low-beta IR quadrupoles {#low-beta-ir-quadrupoles .unnumbered}

These magnets form the final focus at the two collision points. The
required gradient is 300 T/m with a length of 10 meters and a single
aperture of \~80 mm. The field quality must be very good because the
beams could be separated by as much as 12.5 mm due to the crossing
angle.

A design developed by INFN-LASA for a possible upgrade of the LHC low-β
quadrupoles, with an aperture of 85 mm \[1\], can be used as a starting
point to meet these requirements. The basic design as shown in Figure
5.16 has two Nb~3~Sn layers in a cos (2Θ) geometry, wound using the
cable described in Table 5.6. The cable has a target critical current
density of 3000 A/mm^2^ @ 4.2 K, 12 T \[2\]. Internal splices can be
avoided using the double pancake technique. The main characteristics of
the magnetic design are reported in Table 5.7. The field quality of the
basic design (aperture = 85 mm) gives acceptably low values for the
allowed harmonics. The value of the b6, b10 and b14 multipoles,
normalized to the gradient and using a 10 mm reference radius are
respectively 1.5 e-6, 1.6 e-8 and \< 1.0 e-9. The relative field error
is lower than 1.1 e-5, at 12.5 mm from the center on the midplane. Iron
saturation effecas remain to be studied.

Table 5.6: Conductor Characteristics for Low-Beta Quadrupole

  ------------------------------------------ ----------------------------
  Superconductor                             Nb~3~Sn

  Critical current non Cu (@ 4.2K 12T)       3000 A/mm^2^

  Strand diameter                            0.825 mm

  α = Cu/nonCu                               1.3

  Number of strands                          36

  Cable dimension                            1.34 ÷ 1.60 x 15.0 mm^2^

  Effective filament diameter                \< 40 μm
  ------------------------------------------ ----------------------------

![](media/image15.wmf){width="3.298611111111111in"
height="2.040277777777778in"}

Figure 5.16. Basic design cross section with field quality at maximum
gradient

> Table 5.7: Magnetic design characteristics at short sample limit

  -------------------------------------- --------------------------------
  Aperture                               85 mm

  Gradient                               300 T/m

  Current                                20218 A

  Self inductance                        4 mH/m

  Stored energy                          820 KJ/m

  Horizontal Magnetic force (per octant) 2.78 MN/m

  Vertical Magnetic force (per octant)   3.43 MN/m

  Number of turns                        10 + 4 + 19

  Collars thickness                      20 mm

  Iron inner radius                      93.5 mm
  -------------------------------------- --------------------------------

The quench protection has been studied at an operating current
corresponding to 93% of the short sample limit. Simulations were
performed using a version of the QLASA code \[3\] modified at Fermilab
\[4\] for the study of FNAL Nb~3~Sn high field magnets. These studies
show that full coil coverage by heaters on both layers is required, and
the delay time between the spontaneous quench start and the beginning of
the heater-induced quench must be very short. This solution has an
impact on magnet technology, because if the insulation of the heaters
between the inner and outer layers cannot withstand the conductor heat
treatment, the double pancake technique must be abandoned. Furthermore,
protection redundancy will not be possible (or at least very
complicated) and fault scenarios have to be addressed. The short time
delay necessary to avoid excessive hot spot temperature and the lack of
protection redundancy should be the object of an appropriate R&D.

A possible solution for the mechanical design is the one proposed for
the upgraded version of the LHC IR low-beta quadrupoles presented in
\[5\]. It uses 20 mm thick stainless steel collars, which can provide
part of the required prestress and magnetic force containment. The rest
of prestress and support are provided by a thick skin. The yoke is only
in contact with the collars close to the midplanes, in order to transfer
the stress from the skin to the coils where it is most necessary. The
effectiveness of this design for the higher forces developed in the VLHC
IR quadrupoles is still under investigation. A finite element analysis
of coils and collars, simulating the rest of the mechanical structure by
use of an external load, showed that the maximum stress in the coil can
be kept below 160 MPa. The design of yoke, skin and contact regions must
still be optimized to provide the required support on the coils.

In summary, it can be concluded that a two layer design using Nb~3~Sn at
4.2 K is a good candidate to meet the requirements for these magnets, if
the critical current target is reached. Some design optimization will be
required for the quench protection and mechanical design.

#### 5.1.4.2 Interaction Region Subsystems {#interaction-region-subsystems .unnumbered}

Most of the 1600 meters of the interaction straight section will be in
the standard VLHC tunnel. Since these magnets elements need to be
"tunable" they require a special gallery to handle the power supply and
electronics of these magnets. There will likely be a global alignment
system that connects the experiments to the final focussing elements.
Finally, the tunnel will need to be wider near the IP to accommodate the
extra shielding and vacuum connections and instrumentation associated
with the collision detection and IP interconnect.

Four independent power systems are required for each side of an
interaction region: one for the inner triplet, one for each separation
dipole and one for the outer quadrupoles. Additional quadruples in the
IR region will likely be powered in series with other straight section
quadrupoles in the accelerator and are not include here. The high
gradient quadruples require a 25 kA, 10 Volt supply, the conventional
separation dipoles require 1 kA, 100 Volt supplies while the
conventional outer quadrupoles need a 7kA, 10 volt supply.
Superconducting correctors will be powered independently with supplies
comparable to the outer quadrupole conventional correctors except that
quench and lead protection systems will be required.

Superconducting circuits will rely on quench heaters for protection.
With the relatively small amount of stored energy (50 MJ) and small
number of magnets/circuit (4 or less) it is not clear whether the
complications of an extraction circuit and bypass diodes are worth the
effort. Thus, in the event of a detected spontaneous quench, the circuit
power converter will be phased off, all quench protection heaters on all
the magnets in a circuit will be energized.

As stated, inner triplet quadruples will likely need protection levels
comparable to or greater than a similarly sized LHC IR quadrupole
magnet. Thus 4-8 quench heater circuits plus the requisite electronics
are required for each magnet. The total space for power supplies and
electronics required for each quench heater circuit is approximately 2
6U VME crates. Thus a space of approximately 70 6U crates are required
for each side/IR.

LCW and electrical power will be required for the power supplies and
conventional magnets. The LCW system will be required to deliver several
hundred liters/minute per IR.

Superconducting magnets rely on 4.5 K helium. The estimated dynamic heat
load/side/IP will be approximately 600 Watts or 2.4 kW for both
interaction regions \[6\]. Local heating in the quadrupoles could be
quite large due to the strong focusing elements (G.dl \~ 3000 T/m \*m).
This could be a non-negligible load on the Phase I cryogenic
requirements.

This heat load, if taken directly by the 4.5 K helium will require
approximately ½ of a VLHC-1 power plant. Thus the cryogenic plant
located on site would have to be upsized. Since the IR temperature and
pressures profiles and requirements will differ from the transmission
lines, there will likely be a need to be a separate transfer line from
the cryogenic system. The helium requirements might be reduced by
carrying away some of the heat load by actively cooled absorbers in the
80 mm beam tubes.

A distribution box will be required in order to make a connection
between the room temperature and cryogenic electrical elements, as well
as supply the cryogens to the magnetic elements. Elements include
voltage taps, strip heater leads, thermometry and other cryogenic
instrumentation. 25-30 kA HTS leads would be used to supply the
excitation currents.

A particle absorber system will be required to protect the IR magnets
from the excessive radiation from particles produced from the
interaction region. Using the LHC as a guide, the system will require a
hadron and neutral particle absorber. The primary hadron absorber will
be located on the IP side of the inner triplets. The size of the
absorber will be comparable to the LHC absorber but will have
significantly larger heat loads, estimated to be 2 kW per IR \[7\]. Thus
an actively cooled absorber will likely be necessary. The neutral
absorber, located between the separation dipoles would be necessary to
protect the outer quadrupoles, possibly the transmission line magnets
and the walls of the tunnel from activation. It, too, will likely need
to be actively cooled. If water cooled the requirements would be modest
and would be parasitic to the magnet and power supply LCW system.

Alignment tolerances are likely to be comparable to those of the LHC
Interaction region. Transverse alignment tolerances will thus need to be
on the order of 100-300 microns over both sides of the IP. Thus an
alignment system will be required to tie together the two sides of the
IR and the detector.

#### References *{note -- for sec. 5.1.4}* {#references-note-for-sec.-5.1.4 .Reference-heading .unnumbered}

\[1\] G. Ambrosio et al. *"Preliminary Proposal of a Nb3Sn Quadruple
Model for the Low-beta Insertions of the LHC"* INFN Report,
INFN/TC-95/25, Sept. 13, 1995.

\[2\] R. Scanlan, *"Conductor Development Program"* Low Temperature
Superconducting Workshop, Santa Rosa (CA), Nov. 8-10, 2000.

\[3\] M. Canali, L. Rossi, *"DYNQUE: a computer code for quench
simulation in adiabatic multicoil superconducting solenoids"*, INFN
Report, INFN/TC-93/06, 1993

\[4\] L. Imbasciati, G. Ambrosio, P. Bauer, V. Kashikhin, A. Zlobin,
*"Quench Protection of the Common Coil Racetrack (CCRT-1)-Results of
Adiabatic Model Calculations",* TD-00-056, FNAL (Sept. 2000)

\[5\] G. Ambrosio, G. Bellomo and L. Rossi, *"A 300 T/m Nb3Sn Quadrupole
for the Low-beta Insertions of the LHC"*, Proc. of EPAC96, Sitges
(Barcelona), p. 2290.

\[6\] Nikolai Mokhov, private communication

\[7\] Bill Turner, private communication

### 5.1.5 Special Collider Ring Magnets {#special-collider-ring-magnets .unnumbered}

This section describes several different magnets installed in the
straight sections of the ring. There are a total of 10 straight
sections, 5 in each half of the ring. On the Fermilab site there are two
Interaction Region straight sections, two Utility straight sections and
one Beam Crossing straight section. The straight sections on the
opposite side of the collider are basically the mirror reflection of
what is on the Fermilab site, except that there are no IRs or utility
equipment installed in this area.

Beam focusing in the standard straight sections is provided using a
classical FODO cell made of four quadrupoles. The cell half-length is
135 m. The basic lattice is modified for special insertions as described
in section 3.2.1.

Both superconducting \[1\] and conventional quadrupoles were considered
for the straight sections. Conventional water-cooled copper magnets are
preferred because of their lower cost and ease of system integration. No
warm-to-cold transitions, gate valves, etc. are required between the
quadrupoles and the \~100m of warm beam pipe between quads. The compact
quadrupoles in both rings can be installed side-by-side at the basic
beam-beam spacing of 150 mm or at non-standard beam spacings as required
by special insertions. It easy for extracted beamlines to miss the warm
quads due to their low profile and absence of a cryostat. Warm magnets
are more tolerant than superconducting magnets of the beam losses that
occur in beam transfer and beam cleaning insertions. The cooling water
system needed for warm quadrupoles is absent in the arcs but is already
present in the straight sections to service other systems.

#### 5.1.5.1 Straight Section Quadrupole {#straight-section-quadrupole .unnumbered}

This quadrupole uses water-cooled windings and has been designed so that
a pair of them can be installed side-by-side in both rings. The 150mm
beam spacing and the required beam pipe size of 20 mm implies certain
restrictions on the achievable quadrupole field gradient. The chosen
reference gradient of 69.3 T/m results in the basic quadrupole length of
6.1 m. The preliminary magnetic design indicates that field quality is
not going to be a problem since there is plenty of space to make the
needed pole shaping. The magnetic field in the steel is acceptable,
reaching 1.9 T at the pole base, but there are regions where the field
exceeds 2.0 T at 70 T/m so good quality low carbon steel must be used.
Table 5.8 summarizes the quadrupole features. A cross-section of the
quadrupole is shown in Figure 5.17.

![](media/image16.wmf){width="3.5506944444444444in"
height="2.3444444444444446in"}

Figure 5.17. The straight section quadrupole is a conventional
water-cooled copper design that allows two magnets to be mounted side-by
side with the standard beam separation of 150mm.

Table 5.8. Parameter list for the conventional straight section
quadrupoles

  --------------------------------------------------------- -------------
  Number Required **CHECK THIS**                            464

  Gradient, T/m                                             70

  Pole diameter mm                                          22

  Length, m (typical)                                       6.1

  Width, mm                                                 148

  Height, mm                                                168

  Number of coils per winding                               4

  Number of turns per coil                                  12

  Conductor cross section area, mm^2^                       61.5

  Resistance of the winding, Ohm                            0.18

  Rated current, A                                          285

  Voltage drop, V                                           53

  Power consumption, kW                                     15

  Conductor hole diameter, mm                               5

  Water temperature rise at 1 MPa (deg. C)                  12

  Water flow per quadrupole (l/min)                         17
  --------------------------------------------------------- -------------

5.1.5.2 Beam Cross-Over Section

The two beam cross-over regions in the collider are introduced to make
the perimeters of the counter-rotating rings equal. To accommodate the
magnets in the cross-over region, a short straight section is used that
consists of a focusing cell that differs from the standard focusing
cell. At the entrance to the cross-over region, the two beams are in the
horizontal plane, separated by 150 mm. To make a cross-over, it is
necessary to bring the beams together horizontally, separate them
vertically before the crossing, and make the opposite transformation
after the crossing. The vertical shift of each beam required to
eliminate beam-beam interaction effects is 4.5 mm, which results in a
beam-beam separation of 9 mm, more that 18 σ. To reduce the number of
magnets required for beam manipulation, tilted dipoles are used to bend
beams both horizontally and vertically. The cell layout is shown
schematically in Figure 5.18.

The magnet length L~m~ and tilt angle θ can be found based on nominal
magnetic field and length of gaps between the magnets in the string. As
in the arc dipoles, the transmission line is used for magnet excitation.
Moreover, because of the large required pole width of the magnet, the
return line is also used as an active part of the magnet excitation
winding. To minimize iron core saturation effects, a magnetic field of
B~m~=1.95 T was chosen, as it was for the arc dipoles. With two-meter
gaps introduced between the magnets to allow some space for
repositioning of the transmission line, this results in a magnet length
of 34.95 m and a tilt angle of θ = ± 6.84°.

![](media/image17.wmf){width="4.102083333333334in"
height="2.2680555555555557in"}

Figure 5.18. Cross-over straight section layout

The total length of the beam cross-over magnetic system is about 150 m.
The magnet cross-section is shown in Figure 5.19. The dipole gap is 44
mm to accommodate (while tilted) the two beams with their vacuum pipes.
The pole width provides a good field region for beams separated by 150
mm. Because of the big difference in gap thickness for the pole and flux
return regions, the force applied to the cable is significant, up to
2000 kg/m for this magnet. Special measures must be taken to strengthen
the cable \"spider\" to the needed level at this location.

![](media/image18.wmf){width="4.225in" height="2.7069444444444444in"}

Figure 5.19. Beam crossing dipole

To allow a 150-m gap for the tilted magnet installation, the basic
focusing cell was modified, resulting in an increased length of the cell
quadrupoles: 18.96 m for each of the two inner quadrupoles and 16.94 m
for each of the two outer quadrupoles. Significantly increasing the
basic quadrupole length above 6 m would result in an increased cooling
water temperature rise, so the total required focusing strength can be
obtained mostly by increasing the number of quadrupoles. The total
length of quadrupoles installed in the two rings for each of the two
cross-over sections is 143.6 m.

#### 5.1.5.3 Conventional Magnets for the Interaction Region {#conventional-magnets-for-the-interaction-region .unnumbered}

As described in section 5.1.4, the IR straight section requires some
beam manipulation to allow using the low-beta high gradient quadrupoles.
For this purpose, so called \"separation/recombination\" dipoles are
used that bring the two beams together within the low-beta lens string
region and place the beams onto the nominal orbits before they go into
the regular part of the straight section (see Figure 5.15).

The existing transmission line cable is used for excitation of these
magnets and 1.95 T maximal magnetic field in the dipoles has been
chosen. As it follows from section 2.1.1, the gap available for
installation of the bending magnets is about 125 meters. Leaving some
space for the transfer line position manipulation, a magnet length of 28
m was chosen to insure that a 75-mm beam shift within the 120-m gap in
the lattice. Beam displacement inside this dipole is about 12 mm. This
displacement must be taken into account when the good field region of
the dipoles is being specified.

To bring the beams together, the \"recombination\" dipole simultaneously
bends the two beams separated by 150 mm. This requires one direction of
bending field for both beams. The \"Separation\" dipole separates beams
moving in the opposite directions. Final beam separation at the outer
edge of the magnet is 24 mm. To reduce the force applied to the
transmission line and to avoid field asymmetry, a symmetrical iron core
configuration was chosen. The magnet cross-section is shown in Figure
5.20. The good field region area for this dipole is 35 x 20 mm, which is
enough to accommodate the two shifted beams.

![](media/image19.wmf){width="3.098611111111111in"
height="2.204861111111111in"}

Figure 5.20. Separation/Recombination Dipole used for the Utility
Straight Sections and IRs.

The double-channel separation dipole makes use of both the arc dipole
excitation line and the return transmission line. As it was for the
single aperture dipole, the gap height is 26 mm. Maximal force applied
to the superconducting cable is about 65 kg/m at maximal field strength.
The magnet cross-section is similar to shown in Figure 5.19 above,
except the pole gap and pole width are smaller resulting in a more
compact magnet with 650 x 350 mm^2^ cross-section. The good field area
of the dipole is 185 x 20 mm^2^, which is slightly larger than necessary
for this dipole location. This allows using the dipole in the utility
straight section where larger beam separation is required.

Besides the separation/recombination dipoles, each of the two IR
sections requires a set of focusing quadrupoles similar to that
described in section 5.1.5.1. The required strength of these quadrupoles
can be found in Table 5.7. The total length of 70 T/m quadrupoles for
use in each of the two FNAL-site IR sections is 445.1 m. Quadrupoles
with lengths longer than 6.1 m will be composed using two quadrupoles.

#### 5.1.5.4 Utility Section Conventional Magnets {#utility-section-conventional-magnets .unnumbered}

The utility straight section is introduced into the ring lattice to
provide the space needed for various accelerator systems, such as the RF
cavities, and the injection, extraction, and abort systems. In the RF
utility sections the required beam separation is 460 mm. To manipulate
the beams, separation dipoles are used similar to those used in the IR
sections. At the input and the output to the section, these dipoles have
an air gap width that accommodates both beams. In the middle of the
section, individual separation dipoles are installed back-to-back in
both rings. The cross-section of the dipole can be found above (Figure
5.20). The length of the dipoles in the utility section is 25 m, which
allows shifting of each beam by 155 mm within the 242-m space as is
shown in Figure 5.22 below.

Two types of quadrupoles are used in the Utility section. Most of the
quadrupoles are identical to the 70 T/m straight section quadrupoles
described earlier. The total length of this type of quadrupole used in
each of the two FNAL-site utility sections is 208m. The quadrupole
triplet installed between the abort system kicker and Lambertson
requires more radial space to accommodate the beam deflected by the
kicker. In each of the two FNAL-site utility sections, 58.9 meters of
these quadrupoles, described below, are to be fabricated.

Because it provides the needed interface with Tevatron, used as an
injector, and with the beam dump facility, it is relevant at this point
to review the injection/extraction scheme of the machine. As described
in Chapter 4, the Tevatron, run bipolar, is used to inject protons into
the collider rings. Beams for both collider rings are extracted using
two sets of equipment installed at B0 area. Two identical injection
transfer lines end at the corresponding collider downstream utility
section where injection lambertsons and kickers are installed (see
Figure 5.21. ).

![](media/image20.wmf){width="3.8506944444444446in"
height="1.7013888888888888in"}

Figure 5.21. Injection and beam abort system scheme

At the end of the transfer channel, Lambertson and dipole magnets bring
proton beam into position close to an appropriate ring where it moves
almost parallel to the equilibrium orbit crossing it in the horizontal
plane. At the location of the crossing, a kicker magnet adjusts injected
beam propagation direction, so that it follows as close to the
equilibrium orbit as reasonably possible. All these magnets belong to
the injection system described below. The layout of the utility section
that includes injection line elements is shown in Figure 5.22.

![](media/image21.wmf){width="3.926388888888889in"
height="2.439583333333333in"}

Figure 5.22. Utility straight section including injection, abort, and RF
cavities.

##### 5.1.5.4.1 Injection System {#injection-system .unnumbered}

The injection optics fit comfortably into the long 350m drift in the
utility region. The injection uses a full-aperture kick which does not
restrict the circulating aperture. The layout, working backwards from
the injection point, is as follows: Six meters of pulsed kicker magnets
with magnetic field 0.05 T provide the horizontal angular kick of 0.1
mrad to the injected beam. The horizontal separation between the
injected and circulating beams is 25 mm at the nearest Lambertson 250
meters away. A total of 6 m of Lambertsons operating at 0.8 T provide a
vertical angular kick of 1.6 mrad. The Lambertsons are short enough that
no separate asymmetric design is needed. The clearance at the nearest
quad (100m away) is 160mm, large enough to allow unobstructed placement
of standard quadrupoles on both the injected and circulating beamlines.
The vertical clearance at the RF station (300m from the Lambertsons) is
480mm. If desired this separation can be increased using normal dipoles
to begin part of the 30 mrad up-bend needed for the slope of the
transfer line ramp.

The injection kicker parameters are listed in Table 5.9. The duration of
the kick provided to the injected beam is \~20 μsec and is defined by
the length of the extracted beam pulse from the Tevatron. The magnetic
field rise time is about 150 nsec; this defines the minimum time
separation between successive injected batches. To allow a reasonable
amount of time for the abort kicker current rise, a three-microsecond
gap is arranged between the first and the last injected batches. This
gap also sets the requirement for the current decay time in the
injection kicker. Because the kicker magnet must be rather fast, working
in the MHz frequency range, it is difficult to use a high magnetic field
in this device. As a reasonable reference field value, 0.05 T field
strength is used for this study, close to that used for SSC injection
system with similar pulse shape requirements \[2\]. The system is
composed of 6 separate modules, each 1 m long. Each module is fed by an
individual pulse forming network (PFN). A C-shaped magnet is made from
ferrite blocks and with additional capacitors forms a twelve-cell lumped
delay line with a characteristic impedance of 16.6 Ohm. The ceramic beam
pipe has thin resistive coating on the inside surface, and conductive
strips for image current on the outside.s. Equivalent PFN/kicker circuit
does not differ much from the SSC \[2\].

Table 5.9. Injection Kicker System Parameters

  ---------------------------------------------- ------------------------
  Number of modules                              6

  Length of Module (m)                           1

  Maximum field (T)                              0.05

  Rise time (0 to 100%) (nsec)                   150

  Fall time (μsec)                               3

  Impedance (Ohm)                                16.6

  Maximum current (kA)                           2.1

  Maximum voltage (kV)                           70
  ---------------------------------------------- ------------------------

The injection Lambertson provides the needed bending strength to steer
the injected beam out of the vicinity of the circulating beam. The
cross-section of an asymmetric design is shown in Figure 5.23. It
appears that a symmetric design alone may be sufficient. The magnet pole
with the field free region is made of a solid piece of annealed, low
carbon steel to reduce magnetic field in the field free region. To
simplify vacuum problems, the pole is enclosed in a thin-wall stainless
steel shell. The pole gap is fixed with the use of stainless steel
spacers. For magnet excitation, conventional copper wire coils are used.
Water cooling can be omitted due to the low duty cycle (5 seconds flat
top with 1 minute cycle time) dssumed for this study. The main
parameters of the Lambertson are summarized in Table 5.10 below.

![](media/image22.wmf){width="3.83125in" height="3.238888888888889in"}

Figure 5.23. Injection Lambertson magnet (asymmetric version).

Table 5.10. Parameter list for the Injection Lambertson magnet

  --------------------------------------------------------- -------------
  Magnetic field, T                                         0.8

  Pole spacing, mm                                          25

  Length, m                                                 4

  Width, mm                                                 288

  Height, mm                                                260

  Number of coils per winding                               2

  Number of turns per coil                                  42

  Conductor cross section area, mm^2^                       42

  Resistance of the winding, Ohm                            0.32

  Rated current, A                                          208

  Voltage drop, V                                           70

  Maximal power consumption, kW                             15

  Average power consumption, kW                             1.25

  Magnet surface temperature rise, °C                       20
  --------------------------------------------------------- -------------

Transfer line dipole magnets, that do not have field free region, have
been designed using the same coil cross-section. Because pole width can
be made significantly smaller, and because no vacuum shell is required
for this magnet, it is even more compact, 180 x 180 mm^2^ in
cross-section, with pole gap of 25 mm and magnetic field reaching 0.8 T.
The rest of the magnet parameters are very close to those shown in Table
5.10.

Besides vertically bending magnets, horizontal bending with total angle
of 80 mrad (not completely justified at the moment) is required in the
transfer channel. This bend can also be made using the magnets of the
same type. Total magnet string length required for this bend in both
transfer lines is about 300 m.

For this study, conventional magnets have been chosen to establish a
reference point for a future research work with the goal of building the
transfer channel using only permanent magnet based equipment. Although
this technique is well studied during fabrication of the Fermilab
Recycler Ring, requirement of having adjusted bending and focusing
strength makes it difficult to use the system cost scaling without
making first a thorough design study of this approach. An encouraging
approach to this study has been undertaken in \[3\].

There are 86 quadrupoles installed in the transfer channels, most of
them having integrated gradient of 40 T. With quadrupole gradient of 40
T/m, length of the quadrupoles is 1 m. Using design similar to described
in chapter 5.1.5.1, and intermittent powering with only about 0.8 kW of
maximal power per a lens, we can employ air cooling that results in
about 10 °C temperature rise at the surface of the magnet.

##### 5.1.5.4.2 Beam Abort Magnets  {#beam-abort-magnets .unnumbered}

The abort magnet system consists of a kicker magnet, Lambertson, a beam
sweeper magnet and defocusing quadrupoles. System issues and Beam
Absorber design are discussed in section 5.3.2. The circulating beam
goes through the field free area of the Lambertson magnet. The beam is
kicked radially outward into the bend channel of the Lambertson magnet
which deflects it vertically upward into the beam dump channel. The
abort channel is equipped with a beam sweeper magnet to spread the
energy on the graphite absorber.

As the mangets ramp, the magnetic field of the abort kicker, Lambertson
and sweep-magnet must track the beam energy. This is accomplished
automatically for the Lambertson by energizing it with the transmission
line. The abort kicker and sweeper systems must rely on active systems
to monitor the capacitor charging voltage and force an abort if it
starts to go out of tolerance.

uadrupole

  --------------------------------------------------- -------------------
                                                      

                                                      

                                                      

                                                      

                                                      

                                                      

                                                      

                                                      

                                                      

                                                      

                                                      

                                                      

                                                      

                                                      

                                                      

                                                      
  --------------------------------------------------- -------------------

**Abort Kicker Magnets** switch the beam between the ring orbit and the
abort channel. Its strength is chosen to provide needed beam separation
of 17 mm at the entrance to the abort Lambertson located 300 m
downstream. Assuming a kicker field strength of 0.2 T, the required
length of kicker is 30 m. The cross-section of the kicker is shown in
Figure 5.24.

![](media/image23.wmf){width="3.7125in" height="2.0208333333333335in"}

Figure 5.24. Abort System Kicker Magnet

Current rise time of the extraction kicker is about 3 μsec, so a beam
abort gap of about 3 μsec is needed. This requirement results in using a
high frequency magnetic material for magnet core fabrication. Mn-Zn
MN8CX (Ceramic Magnetics) ferrite was chosen for this study. The core is
made of ferrite blocks and assembled using epoxy bonding after windings
and ceramic vacuum pipe are installed inside. At nominal field of 0.2 T,
windings current is 2410 A. Maximal field in the core is about 0.45 T,
which is below the material saturation level. Pole width was optimized
using pole profiling by attaching 1-mm ferrite stripes near the pole
wedges. With this shaping, field uniformity in the entire vacuum pipe
region is within 0.1 %, which is good enough for this device. In the
configuration shown, magnet inductance is 2.5 μH/m. Ten 3-m sections are
used, installed one following another, with each section having 7.5 μH
inductance and 2.5 ohm impedance. Each section is fed independently by
its own pulser.

The abort kicker pulser uses a two-stage scheme. The first stage
delivers high voltage for a fast current rise time. Capacitor discharge
is used at this stage. Then, in the second stage, a long SCR-generated
pulse with much lower voltage is used to support needed flat top level.
For the three-meter section, discharge capacitor with C = 0.5 μF insures
needed current rise rate. This results in the maximal voltage at the
first stage of 9600 V. Energy stored in the capacitor bank or in the
magnetic field is about 25 J. Flat top length for the abort kicker
magnet is defined by the ring circumference and is about 800 μsec. To
have this long pulse shape, a separate power source must be switched on
when current in the primary circuit starts to decay. Because this is a
typical long-pulse pulser implementation (see, for example, \[2\]), we
will not go into further details.

**Large Aperture Quadrupoles** are required between the Abort Kicker and
the Lambertson to allow for the 17mm radial displacement at the
Lambertson shown in Figure 5.22. For this quadrupole, lower field
gradient (of about 45 T/m) can be achieved, and longer quadrupole
lengths are required for beam focusing. A longer quadrupole results in
higher power consumption and cooling water temperature rise. Using two
5-meter quadrupoles instead of one 10-meter, it is possible to have a
lower water temperature rise at the expense of higher total water flux.
summarizes the major abort quadrupole parameters.

Table 5.11. Large Aperture Quadrupole Parameters

  --------------------------------------------------- -------------------
  Number Required (total both rings)                  8

  Aperture radius, mm                                 20

  Gradient, T/m                                       45

  Length, m                                           5

  Quadrupole width, mm                                260

  Quadrupole height, mm                               260

  Number of coils per winding                         4

  Number of turns per coil                            12

  Conductor size, mm                                  11.7x11.7

  Conductor cross section area, mm^2^                 104

  Coil Resistance, Ohms                               0.091

  Rated current, A                                    625

  Voltage drop, V                                     61

  Power consumption, kW                               38

  Water Hole diameter, mm                             6.35

  Water pressure drop, MPa                            1

  Cooling circuits per winding                        8

  Water temperature rise (deg. C)                     16

  Water flow per magnet (l/min)                       35
  --------------------------------------------------- -------------------

**Abort** **Lambertson Magnets** use the superconducting transmission
line as an excitation winding. This ensures that at each moment the
magnetic field is proportional to the beam energy. The magnet
cross-section is shown in Figure 5.25. The magnet part that includes
field free beam channels is placed inside a stainless steel vacuum box.
Only one field free channel is used in this device; another channel has
been added to obtain needed symmetry. The tolerable Magnetic field in
the field free area limits the maximum field in Lambertson magnet. The
deflecting gap field value of 0.8 T was chosen to have field in the
field free region on the level of 20 Gauss. The 67 m total length of the
Lambertson gives the beam a kick of 0.8 mrad that results intmore than
200 mm of beam separation at thesdownstream quadrupole and horizontal
dipole. Fagnetic forces on the transmission line conductor are about 25
kg/m. Thi. force can be handled by the standard transmission line
support spider.

![](media/image24.wmf){width="4.3in" height="3.0097222222222224in"}

Figure 5.25. Lambertson magnet

Table 5.12. Main Parameters of abort system Lambertson Magnet

  ------------------------------------------- ---------------------------
  Maximum field, T                            0.8

  Total length, m                             67

  Air gap, mm                                 20

  Field homogeneity, %                        0.1

  Maximum field in the hole, Gauss            20

  Maximum current, kA                         100

  Weight, kg/m                                330
  ------------------------------------------- ---------------------------

**Abort** **Sweeping** **Magnets** are introduced to reduce heating of
the graphite absorber block by distributing the beam energy across a
larger dump surface area. See Section 5.3.2. Although reliability of
this sweeping system must be high, the field quality requirements for
sweeping magnets can be quite modest, allowing about 10% of field
uniformity in the sweeping magnets. Sweeping magnets deflect beam in X
and Y direction with amplitude that corresponds to beam striking the
dump block at a location close to its radial dimension. If phase
difference between X and Y oscillations is 90°, beam projection on the
dump surface will move along a circular path. The velocity of this
movement must be high enough to allow beam circling around the block at
least twice during the extraction time, \~800 μsec. This requires a beam
oscillation frequency of \~2 kHz. The integrated strength of the
sweeping magnets must be about 12 T⋅m in each coordinate. A field
strength of 0.3 T was chosen for this device, resulting in 40 m magnet.
The required aperure is about 50 mm after taking into account possible
steering mistakes due to kicker malfunction and unpredictable beam
position in cases of emergency extraction. To make the system simple and
reliable, the two steering magnets are combined in a single unit, as
shown in Figure 5.26. Field uniformity in this magnet is at an
acceptable level of about 5% at reference radius of 15 mm. Positive
sextupole component in the whole aperture results in additional beam
defocusing on the target. Magnet yoke is made of standard toroidal iron
powder cores (e.g. T520-40D by Micrometals). Core effective permeability
is 60 to 150 in the frequency range up to 100 kHz and in the flux
density ranges up to 1 T.

![](media/image25.wmf){width="3.9722222222222223in" height="2.8875in"}

Figure 5.26. Sweeping magnet cross-section.

Main parameters of the magnet are summarized in Table 5.13.

Table 5.13. Sweeping Magnet Parameters

  ------------------------------------------ ------------- ---------------
  *Parameter*                                *Unit*        *Value*

  Magnetic field                             T             0.3

  Magnet length (total)                      m             40

  Maximum field in the core                  T             0.45

  Stored energy / meter                      J/m           160

  Number of turns                                          2 x 8

  Wire diameter                              mm            5

  Maximum current                            A             2000

  Inductance                                 μH            2 x 80
  ------------------------------------------ ------------- ---------------

For equipment safety reasons the sweeping magnet is made of 10 separate
4-m sections powered by independent pulsers. Simultaneous failure of two
sections, which is a very low probability event, does not compromize
safety of the absorber core. For each section, current in the magnet
windings is supplied by a simple pulser that utilizes capacitor bank
discharge onto the windings. For each 4-meter section, capacitance
required to have oscillation frequency of 2000 Hz is about 20 μF. With
circuit impedance of 4 Ohm and resistance of windings at 2000 Hz of
about 0.1 Ohm, one can expect periodic discharge with a rather low rate
of current decay. If desired, it is possible to increase the decay rate
by adding some resistance to the circuit, it to ensure a better beam
current distribution through the dump block surface. Peak voltage is
about 8 kV, requiring about a 12kV rating on the windings and capacitor
bank because high reliability of the system is required. SCRs with
conservative ratings can be used at these values of voltage, current,
and repetition rate.

Depending on the final absorber block position, a certain amount of
vertically or horizontally bending dipoles may be wanted between the
Lambertson and the sweeping magnet. Each 1 mrad of bending requires 45
meters of conventional 1.5T dipoles . Thus the nominal position of the
dump should be chosen in conjunction with a worked-out scheme for the
Stage 2 extraction and abort channel, which minimizes the required bend
in both machines.

-   
-   
-   

References: *{ note---for Sec. 5.1.5 }*

\[1\] V.V. Kashikhin, I. Terechkine. \"Superconducting straight section
quadrupole magnet for low-field VLHC\", FNAL, TD-01-008, Feb. 2001.

\[2\] Conceptual design of the Superconducting Super Collider.
SSC-SR-2020, DE93 007234.

\[3\] J. Volk, Injection transfer line magnets. TD note \# TD-01-027,
FNAL, 2001

### 5.1.6 Magnet Production {#magnet-production .unnumbered}

Construction of the VLHC Stage 1 accelerator will require the
fabrication of several thousand magnets. The largest and most numerous
of these are the combined function arc magnets. They, along with the
dispersion suppressor dipoles, represent the majority of magnet costs.
They are also the most technically challenging as they are a significant
departure from existing magnet technology and, because of their extreme
length, require unique assembly procedures and facilities. All of the
other required magnets are variations of magnets previously produced for
other accelerators. They do not present any significant technical
challenge, as fabrication methods are well understood and a broad
experience base exists at various facilities within the labs and in
private industry. A breakdown of magnet type and quantities is shown in
Table 5.14.

Table 5.14. Magnets required for the VLHC Stage 1.

  ---------------------------- ------------------- -----------------------
  **Magnet Type**              **Physical Length,  **Quantity Required**
                               m**                 

  Main Arc Dipole              67.75               3136

  Dispersion Suppressor Dipole 48.8                160

  Straight Section Quadrupole  6.0 typ.            464

  Quadrupole, Large Aperture   10.0                10

  Low Beta Quadrupole          10.0                16

  Special Warm-Bore Magnets    Various             \~20

  Dipole Corrector             0.5                 3296

  Quadrupole Corrector         0.5                 3296

  Sextupole Corrector          0.8                 3296
  ---------------------------- ------------------- -----------------------

The extreme length of the combined function and dispersion suppressor
dipole magnets makes the fabrication process unique. The obvious
problems associated with the transport of these long devices make it
necessary for the final assembly of the magnets to occur in a building
strategically located to facilitate delivery of the completed and tested
magnets directly to the accelerator tunnel. Two production facilities
are envisioned. One facility will be located adjacent to the injection
transfer line with the other remotely located on the opposite side of
the ring. Magnet fabrication is projected to take place over
approximately six-years.

The facilities are considered assembly centers rather than manufacturing
sites. The magnet components will be fabricated off site at
subcontractor facilities to the highest level of completeness (value
added) possible, considering that the components will need to be
transported to the final assembly site. Constraints have been applied to
the maximum length of component parts and subassemblies so as not to
prohibit fabrication at remote locations around the country or overseas.
Twelve meters was chosen, as it is the standard for shipboard containers
and can easily be trucked over roadways without the need for special
permits and vehicles. The on site assembly facilities will do only that
work that cannot be done off site given the above constraints.

In any large-scale production program, a thorough quality assurance
program must be carried out during all stages of manufacture. Inspection
of parts upon receipt, testing of components where needed, and
statistical sampling techniques will be employed to ensure that
specifications are met. Warm magnetic measurements will be performed on
all magnets as part of the QA program. Cold tests will be performed on
all of the initial, low rate arc dipole production magnets and will
continue during full production at rates determined by the test
capacity. A discussion of magnet measurement and testing can be found in
section 5.1.7.

In this section we will concentrate on fabrication of the arc dipoles:
they are a cost driver and present some unique requirements, including
the superconducting transmission line. The facilities design, dominated
by the 65m length of the final magnet assemblies, is discussed first.
Factory throughput, labor required, and fabrication details associated
with the arc dipole magnet are then proposed. Fabrication of the iron
and structural assembly is discussed as well. Costs and schedules are
covered elsewhere.

#### 5.1.6.1 Production Facilities {#production-facilities .unnumbered}

The fabrication of the transmission line magnets (combined function and
dispersion suppressor dipole) takes place in two separate custom
facilities each with an approximate size of 210 meters by 140 meters. A
floor plan of the building is shown in Figure 5.27. Each facility has
three distinct areas; 1) component storage, 2) assembly and test, 3)
storage and staging into tunnel.

Component storage: The facility will be used as the terminus for
components fabricated off site. These components range from 12-meter
long iron core subassemblies to individual small parts. The space is
sufficient to house stock for at least three months of production. In
addition to bulk storage, space is allocated for staging (kitting)
components at the various assembly area stations.

Assembly and test area: The bulk of the facility is dedicated to magnet
assembly. There are fourteen "areas", each devoted to a specific step in
the fabrication process. Each fabrication area includes one or more
stations needed to achieve the required throughput for specific
operation. Each area will work autonomously and have the capability of
locally storing one week's production, so that glitches in one process
step do not immediately halt the production pipeline. The facility will
be manned 24 hours per day (three shifts) five days per week. Two shifts
(shifts 2 and 3) will do production at the assembly stations. One shift
(shift 1) will be used exclusively to move product between the various
stations, stage components at the stations and provide routine
maintenance. The output of each facility is one magnet per day. Table
5.15 lists each area, its function, number of stations required, and a
list of the tooling necessary to accomplish the stated function. A more
detailed description of the tooling necessary is included in reference
\[1\].

The factory will have special handling requirements. Since the magnets
and their subassemblies are 65 meters long, and will need to be
transported laterally between areas, no columns can be located within
the primary assembly area. A custom hoist system is required to lift and
transport the long subassemblies between the various assembly area
stations. Storage areas, associated with each assembly area, will be
needed to house finished subassemblies before moving to the next
higher-level assembly area. Most stations will require a staging area
where the various component parts for the day's production are
marshaled. Figure 5.28 shows, schematically, an elevation of a section
of the plant, showing the workstations in nine areas.

![](media/image26.wmf){width="5.986805555555556in"
height="4.492361111111111in"}

Figure 5.27. Transmission Line Magnet Assembly Factory Floor Plan

Storing and staging into tunnel: the completed and tested magnets will
be stored until they need to be transported into the tunnel. Magnet
installation in the tunnel is expected to take place at a peak rate of 4
magnets per day, significantly faster rate than the production rate.
Consequently, space has been allocated to allow a sufficient number of
completed magnets to be stored in preparation for installation. Support
stands will allow the magnets to be stacked vertically. A custom hoist
system (described previously under assembly and test area) will move the
magnets from the test stand to the storage space. An area is provided to
allow transfer from the storage area to a specially built transporter
rig (see section 5.1.8).

Table 5.15. Assembly area and tooling summary

![](media/image27.wmf)

![](media/image29.wmf){width="6.498611111111111in"
height="1.448611111111111in"}

Figure 5.28. Transmission Line Magnet Assembly Factory Elevation

####  5.1.6.2 Factory Throughput {#factory-throughput .unnumbered}

Each magnet construction factory is designed to produce one magnet per
day, accomplished in approximately 2 shifts. As with any normal
production scenario, initial throughput would be much lower than one
magnet per day, with the schedule eventually increasing to reach the
peak production levels.

Table 5.16 lists, for each area, the number of technicians and times
necessary to accomplish each operation, the number of technician-hours
required per day to manufacture one magnet, and the number of stations
needed in each area to complete the required tasks. All activities shown
in Table 5.16 are accomplished in two, 8 hour shifts per day.

Reference \[2\] shows detailed schedules for each sub-assembly
manufactured for the transmission line magnet, with a breakdown of times
elapsed for each individual operation described in section 5.1.6.3.
"Throughput" schedules for each work area are also shown.

Table 5.16. Technician resources required to produce one magnet per day.

![](media/image30.wmf){width="5.990972222222222in"
height="3.533333333333333in"}

At the end of each day, enough components or subassemblies are completed
in each area to produce one magnet. The subassemblies are stored on a
rack near each station after they are completed. A third shift is used
to move the components to the appropriate area of operation for the next
day's work. Maintenance of tooling is also done on the third shift or
weekends. Table 5.16 does not include these third shift activities.

#### 5.1.6.3 Magnet Assembly {#magnet-assembly .unnumbered}

Assembly of the arc dipole magnet for the VLHC Stage 1 accelerator is
summarized in this section. It is described in more detail in reference
\[1\].

##### A. Assembly of Drive Transmission Line for Stage 1. VLHC {#a.-assembly-of-drive-transmission-line-for-stage-1.-vlhc .unnumbered}

The transmission line consists of four components made by outside
vendors: inner tube sections, a superconducting braid, a copper braid,
and outer tube sections.

Mount 6, 12-meter long invar pipes together into one continuous section
at Area #1. Weld using automatic rotary welding heads, and inspect
mechanically. Tooling pulls the copper and superconducting braids over
the invar tube at Area #2. The outer tube is fed, in 12-meter sections,
over the assembly, then returned to Area #1 to be welded, then leak
checked at Area #5. The welded transmission line is moved to Area #3 for
ball swaging. 3 carbide balls, each of increasing diameter, are pulled
through the inner tube, swaging out the diameter and compressing the
braid between the two tubes. The line is moved to Area #4 for the
cryostat assembly. Support rings and aluminum thermal shield sections
are automatically fed onto the transmission line from the end. Trace
tubes for 60K helium are installed on the sides. 30 layers of
superinsulation are individually spiral wrapped onto the shield, while
the cryostat rotates on the assembly table. Tooling punches holes in the
insulation as it is being wrapped, to accept the penetrations from the
support rings. The extruded aluminum vacuum jacket is then fed over the
insulated assembly in 12-meter sections, returned to Area #1 and welded,
then leak checked at Area #5. The end of the drive conductor is bent
into a dogleg shape at Area #6. It is then moved to storage to wait for
installation into the iron at Area #11.

Assembly of the transmission line will require somewhat complex tooling,
which must perform seven types of automatic processes; automatic rotary
welding, feeding parts longitudinally onto pipes, pulling copper and
superconducting braid onto pipes, installing trace tubes, pulling
carbide balls through the assembly to swage the inside diameter, and
bending the line into the dogleg shape. Pictorial representations of
each of these processes are shown in reference \[1\].

##### B. Assembly of the Return Transmission Line  {#b.-assembly-of-the-return-transmission-line .unnumbered}

The return transmission line design is similar to the drive transmission
line, except a slightly larger size. The return transmission line is not
surrounded by an individual cryostat, as was the drive line. Instead, it
is included in the cryopipe assembly. Fabrication scenario is identical
to that given for the drive assembly, excluding the cryostat.

##### C. Fabrication of Cryopipe Assembly {#c.-fabrication-of-cryopipe-assembly .unnumbered}

Weld the 6.5K flow return pipes, the 40K shield supply header, and the
70K shield return header pipes together longitudinally in Area #1, and
leak check in Area #5. Transport the three pipes, together with the
Return Transmission line, to the assembly station Area #7 \[1\]. Mount
and align the four pipes. Feed 34 spiders over the pipes, spaced every
two meters. Attach shield sections. They are each two meters long, and
will clip on between each spider. Attach braids to intercepts from 4.5K
with connection to 6.5K. Apply superinsulation. Inspect, and transport
to storage area.

##### D. Installation of iron and structural support over the cryopipe assembly and transmission lines. {#d.-installation-of-iron-and-structural-support-over-the-cryopipe-assembly-and-transmission-lines. .unnumbered}

At Area #11 the Transport Drive Transmission Line and Cryopipe Assembly
are positioned in space using special tooling. The 12 meter long Iron
and Structural support subassemblies slide over the prepositioned drive
line and cryopipe assemblies, are positioned and attached.

When installed, the transmission line, complete with cryostat, needs to
be positioned with an accuracy of +/- ½ mm with respect to the iron
laminations. This will be accomplished by using a series of steel balls,
which will contact the outside surface of the transmission line cryostat
and fit into pockets stamped into the iron laminations. The balls,
cryostat, and iron laminations can easily be manufactured to a tolerance
acceptable to accomplish the accuracy necessary between the transmission
line and the iron. The specific tooling and procedure still need to be
developed, since this process was not used on the initial prototype.

Welds are then made at each junction between the magnet support tubes
(vacuum vessel). The vacuum vessel is leak checked, and the entire
assembly is inspected.

It is presumed that the iron and structural support subassembly,
including vacuum vessel, will be prefabricated in 12m sections in
industry and supplied to the final assembly site for assembly in the 65M
long magnet. As the accuracy of lamination profile and stackup are
paramount in achieving the design parameters some discussion is
warranted.

The pole tip profile is required to be reproducible to within 20
microns. While this tolerance is not achievable globally for all
features of the stamped laminations, manufacturing experience indicates
that it is possible for the limited range over which the pole surface is
defined. The laminations are to be stacked directly on the base datum
feature for the profile. This minimizes the tolerance buildup due to the
stacking operation. The design of the core assembly tie bars and welding
of the spacer bars to the laminations draw the laminations toward the
reference datum from which the profile is defined, assuring that the
basic dimension is maintained accurately.

The internal welding of the spacer bars to the laminations poses some
unique problems associated with physically fitting the required
automated welding equipment within the small space. Equipment will need
to be designed that fits within the limited space. A properly designed
apparatus will produce very repeatable results.

##### E. End Assembly {#e.-end-assembly .unnumbered}

Still at Area #11, connect drive transmission line shield cooling line
to 70K header. Assemble end components. Fit up and weld end vacuum
vessel. Leak check completed vacuum vessel.

##### F. Assembly of the beam tube and vacuum pumping chamber {#f.-assembly-of-the-beam-tube-and-vacuum-pumping-chamber .unnumbered}

Start at Area #8. Beam Tube sections are received in 12-meter long
extrusions. Two pieces must be seam welded together to make the final
assembly \[1\]. Inner and outer pieces are butt welded together into
68-meter long sections. Welds and interior surface quality is inspected,
while the assembly is still in two pieces. Getter pumps are installed
into outer piece. Then beam tube halves are connected and seam welded
longitudinally at Area #9. Leak check and beam tube bake out takes place
at Area #10.

##### G. Measurement of the magnetic field of the assembly. {#g.-measurement-of-the-magnetic-field-of-the-assembly. .unnumbered}

All magnets are measured magnetically: warm measurements will be
performed on all magnets while cold testing will be limited to a
fraction of the total production. Measurements must be done before the
beam tube and vacuum pumping chamber is installed, because the test
probe must be placed in the area occupied by the beam tube. Separate
stations are used for warm and cold testing and appropriate space has
been allocated in the facilities layout. A key concern is isolation of
the measurement area from sources of electrical noise which are
typically welding, electric motors, etc. The testing operation is
estimated to take 30 hours for a warm test and 70-80 hours for a cold
test, although this might be speeded up. More details on measurements
and testing follow in Section 5.1.7.

##### H. Installation of the beam tube and vacuum pumping chamber {#h.-installation-of-the-beam-tube-and-vacuum-pumping-chamber .unnumbered}

Beam Tube Assemblies are mounted onto Structural Support and installed
from the sides at Area #14. On half the assemblies, the beam tube must
be "sprung" into position, but then will stay in position after being
installed. On the other half, they will slide into position easily, but
will need to be secured afterward. The completed magnet is then
transported to the storage area to await installation into the tunnel.

#### References *{ note---for Sec. 5.1.6 }* {#references-notefor-sec.-5.1.6 .Reference-heading .unnumbered}

\[1\] J. Carson, R. Bossert, \"A Proposed Production Procedure for Stage
1 Transmission Line Magnets\", TD-01-028, 2001.

\[2\] J. Carson, R. Bossert, \"Throughput for Stage 1 Transmission Line
Factory\", TD-01-029, 2001.

### 5.1.7 Magnetic Measurements and Testing {#magnetic-measurements-and-testing .unnumbered}

In this section, we focus discussion on testing of the combined function
magnets during production since these magnets are the dominant element
of the Stage 1 machine. No doubt measurement and testing of other
magnetic elements in the ring are necessary, but most of these are of
more conventional design which can be accommodated by existing equipment
and approaches. Also because of their length and small bore, the
combined function magnets are the most difficult to measure.

Unlike 'conventional' superconducting magnets, the conductor of the
combined function magnets (transmission line) is not in a high field
region and quench 'training' is not a significant issue for magnet
performance. Thus magnetic field measurements dominate the magnet
testing process, both as a quality control measure and as
characterization necessary for machine operation.

Field measurements will be performed on all magnets. This must be done
before the beam tube and vacuum pumping chamber is installed, because
the test probe must be placed in the area occupied by the beam tube.
Roughly 10% of magnets will be measured with the transmission line
cooled to cryogenic temperatures allowing characterization of the field
to full current. The remainder will be measured with the transmission
line at room temperature. During initial stages of production when the
fabrication rate is lower, we will cold test all magnets. As rates
approach one magnet per day, the fraction of total magnets cold tested
will be determined by test facility capacity and test needs as indicated
by initial results.

We first discuss a conceptual design for a measurement system to be used
for the combined function magnets. We then follow with a brief overview
of the approach to cold testing and conclude with a few remarks on other
test and measurement considerations.

#### 5.1.7.1 Measurement System {#measurement-system .unnumbered}

As described above, magnetic measurements are the primary concern of the
test program. While one would also expect to perform an extensive series
of measurements, possibly using several measurement techniques, during
the R&D phase of magnet development, here we have chosen to present one
concept for measurements of production magnets. This concept utilizes a
rotating coil. We try to define the most important issues related to
this concept and examine the consequences. A brief discussion of other
approaches follows.

The main parameters of the arc dipole magnets are \~2 T field, ≤12%
horizontal gradient, 65 m length, and 20 mm gap. Measurement of the
integrated dipole field is needed with an accuracy of a few parts in
10^4^. Desired measurement accuracy for the higher order harmonics is
0.1 units.[^1] We begin by examining the implications of requirements
for field strength measurements. Based on this discussion we present a
concept for a measurement system. Given this system we then address the
issue of measurement of field harmonics.

With respect to measurement of the integrated field strength, there are
two issues. The fractional accuracy of the measured field goes as ∆*R/R*
where *R* is the radius of the rotating coil \[1\]. This requires that
the radius of the probe be known with high accuracy. Typical
manufacturing and measurement uncertainty for magnetic measurement
apparatus is \~0.001 inch (25 μm) which translates into a field error of
3e-3 for a probe of 10 mm maximum radius. At least an order of magnitude
greater precision (3e-4 strength error) is required. This level of
precision can only be achieved using a calibration magnet in which the
strength is known at least as well as one need know it in the subject
magnets.[^2] The second issue is unique to measurement of combined
function magnets. Due to the horizontal field gradient, an error in the
horizontal position of the probe translates into an error in measured
field strength. In a magnet with 10%/cm gradient, measurement of the
strength to 5 parts in 10^4^ requires positioning the probe with 0.05 mm
accuracy after averaging over the length of the magnet. Although
difficult, this can be achieved using mechanical fixtures referencing to
the magnet laminations. Vertical placement of the probe is not as
critical.

The main conclusions from the preceding discussion are that (1) a
rotating coil of the size we are considering can be calibrated with
sufficient precision, and (2) that the horizontal position of the probe
can be set with mechanical fixtures. For reasons we list below, we
choose to insert the rotating probe into the aperture from the side
rather than from the end. The probe is supported on a frame attached to
the magnet as shown in Figure 5.29. Principle elements of the design are
the following:

-   The probe body is clamped to a precisely machined fixture
    ('strong-back') on an edge which describes the magnet sagitta.

-   The strong-back slides horizontally in a series of guide brackets
    ('jaws ') attached to the vertical member of the frame. The
    strong-back is spring loaded so that it and the probe are forced
    against the magnet laminations at the edge of the magnet gap,
    referencing the horizontal probe position with respect to the
    laminations.

-   The vertical position of the probe is defined by the precision with
    which the frame is attached to the magnet and the precision of the
    jaws relative to the vertical member of the frame and the horizontal
    surfaces of the strong-back. A tilt sensor is mounted on the
    strong-back to monitor its alignment.

-   The motor for rotation and encoder for probe angle readout are
    mounted on the frame and connected to the probe by a mechanism such
    as a toothed belt or right angle drive. Other drive components could
    also be mounted outside the magnet bore (e.g. gearboxes).

-   Development of slip rings small enough to fit the probe bore is
    assumed although one might choose to digitize and transmit the
    signals from inside the bore. A pre-amplifier circuit sized to fit
    the bore is also assumed allowing a boost in signal size.

![](media/image31.jpeg){width="3.201388888888889in"
height="2.2319444444444443in"}

Figure 5.29. Measurement Fixture. Note that the magnet sagitta is highly
exaggerated.

A consequence of insertion from the side is that one loses a few extra
mm of probe radius due to the reduction in gap at the magnet edge of the
focusing magnet. One also needs to allow space for the clamps holding
the probe to the strong-back and for clearance during insertion.

Given a probe radius, we need to examine the accuracy of the measurement
of field harmonics. From \[1\] we see that probe calibration matters
little in measuring error harmonics. Accuracy of 10% or so is adequate.
This requires knowing the probe radius to 0.1%. What is of greater
interest is the evaluation of the interplay of signal size with harmonic
measurement. This has implications for the required level of excitation
current during test. For a reasonable set of probe parameters,
pre-amplifier gain of 100, measurement accuracy of 0.1 unit through n=9
requires at least 200 A excitation current \[1\]. This should be
possible for room temperature measurements. We would no doubt increase
the gain and run at the highest tolerable current for increased
accuracy. Hysteretic effects in the steel may be the limiting factor in
the measurement accuracy at this low field (\~70 Gauss, or 1/15 of the
injection field).

A probe length of 6.5 m was assumed above. Ten measurements are then
required to construct the integral field. The time required for
measurement is estimated as 2.5 hours with 2 crews of 3 technicians
using 4 sets of measurement apparatus \[1\]. This certainly allows for
the required production throughput. Automation and optimization of
procedures will reduce the time required. We also note that the
apparatus described could be used for either warm or cold measurements.
The only special consideration for cold measurements would be to
construct the strong-back of a nonmetallic material to prevent the
formation of eddy currents during ramping.

We have chosen a probe inserted in the magnet bore from the side and
supported by an external frame. An alternative approach would be a
\"mole\", such as have been developed for measurements of SSC \[2\] and
LHC magnets \[3\] which are probes with drive and angular alignment
systems built in. The obvious advantage of this approach is that the
probe can be larger by as much as 25% as insertion is from the magnet
end rather than the side. A larger probe produces larger signals.
However, development of drive apparatus operating in a strong magnetic
field is neither trivial nor cheap. We have no doubt that this could be
done; however, we have chosen a simpler approach that removes elements
of the measurement system other than slip rings and pre-amplifiers from
the bore accepting as a consequence somewhat smaller signals.

#### 5.1.7.2 Cold Testing {#cold-testing .unnumbered}

As a quality control measure and to characterize the magnetic field of a
sample of the magnets to full current, we plan to cold test at least 10%
of produced magnets. The peak rate of 2 magnets built per day requires 1
magnet cold test per week. As discussed in the introduction, quench
training is not a significant issue for the superferric design employed.
However, it is important to have a full set of field measurements of
magnets produced early in the program to check the overall design, iron
saturation, yoke fabrication, and related effects on the field quality
and transfer function. This increased testing also produces a
statistically significant warm-cold correlation for the field harmonics.
As the production rate rises, measurements check mechanical properties
of the magnets as well as properties of the materials used to build
them; and the set of measurements can be reduced to those necessary for
quality assurance.

The cold parts of the magnet are the transmission line and return bus
and their relatively small cryostat. Refrigeration requirements are
modest; cool down and warm up times, short. The associated test
equipment -- cryogenic end boxes, transfer lines, pumps, and
refrigerators -- is simple and inexpensive when compared to facilities
developed for testing 'conventional' superconducting magnets. Cold
testing can be done in a small area in the production facility in
conjunction with warm measurements rather than in a large, separate cold
test laboratory. The actual time spent in hooking up, cooling down,
testing, warming up, and disconnecting the magnet is small when compared
with conventional superconducting magnets. A peak production cold test
cycle occupying the test stand for one five day week would allocate a
two shift day to each of these tasks: installation and connection of the
magnet on the stand, cool down, testing, warm up, removal.

#### 5.1.7.3 Other Testing Considerations {#other-testing-considerations .unnumbered}

One of the difficult issues in design and construction of a magnet
system of the scale proposed is the understanding of its overall
reliability. Failure rates for the magnets must be very small if
collider availability is to be kept at the level necessary to carry out
the physics program. Determining failure rate is itself a difficult task
as it is unrealistic to plan for the number of tests necessary to
'prove' that the magnets as constructed will meet the lifetime
reliability requirements for the collider (even assuming that we could
agree on a 'proof'.) However, since the iron yoke design and peak fields
are similar to conventional magnet designs in use for decades, we do not
envision reliability problems here. Key components will be subjected to
'lifetime' testing -- equivalent magnetic and thermal cycles (if
appropriate) --to verify that they meet requirements. While it is
impossible to argue the statistical validity of a small sample of test
magnets, accelerated life testing of a few early magnets will be used to
validate design and provide feedback early in production should any
degradation in performance be detected.

####  {#section-11 .Reference-heading .unnumbered}

#### References *{note -- for sec. 5.1.7}* {#references-note-for-sec.-5.1.7 .Reference-heading .unnumbered}

\[1\] P. Schlabach, \"Magnetic Measurements during Production of VLHC
Low Field Combined Function Magnets\" TD-01-007, 2001.

\[2\] G. Ganetis, et al., \"Field Measuring Probe for SSC Magnets\",
Particle Accelerator Conference, 1987.

\[3\] L. Walkiers, \"Measurements for the Acceptance Tests of the LHC
Superconducting Magnets\', Eleventh International Magnet Measurement
Workshop, 1999.

### 5.1.8 Magnet Installation {#magnet-installation .unnumbered}

More than three thousand 67.75 m superferric magnets and their
associated subsystems must be installed in the arcs of the 240-km
accelerator ring. This installation must be tightly coordinated with
tunnel excavation, outfitting, and magnet manufacturing. The scale of
this work and the difficulty of subsequent maintenance require
techniques that ensure high quality installation resulting in high
reliability of the accelerator.

In addition, about 1000 conventional magnets (section 5.1.5) are to be
installed in the local straight sections and two transfer lines. This
installation is comparable to existing accelerators, nearby to surface
access, and less constrained by schedule.

The baseline assumptions adopted for the arc magnet installations are:

-   Beneficial occupancy of the tunnel takes place after the tunnel is
    dry and safe. Specifically, the excavation, muck removal, roof
    support, grouting, ventilation, sump installation, emergency egress
    systems, etc. should be complete.

-   The first installation activities complete the safety and
    transportation infrastructure. These include emergency and work
    lighting, communication, environmental safety monitoring, and
    trolley power lines for transport vehicles. At this point the tunnel
    can be used by workers without extraordinary training.

-   The second phase of installation provides infrastructure in advance
    of actual magnet installation. This includes magnet stands, power
    cables, quad electronics modules, Helium gas return header, and a
    sufficiently accurate survey and alignment network.

-   Magnets are transported into the accelerator tunnel one-by-one and
    installed onto pre-aligned adjustable support stands. The magnets
    arrive after a large amount of subassembly installation and test
    work has been completed at the factory. Specifically this includes
    transmission line and cryogenic pipe assembly and test, hi-pot and
    vacuum tests, vacuum system bake out, and cable installation and
    instrumentation checkout on the magnet (section 5.2).

-   Final installation of each magnet into the string involves: 1) rough
    alignment; 2) making the necessary interconnections for the
    transmission line, beam pipes, cryo-pipes and vacuum jackets; 3)
    installation of the skid containing the corrector magnets; 4)
    connection of the magnet cables to the electronics modules, 6)
    testing of the corrector supplies, instrumentation, and network
    readout , and 5) final alignment.

-   System checkout proceeds in phases. 1) a re-verification of the
    electrical network, high-pot test, and beam vacuum tightness is
    performed after each half-cell is assembled; 2) the insulating
    vacuum is tested after installation of each vacuum break (every 8
    magnets or 540m), a cryogenic performance and current load test is
    performed after each 10-km magnet string is completed

A basic constraint on the installation is that it be consistent with the
addition of the Stage 2 magnets at a later time. Because at the second
stage High Field Ring will modify tunnel layout, we must consider this
future collider upgrade while planning the mentioned above work so that
installed equipment wouldn\'t make this upgrade too complicated. Tunnel
cross section with both Low Field and High Field accelerators installed
is shown in Figure 5.30.

![](media/image32.wmf){width="2.716666666666667in"
height="2.7131944444444445in"}

Figure 5.30. Tunnel cross-section after the stage-2 upgrade.

#### 5.1.8.1 Tunnel Infrastructure Installation {#tunnel-infrastructure-installation .unnumbered}

Before magnet installation a number of systems must be completed.
Hangers must be mounted for the cable trays, transport trolley rail, and
the helium gas return header. Alignment requirements for these hangers
are in the 2-5 cm range and can be provided with the construction survey
monuments at quad locations, and stretched strings or lasers for the
intermediate brackets.

The baseline scenario uses manual labor and generic unit costs for
bracket and piping installation. However opportunity exists for
optimizing the process. Repetitive bracket installation could take place
with automatic drilling, installation, and bolting equipment. Long
sections of pipes, trolley rail, and cable trays could be preassembled
in the magnet factory and placed on these brackets with a long vehicle
and mechanical assists, thereby minimizing the number of in-tunnel pipe
welds, trolley rail joints, etc.

Cable laying required in the tunnel is minimized as described in sect
5.2.3.2. Long-distance (10km) power cable and optical fiber runs are
laid in a trench in the floor by pulling a trailer with a large spool.
Power and fiber connections to the electronics modules every are made by
unspooling long vendor-supplied harnesses with prefabricated breakouts
every 135m. Waxed-wire fire safety cables are suspended from trolley
rail hangers near the top of the tunnel.

The time at which electronics modules are installed and commissioned is
somewhat flexible. The modules should be functional by the time of final
magnet checkout so that they can be used to monitor insulating and beam
vacuum, temperature, etc. If they play an important role in tunnel
communications and environmental monitoring they should be installed
earlier. An early installation date encourages earlier system debugging,
but an electronics design frozen several years before project completion
will be painfully obsolete by the time of commissioning.

Prior to magnet installation, survey monuments must be embedded into the
tunnel wall to the sub-mm accuracy, and magnet support stands installed
and aligned to the accuracy of ± 1 mm in both transverse planes.

#### 5.1.8.2 Tunnel Transportation System {#tunnel-transportation-system .unnumbered}

An electric trolley system with rubber-tired vehicles is chosen for
transport of magnets and personnel. The system is similar to that
recommended for the SSC \[1\] and also chosen for the LHC transport
system \[2\]. An overhead enclosed safety rail \[3\] operating at
400-750VDC \[4\] provides power for magnet tractor/trailers, personnel
transport vehicles, and temporary power for installation work lights,
welding, etc.

The 30 ton magnet weight is less that the 35 ton LHC magnet so vehicle
power requirements are similar. Drive requirements are 30kW assuming a
total vehicle weight of 50 tons, a rolling coefficient of friction of
0.02 \[ref.1\], a drive train efficiency of 85% and a peak speed of
2.5m/sec (9 km/h). Trolley power up to 100kW is supplied at the 10km
alcoves, allowing up to three vehicles to operate simultaneously in each
10km sector. Copper conductors \~1cm^2^ are required in the rail to
limit line losses to \<10%. Details of the magnet transportation
vehicles are discussed in the next section 5.1.8.3.

In addition to the overhead rail, limited battery power allows the
vehicle to traverse unpowered regions such as splices and equipment
bypasses. The battery is continuously recharged during normal
operations. In emergency situations battery power is sufficient for the
transport tractor to drop the magnet and travel 5km to the personnel
egress points.

Personnel transport vehicles similar to \[1\] will provide emergency
egress, fire and ODH refuge, work break and sanitary facilities for
installation crews.

#### 5.1.8.3 Magnet Handling and Transportation Considerations {#magnet-handling-and-transportation-considerations .unnumbered}

Because of the unprecedented magnet length and flexibility, careful
attention must be devoted to their transportation to the place of
installation in the tunnel. Magnets will be handled and transported
using specially designed fixtures to prevent excessive stress
concentrations and damage.

Allowable limits on static deformation and torsion of the magnet are
shown in Table 5.17. In the three cases in the table, a force (or force
couple) was applied it to a single set of magnet support/adjusters while
the magnet cross section was held fixed +/-6m away at the position of
the adjacent magnet supports.

Table 5.17. Limits of relative displacement of magnet parts over +/-6m
length

+------------+------------+--------------------------------------------+
| Mode       | Allowable  | Limitation type                            |
|            | range      |                                            |
+------------+------------+--------------------------------------------+
| Horizontal | ± 3 mm     | Relative displacement of upper and lower   |
|            |            | magnet halves is more than 100 μm          |
+------------+------------+--------------------------------------------+
| Vertical   | ± 4 mm     | Stress in magnet structural elements       |
|            |            | exceeds ???% of yield limit                |
+------------+------------+--------------------------------------------+
| Twist      | ± 16 mrad  | Stress in magnet structural elements       |
|            |            | exceeds ???% of yield limit                |
+------------+------------+--------------------------------------------+
| Smooth     | \~1 km     | Stress in magnet structural elements       |
|            | Radius     | exceeds yield limit ??is this still OK??   |
| Bend       |            |                                            |
+------------+------------+--------------------------------------------+

Taking into account its length, the magnet structure is quite flexible.
Just due to its own weight, vertical sag can exceed the limits from the
table if one of the supports is removed. On the other hand, a smooth
continuous bend with 1km radius of curvature produces a 50cm sagitta in
the magnet with acceptable internal stresses. To significantly reduce a
risk of magnet damage during transportation, a 60m long aluminum frame
is used at this stage. The frame increases overall rigidity and protects
the magnet from vertical bending damage. Figure 5.31 shows the frame
moving inside the tunnel. Figure 5.32 shows the "A-Frame" structure of
the beam which permits it to be lifted or driven off the magnet.

![](media/image33.wmf){width="6.189583333333333in"
height="0.5770833333333333in"}

Figure 5.31. Magnet transportation frame, which acts as a "lifting
fixture" to uniformly support the magnet and prevent stress
concentrations during transport and installation. The frame is stiff
enough to allow the magnet to be picked up and supported at two points
without damage.

During transportation, dynamic loading effects have the potential to
increase stress levels in the magnet. During transportation and
installation, it is necessary to monitor and correct relative
displacement of magnet parts to the limits well below those of Table
5.17. This is accomplished with an active shock absorber system. Several
four-wheel carts installed along the frame use position controlled
hydraulic cylinders to support the frame with the magnet inside during
transportation. Inclinometers installed on the carts provide needed
information to a feedback system about relative position of the
neighboring carts. Accelerometers installed near critical points on the
magnet detect any mechanical oscillations and slow down or stop
transportation if any danger to magnet is suspected. Through the
coordinated action of the cylinders it is possible to lower the magnet
to its final destination in a controlled manner. This system is also
effective at limiting vertical deflections when the transportation
vehicle enters and exits the 4° slope of the installation ramp.

Two motorized trucks on both sides of the frame, each with engine power
of 60 kW and a typical operating power of 15kW, pull the frame during
transportation from production facility to the designated location in
the tunnel. An alternative chosen by the SSC & LHC is to use a
general-purpose towing tractor pulling a passive magnet trailer.

An automatic guidance system is desirable to reduce the chances pilot
error on monotonous drives through the tunnel. The simplest system can
use the overhead electric rail as a position reference. Another option
chosen by the LHC is to use the magnetic field of a guide wire buried in
a groove in the floor. Ultrasonic position detectors are commonly used
on mobile vehicles in factory automation. These require no tunnel
infrastructure and provide automatic shutdown if unexpected obstructions
are encountered. These have been successfully tested in robotic tunnel
guidance experiments undertaken as part of VLHC R&D at Fermilab \[4\].

#### 5.1.8.4 Initial Magnet Installation {#initial-magnet-installation .unnumbered}

The installation scheme shown in Figure 5.32 corresponds to the simplest
case when magnet installation occurs with a clear space upstream or
downstream of the installation point.

![](media/image34.wmf){width="5.988888888888889in"
height="1.3611111111111112in"}

Figure 5.32. Initial installation scheme which is possible when the
upstream or downstream magnet slot is empty. Installation vehicle a)
drives up to the location along the beam line, b) deposits the magnet on
the pre-aligned stands, and c-d) departs by initially moving along the
beam line, then moving if needed to the center lane to pass any
pre-installed magnets. Final connections e) may be made by separate work
crews working off-shift or in different sections of the tunnel.

*(this fig also needs to show side-by-side vehicle passing)*

Magnets are driven to their location along the beam line and put on the
support blocks without any transverse movement (Figure 5.32b). Unloaded
frames are then backed out along the installation pathway (c). In this
case, each next magnet can start its movement to the assembly place
without waiting for the unloaded frame and the transport vehicles. Two
magnet transport vehicles and an escape or a crew delivery vehicle can
move in the tunnel simultaneously and independently. This scenario
provides maximum flexibility for organizing optimal delivery traffic.

#### 5.1.8.5 Magnet Interconnections {#magnet-interconnections .unnumbered}

Three different types of interconnections are to be made after magnets
are installed. First, the two magnets in each half-cell must be
connected at the ¼-cell points to form a common electrical, cryogenic
and vacuum system. This is a "hard-welded" joint with no bellows in the
vacuum shell, cryogenic piping, or beam pipes. There is a 1-m space
available for this interconnection. Second, at the ½-cell points (Figure
5.11) the superconducting transmission line dog-legs downward into the
cryo service pipe enclosure to clear a 3.5-m space for conventional
correction magnets. Finally, in the straight sections where special
magnets are installed there is need for several modes of transmission
line positioning. The interconnection scheme does not differ greatly
among these cases; it is thoroughly described in section 5.1.2.3.4. The
basic steps of this procedure are listed below:

-   connection of the transmission line inner invar pipes for both
    active and return lines;

-   splicing of superconducting cables;

-   installation of electrical insulation and performing a high-pot
    test;

-   connection of cryogenic piping;

-   installation of a 50 K screen and superinsulation;

-   sealing and leak checking the insulating vacuum

Automatic welding machines will produce high quality vacuum tight
connections of all helium pipes. Appropriate fixture for the 100-kA
conductor splicing between the magnets must be designed and thoroughly
tested to guarantee 100% reliability for these connections. Magnet
interconnection appears to be the most labor-intensive procedure in the
process of magnet installation, so some R&D could profitably be devoted
to making this procedure simple. A high voltage test (5kV to ground) is
to be made for each magnet before final closing of the external vacuum
jackets of the interconnecting boxes.

(Do we want real splice pictures here to break up the theoretical nature
of this section???

#### 5.1.8.6 Corrector Magnet Skid {#corrector-magnet-skid .unnumbered}

In the baseline scenario, a skid containing six corrector magnets is
installed at the 3.5 m gap between half-cells (every other magnet or
135m). These magnets are factory assembled pre-aligned on common support
structure, with beam pipes, BPMs and bellows installed in the magnet
gaps. All correctors and beam instrumentation will be electrically
tested and cabled at the factory as described in section 5.2.3.2.
Description of the correctors can be found in 5.1.3. A total of 1568
corrector blocks will be transported and installed. A two-ton capacity
fork lift or equivalent hydraulic fixture will be used to install the
corrector magnet blocks on their support stands. The skids will be
aligned via locating pins in the previously aligned laminations of the
arc magnets. Then beam pipe interconnections can be made following by a
vacuum leak test.

Depending on the number of cryogenic problems encountered it may be
desirable to defer corrector and beam vacuum installation until
cryogenic system testing is completed.

#### 5.1.8.7 Magnet Replacement {#magnet-replacement .unnumbered}

A more complicated mechanical situation arises in the (hopefully rare)
situation that a magnet needs to be replaced after installation, or is
installed as the last magnet an otherwise complete arc. In this case the
magnet will be transported parallel to the magnets that have already
been installed (Figure 5.33 a; installed magnets are not shown). Using
hydraulic and control systems on the transportation trailers, the magnet
will be lowered down to temporary support stands installed beneath the
carts (b). After the frame is removed (c), the magnet is to be shifted
horizontally and placed on the permanent stands with the use of a
specially designed hydraulic pulling system connected to the permanent
support blocks (d, e). Control equipment similar to used during
transportation will synchronize the system during this operation. This
procedure will also be used to replace a Stage 1 magnet after Stage 2
installation is complete.

![](media/image35.wmf){width="5.988888888888889in"
height="1.4722222222222223in"}

Figure 5.33. Magnet replacement scheme.

Magnet replacement will require the following work at the magnet
interconnects:

-   Backfill the beam and insulating vacuum sectors with dry N2 and cut
    off beam pipes of the replaced magnet;

-   open the connection space;

-   remove super-insulation;

-   cut all the cryo-pipes and transmission lines of a the magnet to
    replace;

-   remove replaced magnet moving it horizontally out of the magnet
    string;

-   install new magnet following the repair scenario of magnet
    installation;

-   make interconnections as described above;

A reasonable goal for the magnet replacement procedure is to complete it
during one 8-hour shift of multi-crew work. Pump-down and leak checking
operations may extend this time. The overall magnet replacement time
will be dominated by cryogenic warm-up and cool-down.

#### 5.1.8.8 Arc Magnet Alignment {#arc-magnet-alignment .unnumbered}

During installation, the 65m magnet is bent in the horizontal plane to
the radial position predefined by the pre-aligned support stands. The
force necessary to establish the 1.5cm sagitta is less than 10kg. It is
assumed that support stand rough alignment is done with the help of a
semi-automated surveying system using available survey monuments in the
tunnel.

Arc magnets are ready for final alignment after correction magnets are
installed and vacuum pipe interconnections are made. Each magnet must be
installed so that the magnet reference center is within ± 0.25 mm from
the nominal orbit position. For each magnet, an acceptable roll angle is
less than 1 mrad RMS or less per adjuster. Conventional optical
techniques (theodolites and laser trackers) for alignment will have
angular errors in the range of 10 microns per meter, corresponding to ±
300 microns at the magnet ends from a setup at the center of the magnet.
This would be marginally adequate to meet the magnet alignment
specification of 250 microns RMS over the length of the magnet. However
this accuracy can be exceeded using the hydrostatic leveling and
stretched wire techniques described below.

For each magnet there will be a support every 6 meters with horizontal,
vertical and roll adjustment capability. The magnets will be built
"laser straight" in the factory. The magnets will be installed in the
tunnel with a 15.57-mm sagitta over the 65-meter length. The stiffness
of the magnet will allow an independent range of motion of approximately
± 3mm horizontally or vertically at each adjuster. Motions outside this
range will require coordinated movements of nearby adjusters. The magnet
position will be roughed in using optical techniques along the beam line
relative to the internal tunnel network. At each of the support stands
there will be a *hydrostatic leveling pot* for vertical alignment,
*capacitive stretched wire pick up* for horizontal alignment, and an
*electronic gravity sensor* for roll. As the adjustment screws are
turned there will be real time readout of both systems to allow for the
positioning of each segment of the magnet. A ± 3cm range of the
adjusting screws will be sufficient to put in the sagitta and to
compensate for installation errors in the magnet stands as well as drift
and settling of the tunnel (± 1cm maximum) over a 20-year lifetime.

**Vertical alignment** can be made using a hydrostatic leveling
technique, that makes use of fluid-filled containers with capacitive
readouts. This technique allows vertical alignment within ± 100 μm for
each magnet. For larger scale, corrections taking into the account
non-uniformity in Earth gravitation field must be made. This will
require careful study of the Geoid and the change in the density of the
earth in the region of the machine. Corrections to the vertical can then
be imposed on each magnet.

**Magnet roll** can be adjusted using the technique similar to used
during leveling of the magnets. It can help to establish a real time
display of the roll of the magnet at each adjustment station. Given a
base support of 500 mm and a resolution of 2 microns for the hydrostatic
levels a roll angle of ±4 micro-radians is achievable. This exceeds the
1 mrad requirement for acceptable vertical closed-orbit distortion.

**Horizontal alignment** is done using the stretched wire technique. A
small diameter (less than 1 mm) copper beryllium wire mechanically
attached to both ends of the magnet forms the reference base. Two wires
separated vertically can be used to increase the signal to noise ratio.
Using capacitive pickup electrodes at each support stand, it will be
possible to adjust horizontal position of each magnet to desired
accuracy. Alignment of the entire 66-meter magnet to within ±100 microns
should be possible. To set the sagitta of 15.6 mm for the magnet all the
adjustments must be made at the same time. Starting with optical tooling
the rough sagitta can be set to an accuracy of ±300 microns. Once this
is done the stretched wire system can be installed. Each capacitive pick
up will have a different offset from the magnet to account for the
sagitta. The final adjustment will involve moving all adjusters at the
same time.

A varying degree of automation is possible. The simplest approach is for
the person at the central display of magnet alignment data to give
directions to one or more workers with wrenches. A more sophisticated
alternative is to manually place motorized wrenches at each of the
adjusters, then run automated software procedures to bring the entire
magnet into alignment. If these systems were permanently installed and
coupled with motorized adjustment stands they could be used as an active
alignment that continually aligns the magnets as the machine runs. Beam
position monitor information could also be used.

#### 5.1.8.9 Straight Sections and Transfer Line Installation {#straight-sections-and-transfer-line-installation .unnumbered}

Special magnets of several types are to be installed in the ten straight
sections and two beam injection lines (see 5.1.5). Straight section
focusing quadrupoles and injection line dipole and Lambertson magnets
are conventional magnets. The maximum weight of these magnets does not
exceed 5 tons and their length is less than 6 meters, so they are
installed on their support stands using conventional techniques.

Separation/recombination dipoles and the abort Lambertson use the
transmission line for excitation. To minimize labor related to cryo
interconnections, these magnets are assembled in the tunnel by
installing steel magnet cores around preinstalled transmission line and
vacuum pipes. Individual pieces have lengths up to 6 meters and weigh
less than 5 tons. Dipole alignment is noncritical but the Lambertson
septa must be accurately aligned.

The third type of magnets is pulsed injection and abort kicker magnets
and abort sweep-magnet. These magnets are of dipole type, so
installation and alignment procedures for these magnets are
straightforward.

Finally there are eight 10-meter, superconducting, high gradient,
low-beta IR quadrupoles described in 5.1.4. Each quadrupoles will weigh
about 25 ton and is rigid enough to be transported to the place of
installation using two high load trailers and two transport vehicles of
the type used for the arc magnet transportation. The alignment
requirement for these quadrupoles installation is ±100 μm so two
adjustable support stands will be used. The alignment procedures are
complicated by the presence of the detectors and could be similar to
those used at the LHC.

Because sections that use special magnets are located closer to the
Fermilab and Far Side sites than accelerator\'s arcs, installation of
these magnet can be done independently of the installation of arc
magnets.

#### 5.1.8.10 Installation Schedule {#installation-schedule .unnumbered}

The number and size of working crews needed to install the magnet in a
3-4 year term has been estimated.

At least two access points at the opposite sides of the ring are
required. The simplest magnet delivery scenario can be realized when
assembly starts from the middle of the half-arcs connecting Fermilab
site and Far End site and goes to four directions simultaneously. If
magnet replacement is required after the magnet string is installed,
more complicated scheme must be used. In this case magnet traffic will
go down the tunnel with already installed magnets, and additional
measures must be taken to allow parallel work of an assembly crew. The
magnet installation procedure in this case also is more complicated
because it requires magnet movement across the tunnel.

Because of a high average magnet transportation length inside the tunnel
(about 30 km), only one magnet per day can be installed by each
installation vehicle. Several crews must work simultaneously to make
installation time acceptable. Connection of the installed magnets in a
string can be made simultaneously for several magnets.

#### 5.1.8.11 System Commissioning {#system-commissioning .unnumbered}

The described procedure will ensure interconnections of a high quality;
nevertheless, after each 20-km magnet string assembly is completed, a
cryo-test must be performed. This cryo-test will involve pressure test,
relieve valve setting tests, magnet string cooling down, heat leakage
test, and transmission line current test. Any possible cold vacuum leaks
could be detected at this point. The cryogenic plant performance and
magnet string quench test will be also conducted.

A temporary installation of the 100kA holding supply and current leads
(Figure 5.41) easily fits in the underground caverns eventually intended
for the Stage 2 dump resistors. The 2.5V holding supply will ramp a 20km
magnet string to 100kA in 40 minutes. This allows full-current testing a
complete quench protection cell of the accelerator.

The beam pipes are interconnected after the cryogenic test passes and
correction magnet block is installed. Because the system is not baked
*in situ*, the static vacuum will improve steadily over time and it is
desirable to have most of the system under vacuum for as long as
possible before storage ring commissioning.

References *{note -- for sec. 5.1.8}*

\[1\] Brown & Root Installation & Transport Proposal for the SSC

\[2\] LHC-HMU-CI-0001 Supply of Cryo-Magnet Transport Vehicles and
Unloading Equipment for the LHC Tunnel (from the CERN LHC Web site which
no longer has useful static links)

\[3\] An example of a commercial safety rail can be found at
<http://www.vahleinc.com/pdf/Catalog4C.pdf>

\[4\] Examples of tram systems and drive components operating in this
voltage range can be found at
<http://w4.siemens.de/ts/products_solutions/light_rail_tram>

\[5\] PAC 2001 invited talk.

## 5.2 Accelerator Systems {#accelerator-systems .unnumbered}

The systems are distributed around the ring circumference include
cryogenics, arc instrumentation, corrector power supplies, and beam
vacuum systems. The "once per turn" systems are located primarily in the
straight sections on the Fermilab site. These include RF, injection and
extraction, and once-per-turn instrumentation.

A completely conventional approach is taken to the standard utilities in
the straight sections. Warm iron/copper magnets use LCW cooling and
standard power supplies. Electronics and major power supplies are
located in underground shielded instrumentation rooms that are
accessible with beam on. A larger tunnel, conventional power systems,
and generous cable trays provide the infrastructure for RF systems,
injection and extraction kickers and Lambertsons, beam crossovers, beam
halo scraping, beam current and beam profile monitoring, etc.
Concentration of these major subsystems at the Fermilab site makes
maintenance and accessibility requirements similar to other Fermilab
accelerators. These systems are modeled on existing designs from recent
projects for which the specifications and costs are well known.

Four distributed systems contain notable new features which will be
described in some detail: the cryogenic system which is smaller and
simpler than comparable systems, the beam stop which must deal with the
large kinetic energy in the beam, the arc instrumentation which is
distributed as electronics modules in "holes in the wall" at each quad
location, and the beam damper system which is distributed around the
ring circumference.

### 5.2.1 Cryogenic System {#cryogenic-system .unnumbered}

#### 5.2.1.1 Cryogenic System Description {#cryogenic-system-description .unnumbered}

The magnet's superconducting transmission line is cooled by pressurized
supercritical helium at 4.5-6.0 K. The heat load of the magnet system is
removed by the sensible heat of the supercritical helium stream. The
fluid operates just outside the critical region expanding the helium
stream as it passes through the transmission line producing a large
effective heat capacity. The tunnel cryogenics are an all-piping system
with very simple topology.

![](media/image36.png)

Figure 5.34. Temperature profile of the supercritical flow in the VLHC
transmission line.

Cryogens are fed from six refrigerator plants spaced at 38 km intervals
around the ring. For efficiency reasons, refrigeration is provided at
two temperature levels. Refrigeration at a higher temperature range
(40-70 K) provides cooling for a heat shield that is used to intercept
much of the heat that would otherwise be absorbed by the lower
temperature superconductor. Each plant provides refrigeration for an
upstream and downstream magnet string 19km long. Each string is
sub-divided into two loops, referred to as "near" and "far" loops.

##### 5.2.1.1.1 Helium Distribution System {#helium-distribution-system .unnumbered}

The helium distribution system is designed to distribute refrigeration
to the magnet system with a minimal temperature variation. The
distribution system consists of cryogenic valve boxes, transfer lines,
and warm helium header.

###### (a) Cryogenic Valve Boxes {#a-cryogenic-valve-boxes .unnumbered}

Cryogenic valve boxes are used to redistribute the helium between the
conductor loops for steady-state operation and perform various transient
state operations. These boxes are located every 9.5 km and house the
control valves and instrumentation required for each circuit. Boxes vary
in configuration dependent upon location in the magnet string. These
boxes are relatively simple devices mainly providing a transition for
flow redistribution.

###### (b) Transfer Lines {#b-transfer-lines .unnumbered}

Transfer lines are a part of the magnet assembly. A line contains five
(5) circuits: 4.5 K superconductor supply line (near loop only), 6.0 K
superconductor return line, 40 K shield supply line, 70 K shield return
line, and a vacuum circuit. Each section of transfer line is equal in
length to a magnet (67.5 meters) and is attached to the magnet assembly
via a structural anchor at the midpoint of the magnet.

-   The 70 K return line is 0.102 m OD stainless steel pipe is connected
    to an extruded aluminum shield that surrounds all the inner lines.
    The shield is wrapped with a double-sided aluminized mylar (dimpled
    and perforated). The longitudinal contraction of the line is
    compensated with guided formed bellows in the interconnects. During
    this shrinkage, the G-10 support structure is allowed to move within
    the vacuum space.

-   The 40 K shield supply line is a 0.089 m OD stainless steel pipe
    supported on the G-10 spiders from the aluminum shield. Bellows are
    used at the end of each 67.5 m module to compensate for thermal
    contraction and expansion.

-   The 4.5 K supply (near loop only) and 6.0 K super conductor return
    line are Invar tubes which are also anchored at the midpoint of the
    module. These lines are of concentric design. The 6.0 K helium flows
    between two (2) concentric Invar tubes

-   The 4.5 K supply line is suspended via G-10 spiders from a 6.0 K
    inner line.

##### 5.2.1.1.2 Helium Pressure Relief and Venting System {#helium-pressure-relief-and-venting-system .unnumbered}

Relief valves for each of the five (5) circuits are located every 540
meters. These valves will vent into the warm helium header that is
itself protected every 1 km at 3 MPa (30 bar) from over pressurizing.
Each relief is conventional in nature and set to the MAWP of its given
circuit. The primary need for these reliefs are for trapped volume and
loss of insulating vacuum scenarios. The warm header is further
protected at the refrigerator (above ground) at a set pressure of 0.2
MPa (2 bar), venting to atmosphere.

![](media/image37.png)

Figure 5.35. Helium shield flow and pressure relief valves.

Quench protection of the transmission line is discussed in \[Koepke et.
al. & DR doc\]. The 100 kA transmission line conductor contains enough
copper that it can be safely shut down with a 1 second time constant
following a quench. A number of detailed quench simulations have been
performed. The peak temperature is \~250 K. The worst-case peak pressure
comes from a situation in which a mis-steered beam (kicker misfire)
causes the beam to oscillate side-to-side in the beam pipe and scrape
heavily in a series of locations separated by a half-betatron
wavelength. In this case the peak temperature is unaffected, but a
worst-case pressure occurs when the hydrodynamic shock waves from two
adjacent quenches collide at the midpoint between quenches. The peak
pressure is below the 4 MPa (40 Bar) pressure rating of the transmission
line. Thus no helium needs to be vented anywhere, even for a long period
following the quench. The pressure burst from the hydrodynamic shock
wave, as registered on pressure sensors along the transmission line,
could provide a convenient method of identifying where the quench
occurred.

##### 5.2.1.1.3 Heat Shield Cooling System {#heat-shield-cooling-system .unnumbered}

Pressurized 40K helium is used to intercept the radiation and conduction
heat leak to the transmission line. Helium is supplied from the
refrigerator at 1.7 MPa (17 bar) and returns at less then 70K and 1.3
MPa (13 bar). Flow is supplied via a 0.089 m O.D. tube and distributed
via a pair of 6E-3 m OD lines every 270 meters carrying 2.0 g/sec. This
scheme provides shield cooling for every two magnets. Control valves and
temperature sensors are included every 270 meters for heat shield flow
control based on temperature requirements.

##### 5.2.1.1.4 Transmission Line Heat Load Estimates {#transmission-line-heat-load-estimates .unnumbered}

Transmission line heat load estimates are divided into two (2)
components: the primary heat load on the 4.5K system and the heat load
to the 40K shield system. The calculated heat loads are presented in
Table 5.18.

Table 5.18. VLHC Design Study Calculated Transmission Line Heat Loads

![](media/image38.wmf)

##### 5.2.1.1.5 Power Lead Cooling {#power-lead-cooling .unnumbered}

Due to its low inductance (3uH/m) and low stored energy (15kJ/m), the
transmission line magnets require only a single 50V power supply and a
single set of 100kA current leads for the entire machine. The helium
consumption for these leads is estimated to be 5g/s for each lead. If
desired, this power requirement can be reduced by a factor of 4\~5 with
the use of High Temperature Superconductor (HTS) current leads.

##### 5.2.1.1.6 Refrigeration System {#refrigeration-system .unnumbered}

The refrigeration system is composed of six (6), 4.5kW @ 4.5K capacity
facilities equally spaced around the ring. Each plant will also provide
100kW of 40K refrigeration used in the shielding of the magnet system.

![](media/image39.png)

Figure 5.36. Cryogenic layout of Stage 1 VLHC. Six plants are spaced at
38km intervals around the ring. Each plant provides refrigeration
equivalent to 9.6 kW at 4.5K. Nominal operating wall power is 2MW at
each plant. One plant is on-site at Fermilab and has additional capacity
for detectors, IRs, and RF.

This provides approximately a 50% margin above predicted steady state
requirements. This margin is required to ensure continued operation when
the heat load increases either due to events such as a magnet quench or
vacuum leak, or because refrigeration capacity falls below its intended
design value (i.e. decreasing machine efficiency or inefficient heat
transfer due to contamination). With this scheme, all six refrigerators
must be operational for the accelerator to function. No plant redundancy
is built into this design.

Table 5.19. Predicted power requirements

![](media/image40.wmf)

The process helium is compressed from suction pressure of 0.101 MPa
(1.01 bar) up to an intermediate pressure of 0.4 MPa (4.0 bar) by means
of first stage compressor discharging into a second stage, which
compresses the helium to 1.85 MPa (18.5 bar). Turbo machinery is used
for the refrigeration plants while positive displacement machines
comprise the compressor system. There are two cold boxes: the upper and
lower cold boxes. Each cold box contains five (5) plate-and-fin type
heat exchangers and three expanders. To avoid return helium gas
instabilities due to the elevation change from the tunnel to the
surface, the lower cold box will be located at the tunnel level. This
requires a dedicated space of 432 m^3^ (6 m along the beam by 6 m
transverse by 12 m high) located near the accelerator tunnel.

![](media/image41.png)

Figure 5.37. Refrigeration Process Flow. A split cold box similar to LEP
is used to make the process insensitive to altitude changes between the
tunnel cryogenics and compressors on the surface.

These plants are well within the existing commercial vendor
capabilities. They contain no nitrogen pre-cooling. The cold box
configuration is a horizontal carbon steel shell enclosure housing all
heat exchangers, piping, valves, cold end of turbo expanders and vessels
operating at cryogenic temperatures. The equipment within the cold box
and the inner face of the vacuum jacket are covered by multi layer
aluminized Mylar. The cold boxes are designed to withstand the outside
atmospheric pressure while they are evacuated and are also protected
against overpressure by safety valves. All internal valves, filters,
turbo expanders, bayonets and major pipe connections are fixed at the
top plate and are accessible from a structural steel platform along the
length of the cold box. The turbo expanders are self activated gas
bearing superior in their performance to oil bearing turbines. Each
turbo expander is a small single-stage centrifugal turbine braked by a
direct-coupled, single stage centrifugal compressor. The turbine housing
is vertically mounted to a plate at the cold box top, projecting into
its vacuum space. Within the cold box are brazed aluminum heat
exchangers, pressure vessels containing and adsorbent to remove
impurities and the cold end of gas bearing turbo expanders. Part of the
outer shell cover is flanged and has an O ring seal, and is removable,
for complete access to all cold box internal components and piping. Two
panels will be mounted on the structural steel platform next to the cold
box. One containing all instrument terminations and transmitters, and
the other an assembly of purge and defrost valves. Provisions for
purification of the process helium is provided at each plant as well as
oil removal systems. A commercial control system package will permit the
unattended operation of these plants.

##### 5.2.1.1.7 Helium Compressor System {#helium-compressor-system .unnumbered}

The compression package will consist of three oil flooded rotating screw
compressors. One compressor will compress from 0.11 MPa (1.1 bar) to 0.4
MPa (4.0 bar), and the two other will compress in parallel from 0.4 MPa
(4.0 bar) to 1.85 MPa (18.5 bar). The first stage compressor is smaller
than the two (2) second stage machines. Each compressor skid contains
the compressor, main drive motor, oil reservoir/separator vessel, and
lubrication system mounted on a common rigid skid base. The base plate
provided is suitable for installation on a flat pad without grouting.
The helium enters the compressor and is compressed through the rotating
screw compressor, also flooded with oil. The oil seals the rotor and
absorbs some heat of compression. The compressed warm helium passes
through a water-cooled heat exchanger and then into a bulk oil
separator. The oil is also passed through a separate water-cooled heat
exchanger. Each compressor is direct driven by an electric induction
electric motor. The compressor assemblies are equipped with automatic
inlet and outlet block valves and automatic recycle valves.

The high-pressure helium from the compressors passes through a skid
mounted oil removal system. The oil removal system consists of three
stages of coalescing filter housings followed by a vessel containing
activated carbon. All entrained oil is filtered out of the gas stream by
the three stages of filters. The small amount of oil in the vapor phase
is removed by the activated carbon. The total amount of oil contained in
the helium leaving the oil removal assembly is less than 10 ppb .

##### 5.2.1.1.8 Helium Liquid and Gas Storage and Inventory Management {#helium-liquid-and-gas-storage-and-inventory-management .unnumbered}

The inventory for the entire cryogenic system is estimated to be 75 tons
of liquid helium, which is twenty (20) times the Tevatron inventory.
Each cryogenic plant will have three (3) 37.8 \[m3\] liquid helium
storage dewars, and fifteen (15) gas tanks capacity of 113.6 \[m3\].
This will provide 143 percent of the total helium inventory. The gas
storage serves as make-up/kick back during normal operations, and as a
buffer/storage during quenches and warm up of a single loop. The liquid
storage station will have pumps and heat exchangers necessary to
liquefy/warm up cold gas during upset conditions. During the planned
warm-up of the entire ring, the inventory will be liquefied into the
dewars. In case of a sector warmup, the inventory can be distributed
between five sector gas/liquid storage vessels via the cooldown header.
The tunnel transfer line and the cooldown header can be used to hold up
to 40% of inventory at pressure below the MAWP of any component in the
system

##### 5.2.1.1.9 Cryogenic Control System {#cryogenic-control-system .unnumbered}

A well-proven process control system will be used. The cryogenic system
in each sector will be controlled by a commercially available
distributed control system (DCS). Commercial program logic controllers
will be used for a local control of the cryogenic hardware in the event
that high-speed network connection is unavailable. The cryogenic control
system will provide full automation of any operation mode, including
transient modes. The accelerator high-speed network will be used for
communication and data exchange between sectors.

#### 5.2.1.2 Design Operating Conditions {#design-operating-conditions .unnumbered}

##### 5.2.1.2.1 Steady State {#steady-state .unnumbered}

Helium is supplied from a refrigerator at 4.5 K, 0.4 MPa (4 bar) and
returned at 5.8 K, 0.19 MPa (1.9 bar). Supercritical supply helium is
fed from the helium plant to four parallel loops. Each loop is comprised
of 9.5 km of magnet and transmission line. There are cryogenic
connecting boxes at the beginning and end of each 9.5 km section. At the
exit of the refrigerator the helium process is split into four (4)
paths. There are upstream and downstream magnet strings that are mirror
images of each other. The typical flow schematic of a magnet string is
shown in Figure 5.38.

![](media/image42.png)

Figure 5.38. Flow schematic of the 38km sector serviced by one cryogenic
plant.

As helium enters the upstream or downstream magnet strings the flow is
split into two parts: half enters the 4.5 K transmission line circuit
(for the near loop) and half enters the 4.5 K current return circuit
contained in the magnet (for the far loop). There is expected to be an
approximately 1 K gradient across each loop. These loop flows are then
re-distributed at valve boxes and become the return 6.0 K flow.

The cooling scheme relies on a balance between heat leak and pressure
drop. Any scenario causing an upset in the heat load (i.e. vacuum
degradation) can be compensated by increasing the helium flow rate and
supply pressure for the proper loop. The refrigerator has been oversized
by 50% to compensate for these types of upset conditions.

##### 5.2.1.2.2 System-Wide Purification {#system-wide-purification .unnumbered}

Purification of this machine will be done in two (2) steps. First each
sector will be pumped and backfilled five (5) times to 25 inches of
mercury via pump outs on every helium circuit at each valve box located
every 10 km. This method has been proven to work in the Tevatron. Levels
of contamination less than 100 ppmv are achieved with this first step by
using roughing pumps. The second step is dilution purification. A
purifier with a nitrogen cooled charcoal bed will be located at each
refrigeration plant. The discharge gas of the compressor system will be
circulated through this purifier and then will be distributed to the
magnet/transmission line system. Contamination instrumentation, such as
arc cells used on the Tevatron, will be used to monitor the ppmv levels
in each sector. The system will be ready for cool down when
contamination levels are \< 5ppm. It is estimated that the purification
for a sector in the VLHC will be 72 hours.

##### 5.2.1.2.3 System-Wide Cool down {#system-wide-cool-down .unnumbered}

Cool down of the VLHC will be done in three (3) stages. The first stage
involves the cool down of the helium plants. The second stage is the
cool down of the transmission line to 40K. Finally the transmission line
will be cooled done to operating temperatures.

In the first stage, cooling is provided by turbines and should not take
more than 24 hours per plant. In the second stage, the plant is setup in
the liquefaction mode and 40K gas at 0.4 MPa (4 bar) is sent via cool
down valves located at each valve box back to the compressor suction
warm gas header located in the tunnel. Gas flows from the refrigerator
into the warm header through the near loop transmission line, the 6.5K
return, and the current return circuits. When the temperature at the end
of the "near" loop (measured at the valve box) is 70K the flow is then
re-directed to the "far" loop and into the return header. As the "far"
loop temperature reaches 70K the second cooldown stage can be started.

During the second cool down stage the plant is re-tuned for an outlet
temperature of 4.5K. The flow pattern for the second stage is the same
as the first stage. As the temperature for each loop is at 7K the cool
down valves can be closed and the flow will be looped back in
refrigerator mode. Total cool down time is expected to be on the order
of 10 days.

### 5.2.2 Magnet Power Supplies, Current Leads, and Quench Protection {#magnet-power-supplies-current-leads-and-quench-protection .unnumbered}

Stage 1 power supplies are summarized in Table 5.20 below. The major
item is the single 100kA supply for the transmission line magnets. The
Interaction Region power supplies, current leads and quench protection
are discussed in sect 5.1.4. Total Stage 1 power supply requirements
(both ramping and steady state) are about a third of the Fermilab Main
Injector.

Table 5.20. Power Supply, Current Leads and Quench Protection Summary
for Stage 1 Machine

+----------------+------------+-------------+------------+------------+
|                | Tr         | IR          | Straight   | Corrector  |
|                | ansmission | Quadrupole  | section    | Magnets    |
|                | Line Power | Power       | Warm       | (warm      |
|                | Supply     | Supplies    | Magnet     | copper)    |
|                |            | (sect       | Power      |            |
|                |            | 5.1.4)      | Supplies   |            |
+----------------+------------+-------------+------------+------------+
| Number         | 1          | 2           | 16 approx. | 12,000     |
+----------------+------------+-------------+------------+------------+
| Location       | FNAL       | at          | Straights  | Quad       |
|                |            | Experiments |            | locations  |
+----------------+------------+-------------+------------+------------+
| Voltage per    | 62         | 10V typ.    | 1000V typ. | 100 Typ    |
| supply         |            |             |            |            |
+----------------+------------+-------------+------------+------------+
| Current per    | 100kA      | 25kA        | 200A typ   | 2A typ     |
| supply         |            |             |            |            |
+----------------+------------+-------------+------------+------------+
| Ramping MVA    | 6.2 MVA    | 1 MVA       | \-         | \-         |
| (tot)          |            |             |            |            |
+----------------+------------+-------------+------------+------------+
| DC Power       | 0.4 MW     | 0.6 MW      | 7.4 MW     | 2.1 MW     |
| (total)        |            |             |            |            |
+----------------+------------+-------------+------------+------------+
| LCW            | \-         | \-          | 150        | *(air      |
| Consumption    |            |             | liters/sec | cooled)*   |
+----------------+------------+-------------+------------+------------+
| Quench         | 1 Circuit  | 2           | \-         | \-         |
| Detection      | at PS      | ci          |            |            |
|                |            | rcuits/quad |            |            |
+----------------+------------+-------------+------------+------------+
| Quench         | Dumps @    | 4           | \-         | \-         |
| Protection     | 20km       | h           |            |            |
|                |            | eaters/quad |            |            |
+----------------+------------+-------------+------------+------------+
| SC Current     | 100kA-pair | 60kA-pair   | \-         | \-         |
| leads          |            |             |            |            |
+----------------+------------+-------------+------------+------------+
| **Peak Ramping | **17.7     |             |            |            |
| Supply Power** | MW**       |             |            |            |
+----------------+------------+-------------+------------+------------+
| **Total Power  | **10.5     |             |            |            |
| Supply**       | MW**       |             |            |            |
|                |            |             |            |            |
| **Power in     |            |             |            |            |
| Collision**    |            |             |            |            |
+----------------+------------+-------------+------------+------------+

#### 5.2.2.1 Main Transmission Line Power Supply {#main-transmission-line-power-supply .unnumbered}

The low inductance (3uH/m, 0.6H ring total) and low stored energy
(10kJ/m, 3GJ total) of the single-turn transmission line magnet allow
the entire ring to be powered from a single supply \[1\]. See Figure
5.39. A voltage of ±62V ramps the machine up or down in 1000 seconds.
The design current of 100kA at flattop exceeds the 90kA required for the
transmission line magnet to reach its design field. The supply will be
located on site at Fermilab in a shielded underground room approximately
25' x 50' TBD in size. The ramping power and footprint of the power
supply is comparable to one of the six Main Injector power supply
buildings. Superconducting current leads will be located immediately
adjacent to the supply to minimize power loss in warm buswork.
Superconducting buswork will carry the current through a short
connecting conduit to the transmission line magnets in a manner
identical to the MS6 test string \[2\].

![](media/image43.png){width="5.54375in" height="3.7958333333333334in"}

Figure 5.39. 100kA Power Supply and Quench Protection For Transmission
Line Magnets

The power supply is actually two supplies in series. The main ramping
supply generates the positive or negative voltage to transfers the
inductive energy into and out of the magnets. It is not used when the
magnet is at constant current. The second "holding" supply maintains the
current during long periods at flat top and injection, and provides only
the voltage necessary to overcome resistive losses in the current leads,
warm buswork, superconducting splices, and the shorting SCR switch
across the ramping supply. This approach minimizes the cost of the
ramping supply, simplifies the power distribution system, and moves the
tightest regulation and ripple requirements to the precision holding
supply.

The Main Ramping Supply design (Figure 5.40) is based on paralleling
8500A modules of design similar to Main Injector supplies. This approach
permits spare modules to be taken off line for repair, and allows the
use of commercially available 10kA DCCTs for current regulation. A
2-quadrant 12-phase SCR bridge returns inductive power to FNAL as the
magnets ramp down. Ramping systems are designed to have RMS power sized
to be halfway between the peak (6.2MVA) and the RMS (3.1 MVA). This has
proven to be a reliable design methodology for similar supplies at
Fermilab. The RMS feeder load of 4,800KVA is less than one feeder cable
for the source.

![](media/image44.wmf){width="6.5in" height="1.9520833333333334in"}

Figure 5.40. 100kA Ramping Supply Schematic (one 2 x 8.5kA module shown)

The +2.5V holding supply is essentially a copy of the 100kA switching
converter \[3\] constructed for the R&D magnet test. The device consists
of a 450VDC 500kW bulk supply followed by ten 10kA DC-DC converter
modules in parallel. This two-stage regulation scheme provides immunity
to variations in input line voltage. The modules use tape-wound cores
and Schottky power diodes. The switching frequency is \~2 kHz. To
minimize output ripple the 10 modules will be phased to switch
sequentially. This pushes the fundamental ripple frequency up to 10x the
switching frequency or \~20kHz. The switching will be phase locked to
the revolution frequency so that beam emittance growth due to power
supply ripple will be negligible. The control system for this switcher
will be integrated into that of the main ramping supply to simplify
regulation and load hand-off.

#### 5.2.2.2 Current Leads {#current-leads .unnumbered}

Superconducting current leads are required for both the main
Transmission Line and for the IR quadrupoles. IR quadrupoles can use
commercially available High-Temperature Superconductor (HTS) leads
similar to the LHC. The total current leads requirement for the Stage 1
machine is about 150kA-pair, or about 1/10 of the leads required by the
LHC \[3.5MA from Lynn Evans' stump speech\].

A single pair of 100kA current leads is required for powering the
transmission line. These could either be conventional copper leads
identical to the leads developed for the MS6 transmission line test
facility \[2\], or could be a specially built HTS version using the 50K
transmission line shield flow as the inter-stage temperature. The
cryogenic wall power associated with the conventional 100kA leads is
approximately 300kW. This could be reduced by a factor of 4 with HTS
leads \[4\]. Payback time for the electrical cost savings from HTS leads
is approximately 3 years.

![](media/image45.png){width="3.979861111111111in"
height="2.4305555555555554in"}

Figure 5.41. 100kA Superconducting Current Leads and switching
converters developed for the MS6 test string. A more compact arrangement
of the leads and power converter will be small enough to be placed in
the tunnel to be used for partial-ring commissioning.

#### 5.2.2.3 Quench Protection {#quench-protection .unnumbered}

The only superconducting magnets of the Phase I collider are the
transmission line magnets and the IR Quadrupoles. Protection of the IR
quads with heaters is described in section 5.1.4.

The low inductance and low stored energy of the transmission line magnet
allows a simple and inexpensive quench protection system. The magnets
themselves require no internal quench detection or protection circuitry.
Ring-wide quench detection is performed by a single circuit located at
the power supply terminals (Figure 5.42). Quenches are detected by a
voltage imbalance at the power supply (Figure 5.39). When a quench is
detected, magnetic energy is extracted with a 1-second L/R time constant
by cryogenic "dump resistors" spaced at 20km intervals around the ring.
This keeps the peak temperature and pressure in the quenched section of
the conductor at acceptable levels as described in section 5.1 Quench
protection system parameters are given in Table 5.21. The theory of
operation is explained \[5\] and a detailed write-up is given in \[6\].

![](media/image46.wmf){width="5.75in" height="1.8743055555555554in"}

Figure 5.42. Quench Protection Cell of the Transmission Line Magnet

The "dump switches" are deliberately quenched sections of transmission
line conductor built with Cu-Ni stabilized NbTi "switch wire"\[7\] which
is designed to have a high normal state resistance. Current is
transferred to a thick-walled Invar pipe which provides thermal mass.
These dumps are efficiently recooled using helium from the cryogenic
shield flows and transmission line flows, with the warm gas vented into
the return header.

The protection circuit for the 100kA current leads and power supply is
integrated into the quench protection system. When an overtemperature or
overvoltage is detected in the current leads, nearby copper buswork, or
power supply components, the power supplies are shut off and a ring wide
dump is forced. The required response time is equal to the thermal time
constant of the leads or approximately 100 seconds.

Table 5.21. Stage 1 Quench Detection and Protection Parameters

  ----------------------------------- -----------------------------------
  Transmission Line Current           100 kA

  Magnetic Stored Energy \@100kA      10 kJ/meter, 2100 MJ/ring

  Magnet Inductance at low field      3uH/m 600mH/ring

  Energy Dump Time Constant           1 second

  Peak Voltage To Ground during Dump  ± 3 kV

  I^2^t during dump                   5 x 10^9^ Amp^2^Seconds

  Peak Temperature of Conductor       250K
  During Quench                       

  Peak Pressure of Helium During      35 Bar
  Quench                              

  Pressure relief during quench       Every 2 cells (500m)

  Effective Copper Cross Section of   3cm^2^
  Conductor                           

  Quench Detection Threshold          1 Volt

  Quench Detection Method (primary)   Analog bucking with midpoint of
                                      current return bus

  Quench Detection Method (backup)    Deviation from V=LdI/dt at power
                                      supply terminals

  Energy Dump Resistance              60 mΩ per location,

  Dump Switch Locations               at cryoplants and midpoint of arc
                                      (20km spacing)

  Dump Switches                       Quenched superconducting cables 65m
                                      long

  Superconducting Dump Switch         1:1 CuNi:NbTi "Switch Wire"
  Conductor                           

  Cryogenic Dump Resistor Thermal     65m long x 20cm2 Thick Wall Invar
  Mass                                pipe

  Final Dump Temperature after Dump   325K
  from 100kA                          

  LHe Required for recovery after     1600 liters (less if shield flow
  Dump from 100kA                     used for pre-cooling)
  ----------------------------------- -----------------------------------

It is instructive to compare this quench protection system to those of
other accelerators. The LHC for example \[8\] requires a crate of quench
detection electronics in the tunnel underneath each dipole in the
tunnel. Each LHC magnet has more than 10 voltage taps and
instrumentation feed-throughs. The LHC also requires a much larger array
of energy dump resistors, dump switches, and current leads around the
circumference of the ring. Despite the larger machine circumference, the
quench protection system of the Stage 1 magnet is far simpler and should
be more reliable.

#### 5.2.2.4 Straight Section (Warm Magnet) Power Supplies {#straight-section-warm-magnet-power-supplies .unnumbered}

The straight sections use warm iron/copper quadrupoles and a small
number of other magnets. In each straight section all F and D
quadrupoles are powered in series by a single supply. The IR straight
sections have a larger number of independently programmable "tuning
quads" but the total power and LCW usage is approximately the same as a
normal straight section. The power supplies are located in shielded
rooms (one per straight section) which contain \~500kW of power supplies
and are accessible with beam on. These are single quadrant supplies.
Given the limited scope of these supplies it is desirable to make them
fully redundant, especially those at the far side of the ring from FNAL.
A detailed breakdown is given in \[Terechkine note\].

Dipoles and quad correctors magnets identical to the arcs are provided
at each quad location. Dipole magnets used to separate and cross over
the beams are powered by the 100 kA transmission line and require no
separate supplies.

Table 5.22. LCW and Power Dissipation Summary for Stage 1

+-------+-------------------+-----------+------------+---------------+
|       | **Heat Load**     | **Total   | **Total    | **LCW Flow    |
|       |                   | Loads**   | kW**       | (l/min)**     |
+-------+-------------------+-----------+------------+---------------+
| On    | Resistive Magnets | 188       | 4480       | 3200          |
| -Site |                   |           |            |               |
|       |                   |           |            |               |
| Str   |                   |           |            |               |
| aight |                   |           |            |               |
|       |                   |           |            |               |
| Sec   |                   |           |            |               |
| tions |                   |           |            |               |
+-------+-------------------+-----------+------------+---------------+
|       | Power Supply      | 22        | 500        | 600           |
|       | Cooling           |           |            |               |
+-------+-------------------+-----------+------------+---------------+
|       | RF Klystrons      | 16        | 3760       | 6400          |
+-------+-------------------+-----------+------------+---------------+
|       | RF Loads &        | 16        | 5600       | 4500          |
|       | Recirculators     |           |            |               |
+-------+-------------------+-----------+------------+---------------+
|       | Beam Stop         | 1         | 500        | 600           |
+-------+-------------------+-----------+------------+---------------+
|       | Total (on-site)   | 227       | 14840      | 15300         |
+-------+-------------------+-----------+------------+---------------+
| Far   | Resistive Magnets | 176       | 3320       | 3500          |
| Side  |                   |           |            |               |
|       |                   |           |            |               |
| Str   |                   |           |            |               |
| aight |                   |           |            |               |
|       |                   |           |            |               |
| Sec   |                   |           |            |               |
| tions |                   |           |            |               |
+-------+-------------------+-----------+------------+---------------+
|       | Power Supply      | 9         | 550        | 600           |
|       | Cooling           |           |            |               |
+-------+-------------------+-----------+------------+---------------+
|       | Beam Collimation  | \-        | 40         | 50            |
+-------+-------------------+-----------+------------+---------------+
|       | Total (far side)  | 185       | 3910       | 4150          |
+-------+-------------------+-----------+------------+---------------+
|       | **LCW Systems     | **412**   | **18750**  | **19150**     |
|       | Total**           |           |            |               |
+-------+-------------------+-----------+------------+---------------+

#### 5.2.2.5 Water Cooling (LCW) System {#water-cooling-lcw-system .unnumbered}

The "on-site" and "far side" straight sections require LCW systems. No
LCW system exists in the arcs. Major heat loads are the resistive
magnets, power supplies, and the RF klystrons. Loads are detailed in
\[Terechkine note\] and summarized in Table 5.22. The overall scope of
the onsite LCW system is comparable to the MI-60 LCW system of the
Fermilab Main Injector. The far site LCW system is about half that size.

The layout of the LCW system is sketched in Figure 5.43. The on-site
straight section is connected to the Main Ring LCW system and can use
the FNAL infrastructure for filling and makeup. Existing (unused) Main
Ring ponds exceed requirements for power dissipation. New ponds and
purification systems are required at the far side sites. The vertical
drop generates a 150 PSI pressure head which is overcome by locating the
circulation pumps at tunnel elevation and pumping the return flow
upwards. The beam stop and beam collimation cooling systems require
separate pumped loops for radioactive water (RAW) which will be heat
exchanged with the main cooling water flow to maintain isolation.

![](media/image47.wmf)

Figure 5.43. LCW System Layout for on-site Straight Section. The far
side LCW system is similar except that the RF loads are absent, the Beam
Dump load is replaced by the smaller load from the Beam Collimation
System, and an independent system of ponds and makeup water is needed.

#### References *{ed. note---for sec. 5.2.2}* {#references-ed.-notefor-sec.-5.2.2 .Reference-heading .unnumbered}

\[1\] Steve Hays, "*100kA Power Supply Options for the VLHC*", internal
note (unpublished).

\[2\] H. Piekarz et. al., "*Summary of Transmission Line Magnet R&D
Activities at MS-6*"

\[3\] G.W. Foster, S. Hays, H. Pfeffer, "*Design of a Compact 100kA
Switching Power Supply for Superconducting Magnet Tests*"

\[4\] J. G. Weisand (ed.), *Handbook of Cryogenic Engineering*, P.411

\[5\] Koepke/Mazur/Zlobin Snowmass '96

\[6\] GWF/Piekarz "Quench Protection of the Transmission Line Magnet",
VLHC note (unpublished)

\[7\] Switch wire is uses on persistent-current MRI magnets. Multiple
commercial sources include Oxford Instruments and Supercon.

\[8\] See the LHC PAC '99 papers. See also the proceeding of the
workshop on powering the LHC,
<http://lhcp.web.cern.ch/lhcp/TCC/PLANNING/TCC/Power2000/welcome.htm>

### 5.2.3 Arc Instrumentation and Power Distribution {#arc-instrumentation-and-power-distribution .unnumbered}

#### 5.2.3.1 Reliability and Maintenance Considerations in the Arcs {#reliability-and-maintenance-considerations-in-the-arcs .unnumbered}

The long arcs of bending magnets the have specialized and limited
requirements. The once-per-turn subsystems and their cabling, power and
cooling requirements are absent. No LCW system is required. Only the
repetitive instrumentation and corrector power supplies at each of the
1760 "quad locations" (every 135m around the ring at the location of
beta-max in each half-cell) are required. Infrastructure for power and
communications occurs at alcoves at 10 km intervals.

Reliability is at a premium for the arc instrumentation due to the large
size of the machine. Repair technicians at a centrally located facility
require a 20 mile drive to reach the surface facility and begin the
access into the tunnel. Travel time will not be small compared to the
1.5 hour time needed to refill the machine and reaccelerate the beams.
For this reason fully redundant capability is provided for all
mission-critical subsystems in the arcs. Power distribution is provided
to each module by two independent loop feeders with auto-resetting
circuit breakers and remote disconnects. Two independent power supplies
are provided for each corrector magnet and control function. Redundant
network connections to each module are provided. The critical function
of beam loss monitoring is provided by redundant sensors read out from
alternate quadrupoles modules. The system design is such that even the
death of a handful of quad electronics modules will not require
immediate maintenance.

![](media/image48.wmf){width="3.047222222222222in" height="2.275in"}
![](media/image49.png){width="3.1840277777777777in"
height="2.283333333333333in"}

Figure 5.44. Electronics module at each quad location (every 135m)
contains beam instrumentation and DC-DC Power Converters for corrector
supplies. Modules are in a radiation-shielded "hole in the wall" and
dissipate their power in the ambient tunnel air via a heat
pipe/thermosiphon and heat sink.

These electronics are located in a radiation-shielded modules buried in
"holes-in-the-wall" at each quad location. All cables for
instrumentation and corrector magnets are pre-assembled on the magnet
and factory tested before installation. Every other quad location (270m)
cryogenic thermometry and a valve controller are used to regulate the
50K shield flow. Every 10km there is a walk-in alcove associated with a
tunnel egress point that contains conventional electronics racks and
provides network connection, tunnel safety systems, bulk DC power for
the instrumentation modules, and cryogenic instrumentation for the
cooldown valve box. Average power dissipation is approximately 15 W per
meter of tunnel, which can be air cooled.

#### 5.2.3.2 Cabling in the Arcs {#cabling-in-the-arcs .unnumbered}

At the Fermilab Main Injector the cable tray to each service building
contains 316 cables with a total cable cross sectional area of 180cm^2^
\[1\]. Over 95% of these cables service Beam Position Monitors (BPMs),
Beam Loss Monitors (BLMs), ion pumps, corrector magnets, and temperature
and vacuum monitoring. The superconducting Tevatron also has a large
cable plant associated with quench protection and cryogenic monitoring
and controls. The installation, termination, and testing of these cables
are a significant cost and schedule item.

The Stage 1 design eliminates most cabling costs by multiplexing the
signals to a local electronics module (Figure 5.44) at each halfcell
boundary or "quad location". Signals are digitized locally and sent to
the control room via network fiberoptics. Instrumentation and corrector
magnets are clustered at the quad location and cable runs are typically
5 meters. Cable harnesses are prefabricated by outside vendors and
mounted on the magnets and tested in the factory.

![](media/image50.wmf){width="6.104166666666667in"
height="3.2305555555555556in"}

Figure 5.45. Cabling Layout on the Transmission Line Magnet. Cables and
instrumentation are preinstalled and factory-tested on the 65m magnets.
Each magnet has a 5m "extension cord" which jumpers to an electronics
module located in a hole in the wall at each quad location (135m
spacing).

#### 5.2.3.3 Corrector Power Supplies {#corrector-power-supplies .unnumbered}

The warm (air-cooled copper) correction magnets \[sect 5.1.3\] dominate
the power consumption in the arcs. The electronics module at each quad
location has 6-8 corrector magnet loads with a maximum installed power
of approximately 1400W. Average corrector power is \< 1000W in a
realistic operating scenario. At maximum current approximately 90% of
the power is dissipated in the magnets themselves with the remaining 10%
(\~150W) in the power supply converters. Instrumentation and control
power at each quad location is estimated to be \~100W for a total of
250W dissipated in the module. Power at this level can be passively
carried away from the electronics (Figure 5.44) via a heat pipe \[2\]
and removed by the tunnel airflow of \~1m/sec.

#### 5.2.3.4 Power Distribution in the Arcs {#power-distribution-in-the-arcs .unnumbered}

Redundant DC-DC power converters are provided both for module control
power and for each trim magnet. Power can be drawn from either of two
redundant 1kVDC feeders that loop the ring (see Figure 5.46). Power
supplies are connected in parallel at each load. Under normal
circumstances the load is shared and each power supply operates at \<
50% of rated load, encouraging long lifetimes. Under failure conditions
the load is taken over by a single supply which operates near its design
rating (or less, if the corrector magnet setting is below 100%).

![](media/image51.wmf)

Figure 5.46. DC Power Distribution Scheme in Arcs. Redundant Bulk DC
supplies in walk-in alcoves every 10km supply a redundant Loop Feeder.
Each local electronics module contains two DC-DC converters for each
load. Under normal conditions all supplies share loads and run at less
than 50% of rated capacity. By means of auto-resetting circuit breakers
(not shown), the system can tolerate short or open circuits on the loop
feeders, a failure of one or both bulk supplies at any alcove, a failure
of the AC surface feed to any single alcove, and individual failures on
many corrector supplies.

Medium-voltage 1kV DC is chosen for power distribution to the
electronics modules at each quad location. The DC is provided by 100A
bulk supplies every 10km located in racks of electronics in walk-in
alcoves. Two redundant bulk supplies are provided at each location, and
two independent distribution loops are provided to route the power to
the modules. Under normal conditions 25A is sourced in either direction
onto each of the 500 MCM loop feeders, and less than 3% of the power is
lost in the distribution cabling. Under fault conditions one or both of
the bulk supplies at one of the 10km locations can fail, with the slack
being taken up by adjacent supplies in the loop feeders. A short-circuit
fault in one segment of the loop feeders can be tolerated by letting its
circuit breaker trip and relying on the remaining loop feeder. Each
module is protected with fault current limiting via automatically
resetting "solid-state fuses"\[3\] .

The advantages of DC power in this application are as follows. The main
power consumption is due to corrector power supplies that naturally
operate as DC-DC converters. These are more compact than
line-transformer based supplies, an important consideration for the quad
electronics modules. Modern DC-DC converters \[4\] have the following
parameters: power density 200W/in^3^, efficiency \~90%, cost
\~\$0.35/watt. In fact, essentially all modern AC devices (fluorescent
light ballasts, computers, high current welders, motor controllers...)
rectify the AC line power then chop the signal using DC-DC techniques.
Rectification requires bulky capacitors and produces current spikes with
power factor and noise problems that complicate AC distribution. DC
power distribution makes the most efficient use of the copper in
distribution cables, which is a major cost component in power
distribution. DC power also simplifies the design of loop feeders, which
may be powered from separate segments of the power grid without regard
to the relative phase of the incoming AC power. Finally, by
phase-locking the switching frequencies of the DC-DC converters to a
frequency near the revolution frequency of the machine, noise effects on
emittance growth can be essentially eliminated as discussed in section
5.2.xxx.

#### 5.2.3.5 Beam Position Monitors (BPMs) {#beam-position-monitors-bpms .unnumbered}

Both X and Y BPMs (Figure 5.47) will be provided at each "quad location"
at half-cell boundaries between corrector magnets. This is twice the
number used in the Main Injector where it was determined that
measurement of the second coordinate only improved the closed-orbit
distortion by 10% \[5\] and only a single coordinate readout per quad
location was provided. However the added redundancy obtained by an
independent readout of both coordinates every half-cell will be
beneficial given the small aperture and the travel distance to repair
failed BPMs.

Button style beam pickups similar to those used on electron machines and
the LHC are adequate. These devices are nonlinear outside the central
30% of their aperture. Given anticipated closed orbit distortions \<1mm
this is not a problem. In a few special locations near beam transfers
where multiple off-axis orbits must be measured, split-plate BPMs with
better linearity will be used.

BPM readouts using either AM/PM or Log Amp electronics are acceptable.
In the case of Log-Amp readout both log(A/B) and log(A)+log(B) would be
digitized to provide both position and intensity readout. In the case of
AM/PM conversion a separate channel (possibly a log amp) is required to
provide intensity information. In either case an in-situ calibration is
desirable. The calibration circuit injects equal signals of adjustable
amplitude into both channels to accurately determine the zero-offset
response at different input strengths. A recent example of log-amp
readout made for the SLAC B-factory fit on a 2.7" x 4.7" board which
also included calibration circuitry \[6\].

Digitization bandwidth is determined by the first turn and transient
response desired. A digitization rate \>25MHz can be supported by the
DMA channels of today's DSPs, with no external components other than the
flash ADC. A 10-bit digitization of log(A/B) would provide 20μm least
count resolution. Power dissipation for 4 channels of 10-bit 40 MHz
digitization would be 300mW total \[6\].

The cable run from the BPM to the quad electronics module is about 5m.
This is long enough that the signal must be terminated but short enough
that normal RG-58 can be used. The cable runs are short enough that no
cable trimming for phase matching is required if AM/PM electronics are
selected.

![](media/image52.wmf)
![](media/image53.png){width="2.7958333333333334in"
height="3.203472222222222in"}

Figure 5.47. Beam Position Monitor (BPM) and Beam Loss Monitor(BLM) for
Stage 1 magnets. The BPM is a capacitive "button" style typically found
on small aperture beam pipes. The X&Y pickups are rotated by 45-degrees
to avoid the synchrotron radiation (this is common at light sources).
The BLM is a permanently sealed Argon filled cable-style ionization
chamber. Two redundant BLMs run the full length of the magnet. It
features all metal and ceramic construction similar to the Tevatron BLMs
to allow the device to operate unattended for years (no gas bottle to
change).

#### 5.2.3.6 Beam Loss Monitors (BLMs) {#beam-loss-monitors-blms .unnumbered}

The BLM function in the arcs is mission-critical in that no blind spots
may exist which might allow chronic beam loss to go undetected. We
therefore choose a cable style BLM which is essentially a long
ionization chamber that can provide complete coverage along the length
of the magnet. The cable will be all metal/ceramic construction (Figure
5.47) so that no gas-bottle changing will be required. For redundancy,
two independent cable BLMs are provided. Each runs the full length of
the magnet but they are read out at alternate quad locations. These
provide complete coverage even when the electronics module at a single
location goes *incommunicado*. Separate BLMs on each side of the magnet
provide some differential sensitivity to beam losses in each bore.
Electronics required include a 2kV/100μA Cockroft-Walton DC-DC converter
module, an op‑amp integrator, and a medium bandwidth \~100kHz 14-bit
ADC. Power dissipation should be \<2W.

#### 5.2.3.7 Ion Pump Power Supplies & Vacuum Gauges {#ion-pump-power-supplies-vacuum-gauges .unnumbered}

The electronics module for each 135m half-cell requires 12 ion pumps
(22.5m pump spacing in each bore). These are powered from the
electronics module. Each pump requires a 5kV supply with a starting
current of up to 30mA but an operating current less than 0.1mA. The
power for all 12 pumps is provided by single transformerless bulk supply
(a 5-stage Cockroft-Walton converter operating from the 1kVDC feeder).
High voltage DC relays (Cotto 5501) isolate each pump and give the
capability of providing the full starting current sequentially to each
supply. Individual current readback on each pump is provided via an
array of V/F converters operating at HV with an optically isolated data
link to the DSP.

Failure of the bulk supply shuts down all ion pumps in a 135m half-cell.
Pumping from the NEG strip remains intact. This results in a 50x rise in
the pressure of a single gas species (CH4) over the length of one half
cell, equivalent to a 3% rise in the average pressure of CH4 in the
ring. Redundancy in the ion pump power supplies is therefore
unnecessary.

#### 5.2.3.8 Network & Clock Connections {#network-clock-connections .unnumbered}

The electronics module at each quad location contains a Digital Signal
Processor (DSP) computer with an optical fiber connection running a
network protocol stack. This CPU can store, average, spectrum analyze,
and data-compress all digitized information before transmitting over a
conventional fiber network. A separate dedicated fiber handles the
FNAL-specific real time signals such as clock, event triggers, and beam
abort heartbeat signals. This will be handled in hardware logic by a PLD
in the electronics module.

A minimal set of fiber connection to each module consists of one network
connection plus one dedicated fiber for delivering Fermilab-specific
clock, event, and safety system signals. For cost estimation purpose we
have assumed four direct point-to-point fiber connections between each
quad location and redundant network hubs at located in the 10km alcoves.
The fiber cable will be a pre-assembled harness 5km long with 4-fiber
breakouts at quad locations every 135m. Installation will consist of
laying the fiber harness in the cable tray immediately below the
electronics modules (Figure 5.48) and plugging the breakout into each
electronics module.

![](media/image54.wmf)

Figure 5.48. Fiberoptic Clock and Network Connections in the tunnel
including redundant hubs & clock fanouts at 10km alcoves.

The long-haul fiber backbone interconnecting the 10km alcoves around the
ring will be buried with the power duct in the invert. This provides
additional radiation shielding to compensate for the longer distance of
the backbone fiber runs.

#### 5.2.3.9 Quad Electronics Module Miscellaneous Functions {#quad-electronics-module-miscellaneous-functions .unnumbered}

The networked DSP at each quad location provides the infrastructure for
additional features to be added at relatively low cost. In many cases
this requires adding only an interface IC, transducer and software to
the quad electronics module. The engineering effort for this is not
unreasonable given the large quantity of quad electronics modules. Some
possibilities:

-   Tunnel temperature, humidity, and airflow transducers.

-   Integrated radiation dose monitor for the electronics module (FET +
    resistor).

-   RF modules to communicate with the cell phones and PDAs of tunnel
    crews.

-   Microphones for detecting quenches, tunnel dripping, and goofing-off
    crews.

-   Speakers to communicate with the above.

-   Cryogenic sensors and valve controls (presently estimated as a
    separate system)

-   Vacuum valve controls (presently estimated as a separate system)

#### References *{ed. note---for sec. 5.2.3}* {#references-ed.-notefor-sec.-5.2.3 .Reference-heading .unnumbered}

\[1\] Fermilab Main Injector Technical Design Report, table 3.9.1.

\[2\] Your *{mine? I don't have one}* laptop computer probably has a
heat pipe in it. See <http://www.thermacore.com/papers.htm>

\[3\] Auto-resetting fuses are sold (for example) by:
[http://www.circuitprotection.com](http://www.circuitprotection.com/)

\[4\] Specifications quoted are single-quadrant DC-DC converters from
Vicor inc. [www.Vicr.com](../www.Vicr.com)

\[5\] Fermilab Main Injector Note #MI-75

\[6\] Medvenko & Smith, Beam Instrumentation Workshop 2000, p.503

\[7\] Specifications quoted are from
<http://products.analog.com/products/info.asp?product=AD9203>

### 5.2.4 Beam Vacuum System {#beam-vacuum-system .unnumbered}

The beam vacuum system is divided into two sections. In the 225km of
transmission line magnets an extruded-aluminum warm vacuum system
similar to LEP and electron storage rings is used. In the 8km of
straight sections synchrotron radiation is absent and the vacuum system
will be a conventional stainless steel system similar to those commonly
used at Fermilab.

![](media/image55.png){width="6.145833333333333in"
height="4.128472222222222in"}

Figure 5.49. Extruded Aluminum beam vacuum system in the transmission
line magnets.

#### 5.2.4.1 Arc Magnet Vacuum System {#arc-magnet-vacuum-system .unnumbered}

An extruded aluminum vacuum system (Figure 5.49) is used for the 225 km
of arc magnets (450 km of beam pipe) . The design of this system is
driven by vacuum desorption from synchrotron radiation, the small
aperture of the magnet gap, beam impedance and cost. Aluminum is chosen
for reasons of economy and beam impedance. The system is pumped by a
non-evaporable getter (NEG) strip located in an antechamber of the
extrusion. Methane and noble gasses are pumped by 10 l/s sputter-ion
pumps spaced every 22.5m. The antechamber dimensions are chosen to
provide adequate vacuum conductance to transport synchrotron-desorbed
methane to the ion pumps. Pump power and vacuum gauges are discussed in
5.2.3.7.

The parameters and performance of this system have been analyzed by
\[1,2\]. Inputs to the calculation included: 1) the measured
synchrotron-induced desorption of major gas species from aluminum \[3\]
as a function of the integrated dose of E~CRIT~ = 86 MeV photons, 2) the
measured pumping speeds for NEG strip as a function of absorbed gas
\[4\], 3) calculated conductances of the extrusion antechamber, 4) ion
pump speeds for methane, and 5) scattering cross sections for the
relevant gas species. This approach has given good agreement with the
measured performance of LEP \[5\]. The result of the calculation (Figure
5.50) is that a beam lifetime greater than 200 hours will be achieved
after approximately one week of operation. During the "beam cleaning"
period the beam current will be increased from an initial 50 mA to the
design value of 190 mA in five successive fills. The beam power
scattered into the cryogenic system (sect 5.3.3) will not be a limiting
factor during this time period.

![](media/image56.wmf){width="4.261805555555555in"
height="3.3645833333333335in"}

Figure 5.50. Beam Scrubbing Scenario for Stage 1 Aluminum Vacuum
Chamber. During the first 5 fills the beam current is increased from
50mA to the design value of 190mA. As synchrotron radiation desorption
cleans the walls of the beam chamber the vacuum lifetime increases to
\>200 hours.

Production of the aluminum vacuum system will be integrated into the
magnet factory. Tunnel labor is minimized by pre-assembling 65m lengths
of extruded pipe which are installed in the magnets, cabled, and tested
at the factory. Beam pipe extrusions 12m in length will be received,
inspected, and cleaned using an environmentally safe alkaline cleaning
procedure developed at the APS and used on the Fermilab Recycler \[6\].
The sections will be welded together to form 65m lengths which includes
the Ion Pumps, NEG strips and feedthroughs, and end transition sections.
The assembly will be sealed, pumped and baked at 200°C for 12 hours in a
65m long vacuum oven similar to the one built for the Recycler beam
pipes.

The vacuum pipe assembly is then snapped into the C-magnet gap (Figure
5.51) in such a way that the beam chamber is pre-loaded against the
magnet laminations. The preload prevents any possible loss of vertical
aperture inside the magnet. The beam pipe has to be deformed slightly to
get it inside of the horizontally focussing gradient magnet. This has
been analyzed \[7\] in ANSYS and stresses are acceptable even for
annealed aluminum.

![](media/image57.wmf){width="3.63125in" height="3.115972222222222in"}

Figure 5.51. Cross section of beam pipe extrusion inserted into the
magnet. During insertion the beam pipe is elastically deformed to fit it
into the gradient magnet.

The design does not provide for an in-situ bakeout. After factory
bakeout the magnets will be stored and transported with the beam pipes
capped off and under vacuum, and the beam pipes will be let up to dry
nitrogen and the caps cut off to make the field joints in the tunnel.
Under these circumstances an in-situ bakeout gains about a factor of 2
in initial dynamic outgassing \[8\], and gains very little after the
beam scrubbing has completed \[9\]. A similar conclusion has been
reached at the ELETRA light source \[10\]. Our R&D program should verify
this.

#### 5.2.4.2 Straight Section Vacuum System {#straight-section-vacuum-system .unnumbered}

Synchrotron radiation is absent or reduced in most of the 8km of
straight sections and the vacuum system will be a conventional baked
stainless steel / ion pump system similar to those commonly used at
Fermilab. The 10 cm aperture of the 135 m stainless steel pipes between
quadrupole locations is large enough that the beam impedance and vacuum
conductance are not a problem. The reduced apertures at the quadrupoles
and corrector locations will be handled with 30 cm funnel transitions
which may be copper-plated stainless or aluminum.

#### References *{ed. note---for sec. 5.2.4}* {#references-ed.-notefor-sec.-5.2.4 .Reference-heading .unnumbered}

\[1\] W. Turner "*Beam Tube Vacuum in Low Field and High Field Very
Large Hadron Collider*", LBNL-39482, UC414, presented at the Snowmass
Conference, CO, October 1996.

\[2\] M. Pivi and W.C. Turner , "*Beam Tube Vacuum in a Very Large
Hadron Collider Stage 1*", Version 2.1, 12 April 2001

\[3\] J. Gomez-Goni, O. Gröbner and A.G. Mathewson *"Exposure of a baked
Al lined stainless steel chamber to photons",* CERN, Vacuum Technical
Note 94-10 pg. 9, AT-VA/JGG.

\[4\] C. Benvenuti, *"Molecular Surface pumping: the getter pumps",* CAS
CERN Accelerator School - Vacuum Technology, CERN Yellow book, pg. 48.

\[5\] J.C. Billy, J.P. Bojon, O. Gröbner, N. Hilleret, M. Jimenez, I.
Laugier, P. Strubin, "*The LEP Vacuum System: a summary of 10 Years of
Successful Operation",* Proc. EPAC 2000.

\[6\] G.P. Jackson, "*The Fermilab Recycler Technical Design Report*",
FNAL-TM-1991

\[7\] I. Novitski, VLHC note on vacuum pipe stresses.

\[8\] A. Chao and Tigner*, "Handbook of Accelerator Physics and
Engineering",* pg.225

\[9\] Oswald Gröbner pvt. comm.

\[10\] A. Gambitta et al., "*Experience with Aluminum Vacuum Chambers at
ELETTRA*",EPAC 2000, Vienna, Austria, and J. Miertusova et al., "*How to
Save Money Designing a Vacuum System for a Third Generation Synchrotron
Light Source*," EPAC 1996.

### 5.2.5 Once-per-Turn Instrumentation {#once-per-turn-instrumentation .unnumbered}

A number of standard instrumentation systems occur only once per ring.
In general these can be copied from existing systems in the Tevatron
and/or Main Injector. The 53 MHz bunch structure and modest beam
currents (\~1/3 of Tevatron fixed target) provide no special challenges.
Readout electronics for these systems is located in shielded rooms at
the Utility Straight Sections. A warm beam pipe is used everywhere
except the IR triplet and superconducting RF cavities, so the
instrumentation interface is simple. Physical layout of these systems is
not heavily constrained since quadrupole spacing is typically 150m, the
beam pipes are separated by \~45cm for much of the utility straight
sections, and the transmission line and current return have been moved
away from the beam to reduce fringe field.

Table 5.23. Once-per-Turn Instrumentation Parameters

  ------------------------- ------------- --------------- --------------------------
  **FUNCTIONOccurrences**   **Readout     **Comments**    
                            Frequency**                   

  Tune Measurement          a few/ring    10 Hz           Use Arc Module DSPs for
                                                          FFT?

  Beam Current Toroids      1/ring                        Also on injection lines

  Sampled Bunch Display     1/ring        1 Hz             

  Fast Bunch Integrator     1/ring        1 Hz             

  Synchrotron Light Monitor 1/ring        1 Hz             

  Ion Profile Monitor       2/ring        .1 Hz            Small beam size may be
                                                          challenging

  Flying Wires              1/ring         \~few per       
                                          store           
  ------------------------- ------------- --------------- --------------------------

These are discussed more fully in:
<http://www-linac.fnal.gov/~mccrory/papers/VLHC_Controls>.

### 5.2.6 Radiofrequency Systems  {#radiofrequency-systems .unnumbered}

Either superconducting or warm copper cavities produce workable RF
acceleration systems for the stage 1 machine \[1\]. During the design
study acceptable parameters and costs based on the B-factory RF systems
were developed \[2\]. The system described here is based on
superconducting RF (SCRF). The advantages of SCRF are a higher energy
efficiency during the long periods at storage flattop, and more
flexibility to produce RF overvoltage to control beam instabilities if
this proves to be an advantage.

The RF system parameters and some RF relevant machine parameters are
summarized in Table 5.24. The RF frequency is 371.7 MHz, the seventh
harmonic of 53.1 MHz. Overall the VLHC RF system is similar to the LHC
RF \[3,4\], but with somewhat relaxed requirements to higher-order mode
damping due to lower total beam current. The superconducting cavities
are manufactured using niobium on copper technology developed at CERN.
As in the case of LHC, there will be separate RF systems for
counter-rotating beams. The beam separation in LHC is 420 mm. If we just
scale cryomodule dimensions with RF frequency, we get beam separation of
453 mm.

To minimize the effect of the transient beam loading, cavities with high
stored energy are preferred. The LEPII RF system experience \[5\] and
tests of LHC \[4\] and SOLEIL \[6\] cavities show that it is reasonable
to expect operating gradients as high as 8 MV/m. For VLHC we chose
gradient of 7.75 MV/m (3.125 MV per cell). Sixteen single-cell
superconducting cavities are needed for each beam in Stage 1 machine and
64 cavities are needed for each beam in Stage 2 machine. The low *R/Q*
of the LHC cavity helps to increase its stored energy. Still the large
(10%) beam gap will produce very strong periodic modulation of RF phase
of 27° for stage 1 and 10° for stage 2. This modulation is bigger than
at LHC. Special RF feedback loop around the amplifier-cavity system
assisted by the programmed phase modulation *a la* LHC \[7\] will be
necessary to suppress this effect.

Each cryomodule will accommodate four single-cell cavities with
cell-to-cell distance of 3λ/2. The overall length of the cryomodule is
approximately 5.6 m. Static heat leak of cryomodule is 60 W, RF cavity
wall losses is 55 W, which give us total cryogenic load of 280 per
cryomodule. Overall cryogenic heat load (without losses in cryogen
distribution system) is 2.24 kW for stage 1 and 8.96 kW for stage 2.

Due to rather small RF power per cavity we propose to use 500 kW
klystrons with 2 cavities per klystron in stage 1 and 8 cavities per
klystron in stage 2. The number of klystrons required is 16 for each
stage. A 500 kW CW klystron was developed and constructed recently
jointly by CERN and SLAC for testing LHC cavities \[8\]. The klystron
has high efficiency of 68% and thus required AC power is 735 kW to
generate RF output power of 500 kW. Then the maximum total wall-plug AC
power for klystrons is 11.76 MW per ring.

The klystron collector cooling water flow of ≥ 400 l/min gives us the
total amount of cooling water required to cool klystrons is 6400 l/min.
RF water loads will need additional 4000 l/min (during beam
deceleration) and ferrite circulators will consume 480 l/min. Thus the
total amount of de-ionized water required for RF system is 10,880 l/min
per ring.

To estimate cost of stage 1 cryomodules we will use formula \[9\]

$$C = k \cdot \left( 0\text{.}8 \right)^{\text{log}(L)}\sqrt{\frac{\text{1300}\text{MHz}}{f\left\lbrack \text{MHz} \right\rbrack}} \cdot L$$

Here *L* is the active length of accelerating structure, *k* = 200 k\$/m
is the cost factor. As one can see, the cryomodule cost scales
approximately linearly with total length of the RF structure. The total
cost of cryomodules for stage 1 is then equal to 4.2M\$. The RF chain
cost (including klystrons, high voltage power supplies, low level
electronics, and RF distribution) is \$1/W and totals to 8M\$.

VLHC RF system would greatly benefit from R&D on improving technology of
sputtering niobium on copper with the goal to decrease if not completely
eliminate phenomenon of the *Q* slope. Special efforts should be devoted
to understanding the nature of this effect. Success of this R&D would
allow increase of accelerating gradient without taking serious
punishment in the cryogenic heat load. Also, R&D program is required to
develop RF controls for heavy beam loading. Careful analysis of
transients during injection, acceleration and beam storing is necessary
and may necessitate having an individual klystron for each cavity \[4\].

Table 5.24. Summary of RF System Parameters

+----------------------+-----------+---+---------+-----------+----------+
|                      | **Stage   |   |         | **Stage   |          |
|                      | 1**       |   |         | 2**       |          |
+----------------------+-----------+---+---------+-----------+----------+
|                      | Acc       | S |         | Acc       | Storage  |
|                      | eleration | t |         | eleration |          |
|                      |           | o |         |           |          |
|                      |           | r |         |           |          |
|                      |           | a |         |           |          |
|                      |           | g |         |           |          |
|                      |           | e |         |           |          |
+----------------------+-----------+---+---------+-----------+----------+
| Beam current         | 190 mA    |   |         | 68.9 mA   |          |
+----------------------+-----------+---+---------+-----------+----------+
| Beam energy          | 0.9 -- 20 |   | 20 TeV  | 10 --     | 87.5 TeV |
|                      | TeV       |   |         | 87.5 TeV  |          |
+----------------------+-----------+---+---------+-----------+----------+
| Acceleration time    | 1000 sec  |   |         | 2000 sec  |          |
+----------------------+-----------+---+---------+-----------+----------+
| Acceleration per     | 14.8 MV   |   |         | 39.4 --   |          |
| turn                 |           |   |         | 18.15 MV  |          |
|                      |           |   |         |           |          |
|                      |           |   |         | (30.0 MV  |          |
|                      |           |   |         | av.)      |          |
+----------------------+-----------+---+---------+-----------+----------+
| Acceleration power   | 5.62 MW   |   |         | 4.134 MW  |          |
| (2 beams)            |           |   |         |           |          |
+----------------------+-----------+---+---------+-----------+----------+
| Synch. rad. loss per |           |   | 0.03    |           | 12.37    |
| turn                 |           |   | MeV     |           | MeV      |
+----------------------+-----------+---+---------+-----------+----------+
| Total s.r. power (2  |           |   | 13 kW   |           | 2.1 MW   |
| beams)               |           |   |         |           |          |
+----------------------+-----------+---+---------+-----------+----------+
| Revolution frequency | 1286.5 Hz |   |         |           |          |
+----------------------+-----------+---+---------+-----------+----------+
| Bunch length, rms    | 142 mm    |   | 66 mm   | 81.9 mm   | 33.7 mm  |
+----------------------+-----------+---+---------+-----------+----------+
| Synchrotron tune     | 0.00845   |   | 0.00179 | .00280    | .00189   |
+----------------------+-----------+---+---------+-----------+----------+
| Synchrotron          | 10.87 Hz  |   | 2.30 Hz | 3.60 Hz   | 2.43 Hz  |
| frequency            |           |   |         |           |          |
+----------------------+-----------+---+---------+-----------+----------+
| Bunch frequency      | 53.1 MHz  |   |         |           |          |
+----------------------+-----------+---+---------+-----------+----------+
| Number of buckets    | 41280     |   |         |           |          |
+----------------------+-----------+---+---------+-----------+----------+
| Bunch spacing        | 5.646 m,  |   |         |           |          |
|                      | 18.8 ns   |   |         |           |          |
+----------------------+-----------+---+---------+-----------+----------+
| RF harmonic number   | 288960    |   |         |           |          |
+----------------------+-----------+---+---------+-----------+----------+
| RF frequency         | 371.7 MHz |   |         |           |          |
| (7×53.1)             |           |   |         |           |          |
+----------------------+-----------+---+---------+-----------+----------+
| RF wavelength        | 80.65 cm  |   |         |           |          |
+----------------------+-----------+---+---------+-----------+----------+
| RF voltage           | 50 MV     |   | 50 MV   | 50 MV     | 200 MV   |
+----------------------+-----------+---+---------+-----------+----------+
| Accelerating         | 7.75 MV/m |   |         |           |          |
| gradient             |           |   |         |           |          |
+----------------------+-----------+---+---------+-----------+----------+
| Voltage per cavity   | 3.125 MV  |   |         |           |          |
+----------------------+-----------+---+---------+-----------+----------+
| *R/Q*                | 89 Ohm    |   |         |           |          |
+----------------------+-----------+---+---------+-----------+----------+
| *Q* factor at 8 MV/m | 2×10^9^   |   |         |           |          |
+----------------------+-----------+---+---------+-----------+----------+
| Number of cavities   | 32        |   |         | 128       |          |
|                      | (16+16)   |   |         | (64+64)   |          |
+----------------------+-----------+---+---------+-----------+----------+
| Cavities per         | 4         |   |         |           |          |
| cryostat             |           |   |         |           |          |
+----------------------+-----------+---+---------+-----------+----------+
| RF cavity wall       | 55 W      |   |         |           |          |
| losses               |           |   |         |           |          |
+----------------------+-----------+---+---------+-----------+----------+
| Cryostat static heat | 60 W      |   |         |           |          |
| leak                 |           |   |         |           |          |
+----------------------+-----------+---+---------+-----------+----------+
| Total cryogenic heat | 2.24 kW   |   |         | 8.96 kW   |          |
| load                 |           |   |         |           |          |
+----------------------+-----------+---+---------+-----------+----------+
| Beam power per       | 176 kW    |   | 0.406   | 42.4 kW   | 16.4 kW  |
| cavity               |           |   | kW      | peak      |          |
+----------------------+-----------+---+---------+-----------+----------+
| Number of 500 kW     | 16 (8+8)  |   |         | 16 (8+8)  |          |
| klystrons            |           |   |         |           |          |
+----------------------+-----------+---+---------+-----------+----------+
| Number of cavities   | 2         |   |         | 8         |          |
| per klystron         |           |   |         |           |          |
+----------------------+-----------+---+---------+-----------+----------+

#### References *{ed. note---for sec. 5.2.6}* {#references-ed.-notefor-sec.-5.2.6 .Reference-heading .unnumbered}

1.  V. Shiltsev, "*Summary of the Working Group II \\RF, Instabilities
    and Feedback Systems",* VLHC Accelerator Technology Workshop, TJNAF,
    Feb.1999. <http://www.vlhc.org/tjef/wg2_summary.pdf>

2.  A. Jackson, contribution to the VLHC Design Study, unpublished.

3.  The LHC Study Group, "The Large Hadron Collider -- Conceptual Design
    Report", CERN/AC/95-05 (LHC) (1995).

4.  D. Boussard and T. Linnecar, "The LHC Superconducting RF System,"
    *Proceedings of the 1999 Cryogenic Engineering and International
    Cryogenic Material Conference (CEC-ICM'99),* 12-16 July 1999,
    Montreal, Canada.

5.  P. Brown, et al., "Performance of the LEP200 Superconducting RF
    System," *Proceedings of the 9th Workshop on RF Superconductivity,*
    1-5 November 1999, Santa Fe, NM, USA.

6.  P. Bosland, et al., Completion of the SOLEIL Cryomodule,"
    *Proceedings of the 9th Workshop on RF Superconductivity,* 1-5
    November 1999, Santa Fe, NM, USA.

7.  D. Boussard, "RF Power Requirements for a High Intensity Proton
    Collider," *Proceedings of the 1991 Particle Accelerator
    Conference,* pp. 2447-2449.

8.  H. Frischholz, W.R. Fowkes and C. Pearson, "Design and Construction
    of a 500 kW CW, 400 MHz Klystron to be Used as RF Power Source for
    LHC/RF Component Tests," *Proceedings of the 1997 Particle
    Accelerator Conference,* pp. 2911-2913.

9.  H. Padamsee, "SRF for Muon Colliders," *Proceedings of the 9th
    Workshop on RF Superconductivity,* 1-5 November 1999, Santa Fe, NM,
    USA.

### 5.2.7 Beam Dampers  {#beam-dampers .unnumbered}

In the last 30 years high intensity storage rings have become absolutely
dependent on beam damper circuits. The Tevatron in fixed-target mode,
the Booster, and the LHC will not operate anywhere near design intensity
without them. At synchrotron light sources and B-factories the beams are
lost within milliseconds without dampers. It is thus not surprising that
the VLHC requires damper circuits to reach design luminosity for both
Stage 1 and Stage 2 operation. Fortunately this technology is well
developed. One new element which does occur in the Stage 1 VLHC is the
necessity to distribute the dampers for one type of instability (the
coupled-bunch resistive-wall instability) around the large circumference
of the ring. While this provides some level of redundancy (since the
beam is stable even if one of the distributed circuits fails) it is a
new element which will be described below. Other dampers are
conventional.

#### 5.2.7.1 Distributed Transverse Dampers for Resistive-Wall Stability {#distributed-transverse-dampers-for-resistive-wall-stability .unnumbered}

Growth of transverse motions of bunches in the LF ring will be
suppressed with active feedback systems. The strongest beam impedance
arises from resistive-wall. At the frequency of the first lower-sideband
coupled-bunch mode, which is (1-0.235)*f~0~* = 0.99 kHz, the transverse
beam impedance is (7.84+1.27j)10^10^ ohm/meter. This causes an
exponential growth rate of 2.53 x 10^3^ per second for a fully filled
machine. Prompt cancellation of this growth is provided by six localized
feedback stations spaced around the ring circumference. At each station,
radial and axial damping are the same and for each there are two
feedback systems displaced azimuthally by 270 degrees in betatron phase
to address both 'sine' and 'cosine' phases of the oscillation; this
makes the damping tolerant of changes of tune that might be desired.

![](media/image58.wmf)

Figure 5.52. Layout of Pickup and Kicker positions for the horizontal
coordinate at one station. Incoming beams with sine-like or cosine-like
oscillations have their positions sensed by pickups at cell boundaries
(F- locations) and are kicked back towards the design orbit after
one-quarter betatron oscillation. An identical set of vertical pickups
and kickers operates at D-locations. Six identical stations are
distributed around the ring, one at each stage 1 cryoplant location.

In localized feedback, a kicker is located downstream from the pickup by
90 degrees in betatron phase (one lattice cell) and the signal is
transmitted promptly from pickup to kicker through foam-insulated coax
to minimize delay. Delay in the 271 meters of cable is 180 ns to which
one adds about 50 ns. for electronic processing and amplification.
Although with this delay the signal from one bunch is delivered to the
12^th^ following bunch, the phase delay at 1 kHz is a negligible 1.5
milliradian. For higher-frequency sidebands the phase delay increases,
becoming a significant 1/8-oscillation at 550 kHz. The localized
feedback systems will be used up to 500 kHz; at that frequency the
impedance has become small enough to be controlled by a conventional
one-turn bunch-by-bunch system that extends up to the needed 26.5 MHz
bandwidth of coupled-bunch modes.

![](media/image59.wmf)

Figure 5.53. Electronic Elements of the Coupled-Bunch Feedback System.

The hardware in a local feedback system consists of (1) a pair of
capacitive pickup plates, (2) electronics and cable to the kicker, and
(3) a 4-meter long stripline-pair kicker. The pickup strips are 25 cm
long and connect to high-impedance amplifiers. The signals are then
differenced and the unipolar pulses are stretched to half the interval
between bunches to give a baseband signal for the kicker. At the lowest,
strongest mode, the required feedback loop-gain is *G* = 0.287 and to
damp injection errors of 0.1 mm calls for a transverse kick of 83.3 kV.
The kicker delivers this with a power input of 1.10 kW. Injection in
bunch trains separated by 2 seconds produces unwanted transients,
especially if there is closed-orbit offset. Bunch signals will be
recorded and analyzed to generate a correction for the local
closed--orbit corrector; this will zero the closed-orbit well before the
second train of bunches is injected. After the ring is filled,
additional rejection of very low frequency excursions will be made by
the low-frequency cutoff of the feedback electronics; this is possible
with baseband operation as we have here. For damping both radial and
axial motions at 6 stations, 24 systems are required for each
circulating beam.

Pickup and kicker are located at points of maximum betatron amplitude in
slightly modified standard arc cells. The modifications \[1\] involve
removing 5m of magnet iron at the boundaries of 8 successive half-cells.
An additional quadrupole corrector is used at each location to repair
damage to the β-functions caused by the missing focusing. The \~10%
dispersion wave generated by the missing bend automatically cancels
outside the insertion by virtue of the 360° phase advance across the 8
half-cells. The damper system uses at most 6 of the 8 available free
spaces. Placing the damper pickups and kickers where the dispersion is
nonzero is not believed to cause difficulties although this is will be
the subject of continuing study.

At the coupled-bunch mode frequency of 500 kHz, the growth rate has
reduced to 57 per second or 0.044 per turn. This and all higher
coupled-bunch modes are suppressed by the one-turn bunch-by-bunch
feedback system that operates over the range 53.1±26.5 MHz. The kicker
is a quarter-wavelength long at this frequency, 1.41 meter. The required
kick for 0.1 mm excursion is 26.4 kV and power is 513 watt. Power
amplifiers for this application are commercially available. The pickup
is the same length as the kicker and feedback gain is 0.108. Radial and
axial systems are similar.

One can ask if electronic noise in these dampers will add emittance
during a long collision time. Fortunately, although the loop gains are
high, the small aperture and peak bunch current of 8.4 ampere make the
pickup signal strong and large electronic gain is not needed. The peak
current gives a pickup sensitivity
$\text{IZ}_{L}\frac{g}{b}\sqrt{2} = 2\text{.}6´\text{10}^{4}$
volt/meter. Input thermal power with an amplifier noise figure of 1 dB
is 1.2*kTB* =5.2x10^-21^*B* where *B* is the bandwidth. Equating this to
the pickup signal power with equivalent rms noise amplitude *X~N~* gives
$X_{N^{2}}\text{>=}3\text{.}7´\text{10}^{- \text{28}}B$. The higher
energy at collision reduces the gain to G =0.013. The 12 feedback
systems would then cause an emittance growth rate, without allowing for
damping, of

$\frac{de}{\text{dt}} = \text{12}\frac{f_{0}g}{2\beta} < G^{2}X_{N^{2}}\text{>=}2\text{.}1´\text{10}^{- \text{17}}$
m/sec

Nominal emittance is 1.7x10^-6^, thus this dilution rate is of no
concern and would actually be smaller because of damping by the
feedback. The broadband system produces a similarly negligible emittance
growth.

#### References *{ed. note---for sec. 5.2.7}* {#references-ed.-notefor-sec.-5.2.7 .Reference-heading .unnumbered}

\[1\] J. Johnstone, Presentation to VLHC workshop in Lake Geneva, WI Jan
2001.

### 5.2.8 Injection {#injection .unnumbered}

The magnets and optics needed for 900 GeV beam injection are described
in section 5.1.5.4. An important design specification (not often taken
at Fermilab) is that the injection and extraction devices not present
any aperture limitation smaller than the arc magnets. This requires
full-aperture kickers and special large aperture copper/iron quadrupoles
in the vicinity of the Lambertsons. A high beta insertion minimizes the
strength of standard kickers required. The large aperture quadrupole is
described in section The magnet designs and layout in section 5.1.5.4
(for both injection and abort) meet that goal.

Transfer line magnet parameters based on both air-cooled copper and
permanent magnets have been developed. Either solution will require one
corrector magnet per quad location, with the power supply and
instrumentation in local modules similar to the arcs.

Beam is injected near the midpoint of the Utility straight section.
Downstream of this it will be convenient to have an internal beam
absorber for transfer line commissioning and tests independent of the
arc magnets. The injected beam, after passing through two quad locations
to measure position and steering errors, will be deflected 5-10 cm onto
the absorber by a standard corrector magnet. The scope of absorber will
be comparable to the Tevatron collider-mode abort. With reasonable
administrative intensity limits air-cooling should be sufficient. A few
bunches of 10^9^ protons are sufficient for a good BPM measurement.

## 5.3 Radiation, Machine Protection, and Beam Abort {#radiation-machine-protection-and-beam-abort .unnumbered}

### 5.3.1 Overview {#overview .unnumbered}

The 2.8 GJ of kinetic beam energy in the Stage 1 machine is
approximately eight times that of the LHC. Under normal circumstances
roughly 50% of this energy is gradually dissipated in beam-beam
collisions at the IRs. A few percent of the energy is lost diffusely due
to beam-gas collisions around the ring, intercepted by beam collimation
inserts which scrape away beam halo particles, and dissipated in the RF
loads as the beam is decelerated. Somewhere between 40% (intentional
beam abort at the end of the store at normal operation) and 100%
(unintentional beam abort at certain circumstances) of the beam energy
can be deposited in the external beam absorbers.

A very small fraction of the machine circumference exceeds the limit (\~
1 W/m of beam losses) for normal "hands-on" maintenance \[1\]. These
regions include the small-angle regions of the IRs, the beam collimation
system, and a small region or arc magnets downstream of the beam
collimation system. The average radiation load in these components is a
few times higher than the LHC, and the shielding and handling
requirements comparable. LHC experience will be useful in optimizing
these designs.

Under accidental conditions there is enough energy to cause severe
damage to the magnet and surrounding environment. This is not a new
situation for high energy colliders. The ISR beams had enough energy to
repeatedly burn holes in the machine \[2\]. The magnitude of the problem
has increased however. The beams of the Stage 1 machine carry enough
energy that in principle they could liquefy 400 liters of stainless
steel (whereas the LHC beams can only liquefy 50 liters).

Under worst-case accident assumptions the beam will leave the machine
and strike the tunnel wall. We have begun to study the mechanical and
radiological consequences. See section 5.3.3. A single shot beam
accident releases beam energy equivalent to losing the Main Injector
beam at one place for about 4 hours. This is not outside the scope of
existing shielding requirements at Fermilab, and should not be major
problem for a tunnel in deep bedrock.

Tunnel groundwater activation from single-pulse accidents appears not to
be a concern. A preliminary calculation indicates that it would be
possible to lose the beam in a single spot, immediately transfer the
activation into the tunnel water sump pit, and pump out the activated
water without violating applicable federal guidelines. Another way of
saying this is that you could dump the beam into the tunnel sump cistern
and the water would still be safe to drink. (This is of course an
absurdly pessimistic scenario, since it will take days or weeks for the
groundwater to collect in the sump, by which time most of the
radioactivity will have vanished).

Effective strategies have evolved to deal with machine protection issues
culminating with the Tevatron, SSC, and LHC. These issues have been
revisited for VLHC energies \[3,4\] and the results are summarized here.

Firstly, a robust and redundant extraction system removes the beam
whenever the position becomes unstable or anomalous losses are detected.
This protects the machine from anything which happens "slowly" (in
milliseconds to seconds) such as magnet quenches, RF or power supply
failures, vacuum failures or corrector magnet trips. Such a system has
prevented the Tevatron (so far) from having a hole burned through it.
This is a standard feature which continues to be essential at VLHC
energies.

The one credible accident which occurs on a rapid time scale involves an
abort kicker module misfire. The incompletely extracted beam will rattle
around the machine and hit various well-defined limiting apertures such
as extraction septa, IR quadrupoles, and beam collimators. The
probability of this will be reduced in the LHC by replacing Thyratrons
with solid-state kicker power supplies, and appropriate fail-safe logic
which in principle prevents a single module misfiring ("a partial-beam
abortion"?). Since the probability of this cannot be reduced to zero, a
set of "sacrificial collimators" are placed upstream of the vulnerable
components. These are replaceable graphite structures which absorb and
diffuse the beam energy at great personal cost. This strategy is
essential at the SSC/LHC and will be necessary and sufficient for the
VLHC.

Three qualitatively new features emerged while reviewing the machine
protection situation at VLHC energies. First, the graphite core of the
beam absorber may be damaged by a single pulse in the case of a sweeper
magnet failure. The core must be protected (sect 5.3.2.2) with a
replaceable sacrificial collimator immediately upstream. Secondly, in
the case of a sweeper magnet failure the beam window in the extraction
channel will have a hole melted in it. This is not a safety issue, but
in this accident scenario the beam vacuum must protected with an
automatically closing gate valve and the window(s) must be replaced.
Finally, the beam collimation system (sect 5.2.3.4) will require water
cooling for the jaws of the secondary collimators.

### 5.3.2 Beam Abort System {#beam-abort-system .unnumbered}

#### 5.3.2.1 Extraction {#extraction .unnumbered}

It turns out to be quite straight forward to kick the beams out of the
machine towards absorbers. The magnet parameters and layout are
discussed in section 5.1.5.4.2. Like the Tevatron, SSC and LHC abort
systems, we use fast kicker magnets to switch the circulating beam into
the other aperture of Lambertson magnets. The circulating beam goes
through the field-free hole in the Lambertson magnets, and the extracted
beam is bent upward in the Lambertson magnets so as to clear the first
quadrupole in the downstream half of the straight section. A full
aperture extraction kick is used and the separation of the circulating
and extracted beams is 25 mm at the entrance to the Lambertson magnets.
Thus any beam which is circulating anywhere in the physical aperture
will be extracted. Special large-aperture warm-iron-and-copper
quadrupoles are used near the Lambertsons so that no aperture
restriction is presented to the circulating beam.

Normally the beam extraction is synchronized with an "abort gap" in the
beam which is equal to the rise time of the extraction kicker. During
certain control system failures it may be necessary to unconditionally
extract the beam. This sweeps the beam across the extraction septum
which must survive without damage. For the VLHC the stress on the
extraction septum is roughly equal to the LHC (since the beam energy per
unit time is similar) and does no damage.

The requirements for the reliability of a one-turn extraction mechanism
are comparable to the SSC \[5\] and LHC \[6\]. The extraction kicker is
broken into 10 independent modules, with any 7 out of 10 sufficient for
a safe abort. Solid-state pulsers (as opposed to Thyratrons) will be
used to minimize accidental prefires. Three Musketeer logic
("All-for-one, and one-for-all!") guarantees that any single module
firing will automatically trigger the rest of the modules.

Figure 5.54. Schematic layout of Beam Abort channel including kickers,
Lambertson septa, extraction beam sweeping, beam defocusing, beam
window, sacrificial rod, and 4-in-1 Beam Absorber. Under normal
circumstances the extracted beam is swept in a spiral pattern to spread
the energy across the graphite dump. If the sweeper magnet fails, the
beam travels straight ahead into a sacrificial graphite rod which takes
the damage and must be replaced.

#### 5.3.2.2 Beam Absorber {#beam-absorber .unnumbered}

For TeV beams, the natural choice for the absorber is graphite, as at
the Tevatron, SSC and LHC. The major difficulty lies in making the beams
big enough that they will not crack a graphite absorber. A standard
absorber consists of a graphite core, contained in an aluminum jacket
with water cooling, followed by adequate steel and cement to protect
ground water. The graphite core is rectangular, with dimensions 10 ×1.2
×1.2 m. The thickness of steel shielding around the aluminum container
is about 1.3 m on each side and extends about 3 m downstream. At present
we consider a "4-in-1" design where extracted beams from both directions
hit absorber cores in a common sarcophagus. The Stage 1 and Stage 2
machines share a common absorber for each direction.

Activation and cooling water considerations are driven by the average
beam power on the target. The 500kW average power (corresponding to one
full-energy abort of both beams every 12 hours) is comparable to the
300kW design value for the Main Injector beam absorber. The overall
design is patterned on the Main Injector absorber which has proven
satisfactory and meets ES&H requirements for this power level.

The graphite dimensions and beam size necessary to contain the showers
without cracking the graphite were found by detailed simulations with
the MARS14 code. The design goal was to keep the maximum temperature
rise at the axis of the graphite core per spill below 1300-1500°C (from
successful Tevatron dump experience and theoretical shockwave
considerations). For a purely Gaussian beam with a spill that is
stationary in transverse position, the beam sigma would need to be 19 cm
in both x and y for the maximum temperature rise in the core of 1330°C.
Expanding the beams to this size with defocusing quadrupoles is out of
the question.

##### 5.3.2.3 Beam Sweeping System {#beam-sweeping-system .unnumbered}

A spiral beam sweeping scheme similar to the SSC and LHC is adopted to
spread the beam energy across the absorber core. Magnets are described
in 5.1.5.4.2. A horizontal and a vertical sweeper, 90° out of phase,
both oscillate with decaying amplitudes. Ideally the frequency should
increase as the radius of the spiral decreases in order to keep the
temperature rise constant. Since this is electrically difficult a
suitable compromise is to limit the inner radius of the spiral to half
that of the outer radius and accept a factor two higher temperature rise
at the inner radius. An estimation indicates that an outer radius of 30
cm would be adequate to keep the temperature below 1500°C. If the beam
sigma was 0.5 cm in both planes, the frequency of these sweepers would
be 9.7 kHz.

In the case of a failure of both coordinates of the sweeper system the
beam would damage the graphite absorber core \[7\]. To prevent this a
sacrificial graphite rod 5 cm in diameter and 4 m long is positioned on
the beam axis immediately upstream of the main absorber. See Figure
5.54. Normally the extracted beams will spiral around this rod without
hitting it. If the beam is extracted with all sweeping magnets off, the
beam damage will be confined to the sacrificial rod. The rod will be
housed in a metal box to prevent the spread of radioactive debris.

A beam window will not be protected in case of sweeping system (or
defocusing quadrupole) failure, if the effective beam sigma on the
window is less than 0.5 cm. The ring vacuum can be preserved by
rapid-acting gate valves and/or multiple windows in series. Each window
gets a small hole drilled in it when the sweepers fail, and pumping
between the windows isolates ring vacuum until a slow gate valve closes.
Alternatively, differential pumping with several wire meshes would do
the same job.

![](media/image60.png){width="3.0416666666666665in"
height="1.2777777777777777in"}

![](media/image61.png){width="3.140972222222222in"
height="0.6583333333333333in"}

![](media/image62.png){width="2.8006944444444444in"
height="1.1631944444444444in"}

![](media/image63.png){width="2.536111111111111in" height="1.15in"}

Figure 5.55. Beam sweeping system optics. Left: 3-sigma beam half-size
at 1 TeV injection (beam size at 20 TeV is 4.5x smaller), and beam line
layout. Right: beam displacement with respect to the direction of
extraction straight section and maximum sweeping kick in the horizontal
or vertical plane.

### 5.3.3 Radiation and Beam Loss {#radiation-and-beam-loss .unnumbered}

#### 5.3.3.1 Quenches from Beam Loss in Transmission Line Magnets {#quenches-from-beam-loss-in-transmission-line-magnets .unnumbered}

The warm-iron design of the Transmission line magnet is less sensitive
to radiation-induced quenches than ordinary superconducting magnets. To
determine tolerable beam loss in the arcs, MARS14 simulations are done
in the lattice both at injection (1 TeV, σx,y = 1.4 mm, α*~inc~* = 0.7
mrad) and top energy (20 TeV, σx,y = 0.3 mm, α*~inc~* =0.15 mrad).
Corresponding materials and magnetic field distributions have been
implemented into a 3-D model. Inward and outward beam losses were
considered both for inner and outer beam pipes (see Figure 5.56).

![](media/image64.png){width="3.0805555555555557in"
height="2.5861111111111112in"} ![](media/image65.wmf){width="2.2125in"
height="2.5597222222222222in"}

Figure 5.56. Beam loss geometries simulated in the Stage 1 VLHC magnets.

Simulations show that the superconductor in the transmission line
magnets is rather well protected radially by warm iron. The energy
deposition is diffuse and the peak temperature is relatively low at the
hottest spot in the showers downstream of where the proton hits the beam
pipe. Therefore, the tolerable beam loss is significantly higher than in
a conventional cosine-theta type magnets. Table 5.25 shows fast (1 msec)
and slow (0.1 sec) beam loss rates needed to initiate a SC magnet
quench---assuming the same quench limits as in the Tevatron SC dipoles
--- at injection and top energy in the Stage I ring. For comparison, the
values for the Tevatron at 0.9 TeV are shown. The assumption that the
temperature needed to incite a quench in both magnets is identical is
probably pessimistic since the braided cable of the VLHC can re-route
the current around a quenched region on the magnet midplane but a
cosine-theta magnet cannot.

Table 5.25. Quench-Inducing Loss Thresholds for the VLHC Stage 1 and
Tevatron

  ------------------------ ------------------------ ----------------------
                           Fast Loss Protons/pulse  Slow Loss Protons/sec

  0.9 TeV                  9 ×10 ^8^                3 ×10 ^9^

  20 TeV                   2.5 ×10 ^7^              7.5 ×10 ^7^

  Tevatron                 4 ×10 ^7^                3 ×10 ^8^
  ------------------------ ------------------------ ----------------------

#### 5.3.3.2 Cryogenic Heat Load from Beam Losses {#cryogenic-heat-load-from-beam-losses .unnumbered}

Heat load from beam-beam interaction debris in the IR quads is included
explicitly in the discussion in section 5.2. The cryogenic heat load
from beam loses in the arcs is also a potential concern. At 20 TeV
roughly 5% of the energy from beam losses is estimated to be absorbed in
the cryogenic transmission line. If 1% per hour of the (3+3) GJ of beam
energy were lost uniformly in the arcs, this amounts to a total heat
load of 800 W (3.5mW/m average) which is a 5% perturbation on the 5K
heat load. The collimation system (section 5.3.4) is expected to
localize essentially all beam halo losses into collimators in warm
sections, thereby eliminating that heat load from the cryo system.

The collimation system will be ineffective against losses from inelastic
beam-gas scattering. With the expected vacuum lifetime (sect 5.2.4.1) of
\>200 hours, the cryogenic heat load will be \< 2mW/m, less than 3% of
the 4.5K heat load. If continued R&D reduces the 4.5K heat leak this
will become an increasingly important part of the total.

#### 5.3.3.2 Radiation Damage to Tunnel Electronics {#radiation-damage-to-tunnel-electronics .unnumbered}

The Section 5.2.3 describes electronics housed in small enclosures
("holes in the wall") at each quad location. This approach was studies
at UNK \[8\] and the electronics was found to survive under rather
conservative assumptions about their radiation hardness. A recent
interesting development \[9\] is that modern CMOS is found to be
intrinsically rad-hard due to the absence of long-term charge trapping
at the gate oxide layer in sub-micron devices. The LHC is apparently
contemplating placing unshielded electronics under each dipole, and is
initiating a study of the radiation hardness of commercially available
electronics \[10\]. Depending on LHC operational experience, the rather
modest costs of the module enclosures might be saved by eliminating the
enclosures. Or not.

Radiation damage to fiber optics placed in the tunnel is was studied at
the SSC \[11\]. It was found that placing the fibers into the trough in
the invert guaranteed their survival even for upgrades to 10x the SSC
luminosity. We have followed this approach (section 5.2.3.8).

### 5.3.4 Beam Collimation System  {#beam-collimation-system .unnumbered}

Even in good operational conditions, a finite fraction of the beam will
leave the stable central area of accelerator because of beam-gas
interactions everywhere along the accelerator, intra-beam scattering,
collisions in the IPs, RF noise, ground motion and resonances excited by
the accelerator imperfections continuously produce a beam halo. As a
result of beam halo interactions with limiting apertures, hadronic and
electromagnetic showers are induced in accelerator and detector
components will cause accelerator related background in the detectors,
magnet heating and accelerator and environmental irradiation. The design
strategy of the VLHC is that the beam losses are controlled as much as
possible by localizing them in a dedicated beam collimation system. This
minimizes losses in cryogenic parts of the accelerator, and drastically
reduces the source term for radiation hazard analysis in the rest of the
lattice. The technology for these systems has been well developed for
the Tevatron, SSC, and LHC.

For the VLHC a complete beam cleaning system which provides for both
betatron and momentum scraping has been designed and simulated
\[12,13\]. The three-stage beam collimation system consists of 5 mm
thick primary tungsten collimators placed at 7σ~x,y~ and 3 m long copper
secondary collimators located in an optimal phase advance at 9.2σ~x,y~
and aligned parallel to the circulating beam envelope. Two more
supplementary collimators are placed in the next long straight section
to decrease particle losses in the low-β quadrupoles and in the
accelerator arc. They are located at 14σ ~x,y~ to intercept only
particles scattered out from the secondary collimators.

![](media/image66.png){width="2.654861111111111in"
height="3.5868055555555554in"}

Figure 5.57. Beam loss distribution along the accelerator at injection
(top) and at collisions (bottom).

![](media/image67.png){width="2.638888888888889in"
height="3.5395833333333333in"}

Figure 5.58. Beam loss distributions in the collimation section at
injection (top) and at collisions (bottom).

The simulated performance of the system meets the goal of essentially
eliminating losses away from the cleaning insert. A main reason for this
excellent performance is that the system uses a purpose-built lattice
insert rather than a something which has been retrofit into an existing
machine such as the Tevatron. The maximum beam loss in the arc section
behind the collimation region () is 1 W/m in two 21.5 m long dipoles and
one 6 m long quadrupole, and 0 .2 W/m in two 21.9 m long gradient
magnets.

The effect of beam cleaning system operation on the particle loss
distribution in the entire machine was design and calculated with
emphasis on reducing losses and detector backgrounds near the high
luminosity insertions. But in our calculations, with 6 ·10^4^ particles
lost in the collimators, we did not see any loses in the vicinity of
interaction point. Further investigations should be done to determine
particle backgrounds in the IP from the collimation system.

The primary collimation insert will be located in a far side straight
sections conjugate to the on-site Utility Straight Sections. Secondary
collimators will be located in this section as well as in special
locations near the IRs. The secondary collimator will absorb
approximately 20kW of beam power and will require water cooling,
probably thorough an isolated RAW (radioactive water) loop heat
exchanged with the LCW flow. Shielding of the collimators will require
approximately 1m of radial iron followed by 50cm of radial concrete over
a length along the beam line of \~15m to allow free passage of
rad-trained personnel. This will require locally enlarging the tunnel
cross section but should not require a bypass tunnel.

### 5.3.5 IR Protection {#ir-protection .unnumbered}

A sophisticated system must be designed to protect the IR SC magnets,
particularly from kicker misfires. As in the LHC \[14\], it will consist
of a front collimator, inner and intermediate absorbers in the inner
triplet, and of a neutral beam dump and several collimators in the outer
triplet. The similarity of the Stage 1 IR layout to the LHC makes it
likely that a similar protection layout would be workable. The length of
these sacrificial collimators will need to be increased due to the
increased energy and decreased beam spot size of the VLHC beams.

####  {#section-12 .Reference-heading .unnumbered}

####  {#section-13 .Reference-heading .unnumbered}

####  {#section-14 .Reference-heading .unnumbered}

####  {#section-15 .Reference-heading .unnumbered}

####  {#section-16 .Reference-heading .unnumbered}

####  {#section-17 .Reference-heading .unnumbered}

####  {#section-18 .Reference-heading .unnumbered}

#### 5.3.6 Worst-Case Beam Accidents {#worst-case-beam-accidents .Reference-heading .unnumbered}

Work has begun on understanding the implications of a "worst-case" beam
accident in the VLHC. The assumption is that some unspecified agent
causes the beam to be kicked out of the machine with a rise time fast
compared to the revolution frequency, so that the normal beam abort does
not have time to act. This agent is also assumed to possess a "kicker
flat top" accurate enough (\<1%) that then beam is effectively held in
one place for the duration of the accident. Under these assumptions the
beam will rapidly melt a hole in the magnet and impact the tunnel wall
at near grazing incidence (3-5mrad).

A preliminary observation is that the nearby cryogenic piping would
explode due to the instantaneous temperature rise. This would also be
true of the Tevatron, HERA, and the LHC so it is important to keep this
mysterious agent out of these machines as well. The cryo piping is
contained inside carbon-steel structures (vacuum jackets and magnet
iron) which would limit collateral damage. It would probably not even be
noticed from the outside of the magnet. This is not our biggest problem.

A second observation is that the "beam drilling" scenario (in which a
stable beam vaporizes a small channel deep into the target) is
impossible at grazing incidence, even if the beam were perfectly
extracted on a single trajectory. This beam drilling scenario is
expected when the beam is normally incident onto a semi-infinite slab of
material such as a beam absorber block. However at grazing incidence,
the imbalance of the mechanical forces near the beam impact point (due
to local heating of the rock) will cause a rock chip to "spall" out from
the tunnel wall. This spalling behavior has been observed during rock
excavation tests with electron beams \[15\] and follows this simple
mechanical model. This spalling effectively sweeps the beam and
guarantees that fresh (i.e. non-vaporized) material will be available to
initiate the shower even if the beam is extracted perfectly. Thus the
pattern of energy deposition can be calculated accurately enough by
assuming that the shower initiates at a more-or-less fixed position near
the point of grazing incidence.

A MARS calculation has been performed (Figure 5.59) to evaluate the
energy deposition under the assumption that both the rock and beam
position remain fixed. The simulation indicates that a region 8 meters
long and about 15cm in radius are heated to the melting point of
Dolomite. Obviously the lava will splatter to the floor. The next step
in the calculation (in progress) is to use ANSYS to evaluate the thermal
stresses in the surrounding rock and estimate the amount of rock which
breaks off from thermal stress. The rise time of the heat pulse (
 machine revolution or about 0.8 msec) allow the mechanical stresses to
relieve themselves on the scale of a couple of meters, so a static
mechanical analysis is approximately valid.

![](media/image68.png){width="2.748611111111111in" height="2.7125in"}
![](media/image69.png){width="2.5in" height="2.7131944444444445in"}

Figure 5.59. VLHC Stage 1 beam at 6.5 mrad grazing incidence on tunnel
wall.

A more realistic situation in which the beam angle sweeps by even a few
milliradians during extraction changes the situation significantly. In
this case the heating is distributed into a large enough rock mass that
the only a very small region (of order a centimeter wide) is approaches
the melting point. The picture becomes that of a destroyed magnet, a
centimeter-wide scar on the tunnel wall, and an amount or residual
radiation comparable to that of a 4-hour continuous beam loss at the
Fermilab Main Injector.

#### References *{ed. note---for sec. 5.3}* {#references-ed.-notefor-sec.-5.3 .Reference-heading .unnumbered}

\[1\] Proc. of ICFA Workshop \"Beam Halo and Scraping\", Ed. N.V. Mokhov
and W. Chou, Lake Como, Wisconsin (1999).

\[2\] Bryant & Johnsen, "Circular Accelerators and Storage Rings", p.308

\[3\] A.I. Drozhdin and N.V. Mokhov, "Energy Deposition Issues in the
Very Large Hadron Collider", Workshop on VLHC, Fontana, Wisconsin,
February 22-25, 1999.

\[4\] A.I. Drozhdin , N.V. Mokhov, C.T. Murphy, S. Pruss, "*Beam Abort
For a 50X50 TeV Hadron Collider",*
<http://fnalpubs.fnal.gov/archive/vlhc/VLHCPub-51.ps>

\[5\] Baishev, I.S., Drozhdin, A.I., Mokhov, N.V., Parker, B.,
Richardson, R.D., Zhou, J. *"Dealing with Abort Kicker Prefire in the
Superconducting Super Collider," ,*PAC 93, Washington, DC, May 1993

\[6\] The Large Hadron Collider, Conceptual Design, CERN/AC/95-05(LHC)
October 20, 1995..1.5

\[7\] D.C. Wilson, C.A. Wingate, J.C. Goldstein, R.P. Godwin, N.V.
Mokhov, \"Hydrodynamic Calculations of 20-TeV Beam Interactions with the
SSC BEAM Dump\", Proc. of IEEE Particle Accelerator Conference, p. 3090.
(1993). A legendary SSC video contains a visualization of the extracted
SSC beam drilling a hole in the absorber block when the sweeping magnet
system fails. We should put this online.

\[8\] N. Mokhov, pvt. comm.

\[9\] R. Yarema, pvt. comm.

\[10\] LHC Talk at Beam Instrumentation Workshop '00

\[11\] S. Hunt, S. Crivello, N. Mokhov, \"Radiation Effects on Optical
Fiber Links at the SSC\", Nucl. Instr. Meth in Phys. Research, A352
(1994) 329-243.

\[12\] A.I. Drozhdin and N.V. Mokhov, "*The VLHC Beam Collimation
System*," VLHC design study note.

\[13\] A.I. Drozhdin, N.V. Mokhov and A.A. Sery, "The Very Large Hadron
Collider Beam Collimation System", Workshop on VLHC, Fontana, Wisconsin,
February 22-25, 1999.

\[14\] N.V. Mokhov and J.B. Strait, \"Towards the Optimal LHC
Interaction Region: Beam-induced Energy Deposition\", Proc. of IEEE
Particle Accelerator Conference, p. 124 (1997).

\[15\] Electron Beam Tunnel Boring papers from LBL circa 1975

### 5.3.7 General ES&H Considerations {#general-esh-considerations .unnumbered}

*{ed. note: this section will be derived from the following material
provided by Don Cossairt}*

**Potential Environmental, Safety, and Health Issues**

**Environment, Safety, and Health Considerations for a New Accelerator
Facility**

**I. Introduction**

All of the possible future accelerators under study present a number of
considerations in the general area of environment, safety, and health.
It is the intent of this chapter to identify the character of these
challenges in a general way. The environment, safety, and health issues
peculiar to a particular possible accelerator are discussed in the
chapters related to that technology. Some of the considerations which
much be taken into account are very similar to those that have been
encountered and solved during the construction and operation of other
facilities at Fermilab and at similar laboratories elsewhere in the
United States and worldwide. Other considerations have not been
encountered on the same scale previously in connection with the
construction and operation of accelerator laboratories. These novel
issues will require particular attention as such a project proceeds to
assure their timely resolution in a manner that is cost-effective and
that meets the approval of the public. In this chapter, both the
conventional and the novel issues are discussed, with perhaps more
emphasis devoted to the latter. It is concluded here that with adequate
planning in the conceptual design stages, these problems can be
adequately addressed in a manner that merits the support of the
Laboratory, the Department of Energy, and the public.

**II. Procedural/Regulatory Matters**

The actual design, construction, and operation of any future accelerator
will have to meet a number of procedural/regulatory milestones in the
area of environment, safety, and health to assure timely and continued
support of this project by the public and by the Department of Energy.
The devotion of early attention to these issues is likely the best way
to enhance public support of any chosen accelerator technology.
Requirements in environment, safety and health are currently set forth
as a part of Fermilab\'s Work Smart Standards in Environment, Safety,
and Health that are incorporated in the current version of the contract
between Universities Research Association and DOE. Currently, the Work
Smart Standards are reviewed annually to assure that they adequately
address the hazards of the laboratory, including those of any new
facility. If changes are necessary they are negotiated with the DOE-FRMI
Group and the URA-DOE contract is revised accordingly. These standards
include listings of applicable Federal and State Regulations as well as
internally developed policies and national standards (WSS 99). Of
course, the contract under which Fermilab or a future accelerator might
operate in the future is likely to change in ways that could modify the
applicable requirements.

**A. [Environmental Protection Procedural/Regulatory
Matters]{.underline}**

All DOE activities are subject to the requirements of DOE\'s regulations
for implementing the National Environmental Policy Act (NEPA) (CFR 97).
First, any new project of the magnitude of those under consideration in
this report will be the subject of an Environmental Assessment (EA). A
review will be done of all possible impacts of this project on the
environment and the public. The required analysis is broad in scope and
includes societal impacts along with those topics that are more
generally associated with environmental protection such as the
discharges of pollutants, effects upon wetlands and floodplains, and
exposures of people to chemicals and radioactive materials. It will
include a review of the alternatives of carrying out the project
elsewhere or not at all. This process is centered on the production of a
comprehensive document but also includes the participation of the public
by methods that will be chosen by DOE. As a result of the environmental
assessment process DOE will either issue a Finding of No Significant
Impact (FONSI) or conclude that that the preparation of an Environmental
Impact Statement (EIS) is necessary. An EIS may well be required due to
the size, scope, cost, or impact on the human environment of the
project. For example, it is likely that an EIS will be required for any
new facility that extends beyond the present boundary of the Fermilab
site. The completion of the EIS process results in the issue of a formal
public notice called a Record of Decision (ROD). The EIS process is
generally considered to be an arduous one, but one that can be followed
to a successful conclusion stated in the ROD. The preparation of an EIS
is certain to be a large task having significant cost, customarily
accomplished using external resources. Regardless of the eventual path
of the NEPA process, project funds cannot be issued to support such a
Congressional \"line item\" project beyond the early conceptual stage
prior to the successful completion of the NEPA process. It is thus
crucial that this process be conducted in a manner that is honest and
which comprehensively addresses the potential concerns of members of the
public. A good working relationship with the Department of Energy is
also a necessity to a successful result.

Other procedural requirements apply in the area of environmental
protection. These will be more certainly identified as a part of the
NEPA process but early planning may well serve to avert problems later.
DOE facilities are generally subject to Federal and State environmental
protection regulations promulgated chiefly by the U. S. Environmental
Protection Agency (USEPA) and the Illinois Environmental Protection
Agency (IEPA), respectively. There are environmental permits to obtain
from both state and federal authorities that are likely to be found to
apply to any of the possible facilities. Some of these apply during the
construction stages, others apply during operations, and some apply
during both stages. Permits are likely to be required to cover such
topics as storm water discharges, discharges of cooling water, wetlands
mitigation, releases of air pollutants for both non-radioactive
pollutants and for radionuclides, and construction in any floodplains.
Archaeological sites are also located in the region that might need
further investigation and study prior to the commencement of
construction. The preparation of the applications for these permits and
approvals is generally straightforward, but must be accomplished with
the long lead times, typically 180 days, required by the issuing
agencies. Early coordination with the project design team should greatly
facilitate completion of the associated milestones. Any chose
accelerator is likely to be initially viewed by the public and by
Federal and State regulators as a poorly understood, esoteric
technology. In recognition this and also of the fact that any of the
chosen accelerators will involve some sort of impact beyond the
geographical boundaries of the present Fermilab site, early coordination
with the Federal and State regulatory agencies is recommended as a
vehicle to promote enhanced understanding of the nature and impact of
the chosen facility.

**B. [Safety and Health Procedural/Regulatory Matters]{.underline}**

In accordance with the Fermilab\'s Work Smart Standards, the Laboratory
will be required to prepare an assessment of the environment, safety,
and health issues associated with this project in the form of a Safety
Assessment Document (SAD). Given the size, scope, cost, and novelty of
any of the candidate facilities, the preparation of a first stage
document called a Preliminary Safety Assessment Document (PSAD) is
needed. The purpose of the PSAD is to identify the relevant
environmental, safety, and health issues at an early stage and propose
how they might be mitigated. A final Safety Assessment Document (SAD),
then, documents the resolution of all the pertinent issues raised by the
PSAD. Environmental issues are customarily integrated into the PSAD/SAD
process to promote program cohesiveness. Given the scope of any of the
candidate projects discussed elsewhere in this report, it is nearly
certain that DOE will choose to review these safety documents by
utilizing an external review team composed of both DOE staff and
representatives from other DOE facilities. Just prior to facility
operation, a readiness review will be conducted in similar fashion using
an external review team. DOE has specified a somewhat more rigorous
procedure for the conduct of this safety review process in its Orders.
The details of the procedures to be followed in the safety review
process will be determined by the terms of the contract under which the
Laboratory is operated at the time the project might proceed. Unlike
NEPA assessment activities, PSAD/SAD activities generally begin after
funds are issued. Nevertheless, careful consideration of PSAD/SAD in the
design can only result in beneficial results. Efforts should be taken at
early stages to promote consistency between the conclusions of the NEPA
assessment and the safety and health documentation.

DOE is presently \"self-regulating\" in the areas of industrial safety
and occupational radiation protection. There is a possibility that
during the development of the next accelerator facility, DOE activities
might become subject to \"external\" regulation in these areas, as well
as in occupational radiation protection. It is difficult at this time to
anticipate the form such external regulation might take or which
agencies might be involved. Fermilab staff and DOE continue to monitor
the status of DOE self-regulation in order to identify new requirements
or procedures that might apply to Laboratory activities.

**III. Occupational Safety During Construction**

Any of the accelerators under consideration will involve a great deal of
construction. In regions where the standard \"cut and fill\" method used
elsewhere successfully at Fermilab for many years, the standard
practices embodied in the Occupational Safety and Health
Administration\'s (OSHA\'s) regulations on the safety of construction
activities will be followed (see WSS 99). Particular requirements that
address excavations, the provision of applicable personnel protective
equipment, coordination of emergency response measures, fire safety,
chemical safety, and electrical safety would apply as they have for many
years to other civil construction projects on the Fermilab site.
Adequate means of egress of construction workers would need to be
provided. Given the nature of the candidate facilities, somewhat unlike
present facilities, significant slopes may be involved in some
locations. Well-thought means of prevent of accidents due to heavy
objects moving downhill should be included in the design.

The candidate facilities all involve a considerable amount of tunneling
in bedrock units, some of it horizontal and others with slopes. In
addition to the safety requirements pertaining to construction
activities, Federal regulations pertaining to underground operations
(e.g., \"mining\" activities) come into play. Solutions to these issues
are being developed to address challenges of this type encountered in
the excavation for the NuMI project. These include the standard concerns
about tunneling safety and material movement as the tunneling proceeds.
The choice of construction methods between the use of Tunnel Boring
Machines (TBMs) or the employment of drilling and blasting methods will
most likely be one of economics or availability. However, either
alternative has associated occupational safety considerations.
Provisions for emergency response including underground rescues will be
needed. Again, egress issues relevant to protection of the construction
workers will be of paramount importance.

Given the location within several major aquifers, and the existence for
some facilities of downward slopes at certain locations, it is clear
that stringent measures must be taken to prevent flooding both during
the construction period and thereafter. This problem must be addressed
in harmony with the related environmental protection concerns (see
Section IV). Likewise, any downward slopes in the bedrock units will
require the same attention to the prevention of uncontrolled movements
of heavy objects downhill as in the \"cut and fill\" zone. While such
control measures are well within those encountered in mining operations
elsewhere, they are novel at accelerator laboratories. The existence of
any steep slopes also needs to be carefully considered in planning for
emergency rescue operations that conceivably could be needed during
construction.

During project construction, industrial radiography, a tool commonly
used in general industry, is likely to be employed to assure the quality
if pipe welds, etc. Such radiographic operations, which typically use
radioactive sources of high activity and relatively hazardous compared
with the sources commonly used in particle physics experiments, would
need to be conducted in compliance with the pertinent requirements of
the State of Illinois in order to control the hazard to personnel of
these intense radioactive sources. In the course of construction, other
radiation-generating devices such as soil density gauges and media
water-content probes might also need to be used. Standard procedures
pertaining to such activities should be applied.

**IV. Environmental Protection During the Construction**

All of the candidate facilities will be placed in whole or in part
underground. Some portions will be located near the surface, in the
glacial till, while others will be located underground in the various
rock strata. For the portions near the surface, construction may proceed
by cut and fill techniques similar to those employed to build most of
the present facilities at Fermilab. Erosion control measures similar to
those in practice for a number of years will be employed in accordance
with good engineering practice and Federal and State regulations. Dust
from any spoil piles must be kept under control. Likewise, a storm water
management plan will need to be developed. If 5 acres (2.0 hectares) or
more of land surface are impacted by the construction, a National
Pollutant Discharge Elimination System (NPDES) Stormwater Permit for
construction will be needed which will include specific actions which
must be followed during the construction period. The usual precautions
to prevent pollution from spills of regulated chemicals from the
construction equipment will need to be taken. Noise from construction
activities is not expected to be significantly larger than that
associated with normal civil construction activities in the vicinity of
Fermilab.

The NEPA process described in Section II.A should result in a
determination of the impact of the project on wetlands and or
floodplains. A general description of how any identified effects will be
mitigated will have been developed. For example, if more than 3 acres of
wetlands are identified, it may be necessary for compensatory man-made
wetlands to be created. Rearrangement/enlargement of the Fermilab pond
system might prove to be necessary to compensate for possible
interference with floodplains. It may be especially important to
demonstrate adequate care for floodplains due to significant local
public concerns about flood prevention.

Tunneling in the bedrock units will result in the removal of a
considerable volume of rock, dependent upon project details. The
management of the spoil is a major issue that must be addressed and
provisions for its proper stockpiling provided. In particular, concerns
about dust may be more severe for this material, largely pulverized
rock. The duration of this storage may be temporary for the spoil that
is of marketable quality and longer for that requires reuse at Fermilab
or disposal. This should be carefully planned in accordance with
Fermilab\'s longstanding tradition of placing high importance on
aesthetic issues. The management of spoil materials will need especially
vigorous attention if its removal at any off site locations is needed.
The placement of such a project in any aquifers results in the need to
protect drinking water resources from contamination during construction.
Also, the \"dewatering\" of tunnels as the construction proceeds will
require measure to be developed to prevent the depletion of wells and
also to manage effectively any additional water discharges from this
source.

The storm water management plan will need to take into account any
releases of groundwater generated in the course of \"dewatering\" the
tunnel. Careful hydrogeologic studies need to be performed to understand
the interplay of the construction of the project with the various
aquifers. This must be done to establish with certainty that the
construction activities will not cause significant perturbations of the
local individual and municipal water supplies, either in quality or in
quantity. It should be mentioned that the exact depth of the various
aquifers are not known in detail at all locations involved in the
proposals discussed in this report. Accurate measurements will be
needed, through geological investigations over the entirety of the
affected region. The results can be used to plan a strategy for
preventing the tunnel from serving as a possible path of
cross-contamination from one aquifer to another. During construction
activities, precautions are needed to guarantee that spills of
chemicals, including lubricants and fuels from the construction
equipment, are captured before they enter the groundwater. The presence
of any downward slopes presents special considerations in this regard
that should be addressed.

Tunneling activities can generate considerable noise and vibration.
Should blasting techniques be used, quantitative standards apply to the
amplitude of the vibrations that are allowable at the surface. Noise
exposure, both occupational and to the public at the site boundary and
at off site locations will be an issue that needs to be addressed.

**V. Occupational Safety During the Operations**

**A. [\"Ordinary\" Occupational Safety Hazards]{.underline}**

The occupational safety hazards encountered at all other large particle
accelerator facilities will be found in all of the candidate facilities.
In this section, the focus is on the issues that have been successfully
addressed before, at Fermilab and elsewhere. These have been
successfully addressed by well-known techniques and are simply listed
here, along with the corresponding safety and health needs, for
completeness:

-   The facility will use high current electrical circuits on a large
    scale. Present techniques in managing power distribution and
    providing means to effectively lock out supplies should be adequate
    to address the electrical hazard.

-   Radiofrequency (RF) generation and distribution equipment will be
    used extensively. Present techniques for controlling possible
    exposures to non-ionizing radiation should be sufficient.

-   Large amounts of cables in cable trays will be installed. Current
    methods for addressing fire protection concerns should be adequate.

-   Long tunnels will be present. There is a need to adequately address
    Life Safety Code/fire protection issues to assure adequate
    provisions for egress and adequate means of prevention of and
    response to fires.

-   There will be movements and alignment of large, heavy components.
    There is a need to include considerations in the design related to
    ease of movement of equipment to facilitate the prevention of
    injuries.

All of these issues can be readily addressed by applying the present
collective experience to the design at an early stage.

**B. [Novel Occupational Safety Hazards]{.underline}**

This section is directed to those occupational safety hazards that are
not generally encountered at accelerator facilities. These will all
require consideration in the early planning stages in order to be
addressed in an efficient manner.

*i. Large Scale Use of Cryogens*

This facility requires the extensive use of superconducting materials
and cryogenics in both magnets and RF structures. While these
technologies are relatively new, a number of accelerators world-wide
have developed techniques adequate for addressing them. Provisions will
need to be made for the safe release of cryogens to the surface both
during normal operations and in the event of quenches. Current
accelerator facilities have developed mechanisms for using skilled
engineers to independently review such systems for safety during the
design and commissioning stages. The result has been the development of
a number of standard engineering practices to mitigate both direct
cryogenic hazards and the accompanying oxygen deficiency hazards (ODH).
This general approach, if taken, should adequately address these.

*ii. Ionization Cooling Technology*

Some concepts involve the use ionization cooling, a choice that presents
some novel hazards. The use of liquid hydrogen (LH~2~) is being
considered as a possibility preferable to hazardous or toxic materials.
While this choice may be preferred from environmental protection and
industrial hygiene standpoints due to the lack of the potential for
spills or exposures to hazardous or toxic materials, the fire/explosion
hazard represents an important consideration. In an ionization cooling
system, the LH~2~ cells will be interleaved with RF structures and
magnets that apply a great deal of electrical energy. The impact of the
absorption of energy from the particle beams is also a consideration. In
view of these considerations, a recommended approach would be to convene
a review committee of qualified individuals at the earliest reasonable
state in the design of any facility chosen which incorporates this
technology to assure adequate, cost-effective solutions.

*iii. Life Safety-Egress Considerations*

As during construction, the strong desire to minimize the number of exit
points will render adequate design and engineering with respect to the
Life Safety Code imperative. It is likely that special means of
communication underground will need to be provided, \"refuge\" locations
incorporated into the design, and adequate means of transport of
personnel, both healthy and injured, to the surface established. These
provisions will need to incorporate recommendations of a qualified fire
protection professional at the time of the development of the conceptual
design in order to assure adequate allowances for their costs. Later
involvement of fire protection engineering will also be needed as the
detailed design proceeds.

**VI. Ionizing Radiation Safety During Operations**

**A. [Prompt Radiation Shielding]{.underline}**

All of the possible choices of the future accelerator will likely
require significant amounts of passive shielding to attenuate prompt
radiation to levels acceptable to the members of the public. Indeed,
this fact is implicitly recognized by the proposed siting of these
facilities deep underground. The shielding demands of proton
accelerators are generally recognized to greatly exceed those of
electron machines especially with regard to attenuating the neutrons
produced at large angles. At the forward angles, given the copious
production of muons, and the increased importance of range-energy
straggling at high energies (Va87), the shielding requirements of any of
the new machines increase rapidly with energy and must be
well-understand at the earliest possible stage in the design and in the
NEPA process.

Some detailed understanding of the pertinent requirements must preface
further discussion. Current Department of Energy requirements are not
well-matched to discussions of radiation fields that exist beyond the
boundaries of DOE sites. DOE has specified the annual limits on the
radiation dose equivalent that can be received by occupational workers
and members of the public (see Regulation 10 CFR 835 in WSS 99 and DOE
93). These limits, in all situations expressed to date, pertain to the
dose equivalent delivered to people or to locations where people could
reasonably be. For individual members of the public, the primary limit
is 100 mrem (1 mSv) in a year, not including man-made, medical, or
enhanced natural radioactivity. This limit is intended to apply to all
sources of radiation exposure that a person might receive, even from
non-DOE manmade sources. Special reporting requirements apply when the
annual dose equivalent received by an individual exceeds 10 mrem (0.1
mSv) in a year. DOE has expressed the view that nonoccupational annual
doses to real members of the public are not expected to exceed a few
mrem in a year. In light of public concerns about radiation exposures,
any new facility should be designed to keep the dose that could be
reasonably received by actual members of the public to as small a value
as possible. Higher annual dose equivalents at underground locations
inaccessible to people but beyond the control of host laboratory might
well be allowable. These criteria should be selected early in the NEPA
process with the support of DOE secured. As a convenient reference
point, the average annual radiation dose equivalent received by
individuals living in the United States is about 360 mrem (3600
microSv). Of this exposure, about 300 mrem (3000 microSv) is due to
natural sources, including exposure to radon indoors (NCRP 87).

While the proper shielding against hadrons (mostly neutrons) and
electrons at high energy accelerators is quite well understood, several
new problems must be successfully solved for most of the facilities
under consideration. The likely large dimensions of the facility coupled
with the long ionization ranges and the increased importance of the
range-straggling phenomenon of muons in any new regime of higher energy
will require that the curvature and profile of the earth\'s surface be
taken into account to assure valid shielding calculations. Also, for
some facilities prompt radiation dose due to neutrinos may arise as a
significant consideration for the first time (Mo 99). Both of these
problems have considerable impact upon the selection of the
\"footprint\" of controlled, and uncontrolled property that is needed
for or impacted by the facility.

**B. [Residual Radioactivity of Components]{.underline}**

Several of the accelerators under study will have portions that must
handle beam powers of unprecedented magnitude. As is well known, in the
high energy region, most, but not all, of the radiation effects scale
roughly with the beam power for either accelerated electrons or protons.
In particular the effects of high residual activity levels should be
carefully taken into count at early stages of design of collimation
systems, targets, ionization cooling apparatus and other locations of
possible high losses of beam. The usage of materials in the target
stations of high atomic number and which might not be solids at their
operational temperature merit significant, early attention as plans
proceed and choices are made. Doses that might be received by workers
are an important subject that must be assessed as a part of the NEPA
process. The need to minimize the generation of radioactive wastes and
to eliminate the creation of wastes that contain materials that are both
toxic or hazardous and which contain radioactive is an important concern
at all points during the design effort.

**C. [Airborne Radioactivity]{.underline}**

The production of airborne radioactivity at a future accelerator needs
careful consideration. Federal Regulations promulgated by the U. S.
Environmental Protection Agency (EPA) have established an annual limit
on dose equivalent of 10 mrem (100 microSv) to any member of the public
that can be received as a result of operations of DOE facilities such as
accelerators (CFR 89). Further, the same regulations impose stringent
continuous monitoring requirements if the annual dose equivalent to any
member of the public is to exceed 0.1 mrem (1 microSv) in one year. In
addition, if the level of 0.1 mrem in one year is to be exceeded, then
an application for approval to construct and a notification of startup
must both, in proper sequence, be submitted to the U. S. Environmental
Protection Agency. Given the nature of the proposed facilities and their
extent beyond the present boundaries of the Fermilab site, careful
attention must be paid to the production of airborne radioactivity. The
high beam power of any of the possible machines can lead to the
production of airborne radionuclides that, while generally of short
half-life, have the potential to deliver annual doses above allowable
levels in areas accessible to the public. Care in design should be able
to mitigate these releases.

**D. [Radioactivity in Soil and Groundwater]{.underline}**

The placement of any of the future facilities in both the glacial till
and the underlying bedrock requires that the production of radioactivity
in these hydrogeologic units be given careful attention. Again the
anticipated beam powers require careful consideration of such
radioactivity. Before the exact footprint of any chosen facility is
irrevocably determined, detailed hydrogeologic studies should be
conducted to determine the relevant parameters precisely, as they are
known to vary significant in the vicinity of the Fermilab site. It is
clear that protection of groundwater against contamination with
radioactivity merits early, detailed attention in project design to
assure satisfaction of likely public concerns. It may well be that the
most prudent choice of design objectives might be far below present
regulatory standards for drinking water.

**VII. Non-Radiological Environmental Protection Issues During
Operations**

Operations of the facility should be planned in a way that incorporates
proper measures to control the generation of non-radioactive wastes.
Further, there is a need to address potential spills of hazardous or
toxic materials in a way that fully protects members of the public and
of environmental resources. The detailed attention to these issues will
be required as part of the NEPA process and the designs should provide
information of the quality needed to support all required permit
applications to State and Federal environmental regulatory agencies. For
the operational facility, in any enclosures located deep underground the
cross-contamination of the various aquifers must be prevented and any
dewatering operations must assure that local community or individual
drinking water supplies are not perturbed.

**VIII. Summary**

All of the candidate facilities result in a number of challenges in the
area of environment, safety, and health. Many of these have been
encountered, and effectively addressed, at other accelerator facilities.
Some of the problems are common to other recent projects undertaken at
Fermilab and elsewhere that have resulted in the need to develop new
methods to address them. Given the new scale of any of the candidates,
and their nature, some of these issues may have a greater importance
than found in the present experience. It is concluded here that with
adequate planning in the design stages, these problems can be adequately
addressed in a manner that merits the support of the Laboratory, the
Department of Energy, and the public.

**References**

CFR 89 United States Code of Federal Regulations, Title 40, Part 61,
Subpart H, \"National Emissions Standard for Hazardous Air Pollutants
(NESHAP) for the Emission of Radionuclides other than Radon from
Department of Energy Facilities\", 1989.

CFR 97 United States Code of Federal Regulations, Title 10, Part 1021,
\"\[Department of Energy} National Environmental Policy Act
Implementation Procedures\", 1997.

DOE 93 U. S. Department of Energy, \"Radiation Protection of the Public
and the Environment\", DOE Order 5400.5, January 7, 1993.

Mo 99 N. V. Mokhov and A. Van Ginneken, \"Neutrino Induced Radiation at
Muon Colliders\", presented at the 1999 Particle Accelerator Conference,
New York, New York, Marcy 19-April 2, 1999, FERMILAB-Conf-99/067.

NCRP 87 National Council on Radiation Protection and Measurements,
*Ionizing radiation Exposure of the Population of the United State and
Canada from Natural Background Radiation,* NCRP Report No. 94, December
1987.

Va 87 A. Van Ginneken, P. Yurista, and C. Yamaguchi, \"Shielding
calculations for multi-TeV hadron colliders\", Fermilab Report FN-447
(1987).

WSS 99 \"Fermilab Work Smart Standards Set\", Fermi National Accelerator
Laboratory, http://www-lib.fnal.gov/library/protect/worksmart.html,
November 15, 1999.

[^1]: One unit of harmonic corresponds to 10^-4^ of the main field,
    measured at a reference radius (in our case) of 1cm.

[^2]: Calibration in both a dipole and quadrupole magnet are required
    due to the large gradient which we want to measure with high
    accuracy.