# . Stage-1 Components

## 5.1 Magnets {#magnets .unnumbered}

### 5.1.1 Introduction {#introduction .unnumbered}

The magnet system of the 20 TeV Stage-1 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
\[[^1],[^2],[^3]\] 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 Error:
Reference source not found. 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%/cm 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="6.506944444444445in"
height="4.132638888888889in"}

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 at a 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 Error:
Reference source not found. 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 to
accommodate alignment errors, ground motion, and iron saturation effects
at full field (section 3.2).

![](media/image2.wmf){width="6.601388888888889in"
height="2.857638888888889in"}

Figure 5.2. Correction coils placed at each half-cell boundary (135-m
spacing). The transmission line is diverted down near the current return
bus to provide a field-free region for the correctors.

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 various lengths. The low-beta triplets utilize superconducting
300 T/m cos2 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.

Error: Reference source not found 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  | 67.75 | 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           |       | 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 17 m length 100 kA superconducting test stand \[[^4]\]. This design
study is based on 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 100 kA power supply and current leads (Error: Reference
source not found) are being built for extended system tests. A 50 m
Invar pipe was thermally cycled 1000 times to verify cryogenic weld
reliability in the "zero-contraction" mode \[[^5]\]. 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 \[[^6]\]
and results were in adequate agreement with observations in the 17 m
test loop. The magnetic and mechanical design was refined and several
configurations tested using a room temperature magnetic test stand
\[[^7]\]. 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 \[Error:
Reference source not found,Error: Reference source not found,Error:
Reference source not found,-Error: Reference source not found,Error:
Reference source not found-,[^8],[^9]\] 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.

Error: Reference source not found 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, are described in section 5.1.2.4.

Table 5.2. Main Parameters of Dipole Magnets.

  ----------------- ------------ ---------------------- -------------------
                                 *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

  Sagitta in Magnet              1.6 cm                 0.6 cm

  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      10 mm                  

  Transmission Line              100 kA                 
  Design Current                                        

  Current at 20 TeV              87.5 kA                

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

  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)        
  ----------------- ------------ ---------------------- -------------------

Error: Reference source not found 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 12 m long are shipped to Fermilab from outside vendors. Final
assembly into 65 m 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. The vacuum
system is installed after magnetic measurements are complete. Not shown
are the vacuum antechambers of Error: Reference source not found.

#### 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 1 mm.
The magnet must maintain a high quality field over a 20:1 dynamic range.

![](media/image4.wmf){width="3.7222222222222223in"
height="2.3402777777777777in"}

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

##### 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 1 mm 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 \[[^11]11\]. It is unlikely that these measures 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 Error:
Reference source not found inset). At the highest fields where the holes
are insufficient, quadrupole and sextupole corrector magnets in each
half-cell are needed to regulate tune and chromaticity. No significant
loss of dynamic aperture results from this as discussed in section
3.2.2.3.

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 Error: Reference
source not found). Thus the chosen corrector strengths seem to be
roughly optimized.

Saturation control 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
Error: Reference source not found. 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 150 m 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.

Error: Reference source not found shows the measured effects of putting
the correction holes in the pole laminations on the saturation sextupole
defect 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. Error: Reference source not found 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 0.1 T - 1.85 T and both are about
-8 units at 1.95 T. The beam size at 1.8 T is = 0.2 mm.

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

Figure 5.5. Measured effect of "Holes in the Poles" on the saturation
sextupole defect 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 midpoint 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 Error: Reference source not found.

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 that 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  {#superconducting-transmission-line .unnumbered}

The transmission line is a cylindrical superconducting braid inside a
pipe cooled by supercritical 4.5-6.0 K helium, placed inside a co-axial
cryostat, which in turn is placed at the center of the room temperature
iron yoke. The transmission line (Error: Reference source not found)
consists of (from inside out) a 2.5 cm helium flow space, a perforated
Invar tube, a copper stabilizer braid, the braided superconductor cable,
an Invar pipe to contain the helium, the cold pipe support, a
cryoshield, the superinsulation blanket, and the vacuum jacket. The cold
pipe support centers the conductor cable in 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.png){width="6.204166666666667in"
height="4.029166666666667in"}

Figure 5.7. Transmission Line Drive Conductor.

The main design requirements for the transmission line are as follows.
First, it must contain enough superconductor to carry the specified
current of 100 kA at 6.5 K. This includes a significant margin since the
peak temperature of the cryogenic system is specified at 6.0 K (section
5.2.1) and the required current for 20 TeV is 87.5 kA. It must maintain
a 2.5 cm clear bore for the helium flow in a 10 km 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 0.5 mm 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 Design {#conductor-design .unnumbered}

Three distinct conductor designs are utilized (see Error: Reference
source not found). 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 Error: Reference source not found).

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             |
| > in strand     |             |                 |                   |
+-----------------+-------------+-----------------+-------------------+
| > 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 that 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 Stage 1 it is planned to use a more cost
effective wire optimized for the lower fields and without the constraint
of small filament size. There is also a copper braid placed inside the
superconductor to provide 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. No training or
degradation has been observed during the few quenches per sample tested.

The bus in the 3.5 m long corrector magnet region uses a spiral wrap of
nine 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 in the
superconductor assembly for pressure relief ports 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 braided and spiral-wrapped conductors (and the 10 cm long splice
between them) have been successfully tested in the 100 kA test facility.
power dissipation was \<0.2 W per splice at 100 kA.

The critical temperature vs. current for the braided conductor is shown
in Error: Reference source not found. 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. This slope has been measured on
various transmission line samples and agrees with predictions derived
from short sample parameters. 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 6.0 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/image8.wmf){width="5.129861111111111in"
height="3.2430555555555554in"}

Figure 5.8. The critical temperature vs. current for main drive and
return conductors. The design has a temperature margin of 0.7 K at
90 kA, or a current margin of 20 kA at nominal temperature.

Detailed thermohydraulic simulations \[8\] have 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 its 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.

The quench propagation velocities were measured in a 17 m long conductor
loop \[4\]. Although the properties of the conductor in the 17 m loop
are not identical to the final design, the general behavior should be
similar. 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 at \~80 kA. Above this current, it rises
exponentially reaching about (30-40) m/s at 100 kA. This indicates that
by applying a current dump circuit of a time constant of 1 second, the
quench zone would be at most half the length of a dipole magnet (34 m).
Repeating these tests with long lengths of the final transmission line
is an important goal of the R&D program.

*Cryostat Design*

A cross-section of the drive conductor cryostat is shown in Error:
Reference source not found. The support spider consists of an 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 on 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 5.9. 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.

#### 5.1.2.3 Mechanical and Thermal Design of Transmission Line Magnet {#mechanical-and-thermal-design-of-transmission-line-magnet .unnumbered}

##### 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 at two points and transported
using a lifting fixture (load spreader bar) which weighs 1/3 as much as
the magnet and is small enough (2 m 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. Cryogenic heat
load from transmission line splices is about 0.4 W per magnet end or
\<10% of the total 5 K heat load. Labor estimated for tunnel splicing is
\~60 person-hours per magnet end which corresponds to \<\$10 M 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 as 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 5 mm 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.

The magnet is installed on vertical support/adjusters every 6 m. This
distance was chosen \[[^12]\] 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 maximum stress does not exceed 50 -- 60
MPa.

###### Force Needed to Introduce Alignment Bumps {#force-needed-to-introduce-alignment-bumps .unnumbered}

The force needed to introduce the 1.6 cm global sagitta into the 67-m
magnet assembly is very small (\<10 kg). However large forces may be
generated on individual support/adjusters if they are driven in opposing
directions during magnet alignment in the tunnel. To estimate forces and
deformations of the straight magnet structure during alignment, 3D
numerical simulations were performing using a 12-m section model
\[[^13]\]. Forces were applied on a single support/adjuster connected to
the vacuum tube at the center of the model, and the model ends were
restricted from motion or rotation. The model also had a distributed
weight load from the laminations in addition to the horizontal force
applied by the adjuster. The force needed for 1 mm motion is 450 kg. The
result shows the magnet twists slightly because the force is not applied
along the neutral axis of the magnet assembly. The block moves about 0.9
mm for a 1 mm movement of the vacuum tube. The difference in relative
movement of the iron halves of the magnet can reach 30 m.

###### Yoke Deflection and Gap Stability under Magnetic Forces {#yoke-deflection-and-gap-stability-under-magnetic-forces .unnumbered}

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 \~20m. Several
prototypes were built before identifying a viable and economical design.

The laminated magnet yoke (Error: Reference source not found) 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 (Error: Reference source not found) aside from that expected
from iron saturation \[[^14]\]. 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}

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 \[[^15]\]. At a current of 100 kA, 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. The vertical force
gradient gives rise to an instability \[[^16]\] 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.

Spiders made of ULTEM \[[^17]\] centrally position the conductor. Pegs
are nominally 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 combined tolerance
stackup of the cryopipe diameter, spider leg lengths, vacuum jacket wall
thickness, and lamination geometry. See section 5.1.6.3. The pressure
range is 20-40 kg. These numbers increase up to 70-100 kg in cold
conditions and under the action of magnetic forces.

Prototype injection-molded supports were exposed to 100,000 mechanical
cycles with a load force of 300 kg/m (three times that expected)
\[[^18]\]. 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 \[[^19]\]. The sliding behavior needs
to be carefully verified in system tests. If it is insufficient, other
rolling or sliding support systems can be used \[[^20],[^21],[^22]\].

###### Magnetic Forces on the Current Return Conductor  {#magnetic-forces-on-the-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 (see
Error: Reference source not found) 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 that can not be allowed to contract as the
pipes cool down. Most materials will be damaged if they are cooled down
to cryogenic temperatures but not allowed to contract (Error: Reference
source not found). Expansion bellows can be used for normal cryogenic
piping but not with the transmission line conductor. The best solution
for the conductor is to use materials such as Invar that will go into
tension but will 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 5 K
with ends constrained

+----------------+------+-------+--------+---------+-------+--------+
| ##### Mate     | *    | *E(   | *=     | *yield* | *yi   | *      |
| rial {#materia | dt,* | 5 K)* | E\*dt* |         | eld/* | L(mm)* |
| l .unnumbered} |      |       |        | *MPa*   |       |        |
|                | *m   | *GPa* | *MPa*  |         |       | *L=    |
|                | m/m* |       |        |         |       | 135 m* |
+----------------+------+-------+--------+---------+-------+--------+
| > 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 in our conductor
(independent of length) 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
\[[^23]\] as part of the VLHC R&D program. A 50 m Invar tube containing
128 automatic girth welds was thermally cycled 1000 times from 300 K to
77 K with the ends constrained. No leaks were detected at a sensitivity
of 10^-10^ std cc/sec.

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

The magnet anchor system consists of the vacuum barriers, the
force-anchors, the transportation locks and the vacuum jacket anchors,
as shown in Error: Reference source not found.

![](media/image10.wmf){width="5.986805555555556in"
height="2.308333333333333in"}

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

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 135 m). Two 67‑m magnets will be hard-welded
together into a single 135‑m assembly. The vacuum jacket is also
connected to the ground every 135 m at the anchor point. 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
\[[^24]\]. There will be expansion joints in the vacuum jacket and beam
pipes on one side of this anchor. Magnet adjusters will permit 2-3 cm of
longitudinal motion for normal tunnel temperature variations.

Cryogenic piping will be anchored at the 135 m 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 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 an internal tube liner and an outer protecting skin.

Vacuum barriers and quench pressure reliefs occur at the anchor location
in every 8^th^ magnet (540 m). The vacuum breaks are used to insulate
subsystems in order to facilitate installation, troubleshooting, and
repair. They provide a good vacuum in the transmission line ring section
\[[^25],[^26]\]. The vacuum barriers are designed to withstand a
differential pressure of 0.15 MPa and to minimize the heat in-leak
\[[^27]\]. 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 longitudinal 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 graphite fiber composite
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 Error: Reference
source not found.

![](media/image11.wmf){width="6.572916666666667in"
height="2.8381944444444445in"}

Figure 5.11. Magnet interconnections with bellows and correctors at the
half-cell boundaries (left), and the hard-welded connection at the
quarter-cell boundary (right).

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 take place directly over the
copper/superconductor structure without damaging it. A picture of the
splicing operation is shown in Error: Reference source not found.

Three cryo-service pipes having bellows will be orbital welded
automatically. An aluminum thermal shield made from two pieces will
cover all the pipeline connections \[[^28]\]. 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.

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

In Stage-1 there are independently powered dipole, quadrupole and
sextupole correctors in the 3.5 m free space at the boundary of each
135 m half-cell. See Error: Reference source not found. 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
3-mm "3-bump" in the closed orbit at full energy. Quadrupole correctors
have sufficient strength to overcome the gradient shift from magnet
saturation (Error: Reference source not found) and can be used to
diagnose and correct -waves in the lattice (section 3.2.3.2). Sextupole
correctors have the strength to overcome dipole saturation effects at
full energy (Error: Reference source not found) as well as regulation of
chromatic effects (section 3.2.2.3).

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

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 two 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 700 kg/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:

1.  Compact superconducting correctors with cold ferromagnetic screen
    \[[^29]\]

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

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

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

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

6.  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.

The six correctors in the 3.5 m space at each half-cell 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.

![](media/image12.wmf){width="5.174305555555556in"
height="2.8194444444444446in"}

Figure 5.12. Horizontal dipole correctors

![](media/image13.wmf){width="3.4in" height="2.261111111111111in"}

Figure 5.13. Quadrupole correctors.

![](media/image14.wmf){width="3.045138888888889in"
height="2.1972222222222224in"}

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 are quench protection
systems, cryogenics, current leads, and warm-to-cold transitions for
instrumentation and beam vacuum.

Error: Reference source not found shows a schematic of the interaction
region magnetic elements. Each interaction region spans a space of 6
half cells, from 21 meters to approximately 810 meters from the
interaction points. The interaction region consists of eight high
gradient "inner triplet" quadrupoles, four beam separation/recombination
warm 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/image15.wmf){width="6.491666666666666in"
height="2.7083333333333335in"}

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-
quadrupoles, with an aperture of 85 mm \[[^30]\], can be used as a
starting point to meet these requirements. The basic design as shown in
Error: Reference source not found has two Nb~3~Sn layers in a cos(2θ)
geometry, wound using the cable described in Error: Reference source not
found. The cable has a target critical current density of 3000 A/mm^2^
at 4.2 K, 12 T \[[^31]\]. Internal splices can be avoided using the
double pancake technique. The main characteristics of the magnetic
design are shown in Error: Reference source not found. 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 x 10^-6^, 1.6 x 10^-8^ and \<1.0 x 10^-9^. The relative
field error is lower than 1.1 x 10^‑5^, at 12.5 mm from the center on
the midplane. Iron saturation effects remain to be studied.

Table 5.6: Conductor Characteristics for LHC upgrade Low-Beta
Quadrupoles

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

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

  Strand diameter                            0.825 mm

  = Cu/nonCu                                 1.3

  Number of strands                          36

  Cable dimension                            (1.34 1.60) x 15.0 mm^2^

  Effective filament diameter                40 m
  ------------------------------------------ ----------------------------

![](media/image16.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
  -------------------------------------- --------------------------------

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 \[[^32]\] modified at Fermilab \[[^33]\] 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 can not 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 program.

A possible solution for the mechanical design is the one proposed for
the upgraded version of the LHC IR low-beta quadrupoles presented in
\[[^34]\]. 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. 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 magnetic elements need to be
"tunable" they require a special gallery to house their power supply and
electronics. 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
detectors 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 included 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 7 kA, 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), an energy extraction circuit and
bypass diodes are unnecessary. Instead, in the event of a detected
quench, protection heaters on all the magnets in a circuit will be
energized and the circuit power converter will be phased off.

As stated, inner triplet quadrupoles 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 two
6U VME crates. Thus a space of approximately 70 6U crates are required
for each side/IR.

The IR quadrupoles are cooled by 4.5 K helium. Since the operating
temperature and pressure differs from the transmission lines, they will
require separate transfer lines and cryogenic systems. The dynamic heat
load is approximately 600 Watts/side/IP or 2.4 kW for both interaction
regions \[[^35]\]. This heat load, if taken directly by the 4.5 K
helium, will require approximately ½ of a VLHC-1 cryo plant. This heat
load does not occur at the same time as ramping losses in the Tevatron
injector, and thus might be provided for by load shifting from
Fermilab's existing Central Helium Liquefier. Impact on the cryogenic
system is discussed in 5.2.1. Local heating in the quadrupoles could be
quite large due to the strong focusing elements (GL \~ 3000 T-m/m) which
sweep charged particles into the cold mass. 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 to supply the cryogens to the magnetic elements. This will include
voltage taps, strip heater leads, thermometry and other cryogenic
instrumentation. 25-30 kA HTS leads would be used to supply the
excitation currents.

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 and are included in the totals in section
5.2.2.4.

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 \[[^36]\].
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.

### 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 \[[^37]\] 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. Warm magnets are more tolerant than superconducting magnets
of the beam losses that occur in beam transfer and beam cleaning
insertions. No warm-to-cold transitions, gate valves, etc. are required
between the quadrupoles and the \~100 m 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 (Error: Reference source not
found), or at non-standard beam spacings as required by special
insertions. It easy for extracted beam lines to miss the warm quads due
to their low profile and absence of a cryostat. 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 150 mm
beam spacing and the required beam pipe size of 22 mm implies certain
restrictions on the achievable quadrupole field gradient. The chosen
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. Error:
Reference source not found summarizes the quadrupole features.

![](media/image17.wmf){width="6.397222222222222in"
height="2.4194444444444443in"}

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 150 mm, or larger.

Table 5.8. Straight Section Quadrupole Parameter List

  --------------------------------------------------------- -------------
  Number Required                                           456

  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,                                               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 {#beam-cross-over-section .unnumbered}

Two beam cross-over regions (Sec. 3.2.1.3) are needed to equalize the
circumference of the two side-by-side rings. 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 . 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
Error: Reference source not found.

The magnet length L~m~ and tilt angle 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 \~35 m and a tilt angle of 7.

![](media/image18.wmf){width="4.102083333333334in"
height="2.2680555555555557in"}

Figure 5.18. Beam cross-over region layout. See also section 3.2.1.3.

The total length of the beam cross-over magnetic system is about 150 m.
The magnet cross-section is shown in Error: Reference source not found.
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/image19.wmf){width="4.225in" height="2.7069444444444444in"}

Figure 5.19. Beam crossing dipole. This is energized by the 100 kA
transmission line.

To allow a 150-m gap for the tilted magnet installation, the cell
focusing was modified using different lengths of standard cell
quadrupoles. Quadrupole lengths were limited to 6 m by water cooling
considerations. The total length of quadrupoles installed in both rings
for each of the two cross-over sections is 143.6 m.

#### 5.1.5.3 Warm-Iron Magnets in the Interaction Region {#warm-iron-magnets-in-the-interaction-region .unnumbered}

As described in section 5.1.4, the IR straight section requires
horizontal beam manipulations to collide the beams at the IP. For this
purpose, so called "separation/recombination" dipoles, as shown in
Error: Reference source not found, 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.

The existing transmission line cable is used for excitation of these
magnets, and a 1.95 T maximum 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.

The two beams, initially separated by 150 mm, are simultaneously bent
together by the recombination dipole, whose cross section is similar to
the one shown in Error: Reference source not found. 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 Error: Reference source not found. The good field region
area for this dipole is 35 x 20 mm, which is enough to accommodate the
two shifted beams.

![](media/image20.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
transmission line and current return. The gap height is 26 mm. The
maximum force applied to the superconducting cable is about 65 kg/m at
full field. The magnet cross-section is similar to shown in Error:
Reference source not found 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 same dipole in the utility straight section where a
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 Error: Reference source not found. The total length of
quadrupoles in each of the two FNAL-site IR sections is 445.1 m.
Quadrupoles with lengths longer than 6.1 m will be segmented into two
magnets to limit water cooling requirements.

#### 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 including RF
cavities, instrumentation, injection, extraction and abort systems. At
the RF cavities the required beam separation is 460 mm. This is
accomplished with separation dipoles similar to those used in the IR
sections. At the input and the output of the section, these dipoles have
an air gap width that accommodates both beams. In the middle of the
section, individual separation dipoles are installed side-by-side in
both rings. The cross-section of the dipole can be found above (Error:
Reference source not found). The length of the dipoles in the utility
section is 25 m, which allows shifting each beam by 155 mm within the
242-m space as is shown in Error: Reference source not found below.

![](media/image21.wmf){width="3.9291666666666667in"
height="2.4895833333333335in"}

Figure 5.21. Utility straight section including injection, abort, and RF
cavities.

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 208 m. 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 needed.

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

The overall injection/extraction scheme of the machine is shown in
Error: Reference source not found. As described in Chapter 4, the
Tevatron is run bipolar and is used to inject protons both directions
into the collider rings. Beams for both collider rings are extracted
using two extraction systems installed at (for example) the B0 area. Two
identical 3 km transfer lines slope downward at 3% and end at the
corresponding collider downstream utility section where Lambertsons and
kickers inject the beam into the VLHC. In both utility sections the beam
is injected into the radially inside ring, with the outboard ring
reserved for extraction and abort.

![](media/image22.wmf){width="3.8506944444444446in"
height="1.7013888888888888in"}

Figure 5.22. Injection and beam abort system scheme

Downstream of the injection point it will be convenient to have an
internal beam absorber for transfer line commissioning and tests which
do not involve 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 intensity limits, air-cooling should be
sufficient. A few bunches of 10^9^ protons are sufficient for a good BPM
measurement.

The injection optics fit comfortably into the long 350-m drift in the
utility region. The injection uses a full-aperture kick so that the
Lambertsons do 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 an asymmetric design is not needed. The clearance at
the nearest quad (100 m away) is 160 mm, large enough to allow
unobstructed placement of standard quadrupoles on both the injected and
circulating beam lines. The vertical clearance at the RF station (300 m
from the Lambertsons) is 480 mm. 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 Error: Reference source
not found. The system is composed of 6 separate modules, each 1 m long.
A field strength of 0.05 T is used for this study, close to that used
for SSC injection system \[[^38]\] and similar kicker magnets at
Fermilab. The duration of the kick provided to the injected beam is \~20
sec and is defined by the length of the beam pulse extracted from the
Tevatron. The injection kicker requires a magnetic field switching time
of 150 nsec. This determines the minimum time separation between
successive injected batches.

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.

Fast edges on *both* the rising and falling edges are required. This
permits "box-car stacking" of a Tevatron batch in between two filled
batches. This gives the freedom needed to produce a "smoothed" filling
pattern (i.e. one without large low-frequency components that would
produce a time-dependent Laslett tune shift). See section 3.2.5.2. This
will require a more complicated pulser than a Thyratron PFN, and will
probably require a second Thyratron for the trailing edge. Ripple
requirements after the trailing edge will probably require a cleanup
kicker similar to one recently installed in the Tevatron.

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 (100 to 0%) (nsec)                   150

  Impedance ()                                   16.6

  Maximum current (kA)                           2.1

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

The injection Lambertson (Error: Reference source not found) steers the
injected beam into the vicinity of the circulating beam without
affecting the circulating orbit. Only a symmetric version is required
due to the small length and sagitta. 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 obtain good vacuum 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).

![](media/image23.wmf){width="4.778472222222222in"
height="3.027083333333333in"}

Figure 5.23. Injection Lambertson magnet.

The main parameters of the Lambertson are summarized in Error: Reference
source not found below.

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,                                               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, similar to the Lambertsons but without the
field free region, have been designed. The coil cross-section is the
same. Because the 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. The
rest of the magnet parameters are very close to those shown in Error:
Reference source not found.

In addition to vertically bending magnets, the transfer line may require
horizontal bending with an estimated total angle of 80 mrad (depending
on siting details). This bend can be made using the same type of
magnets. The total dipole length required for this bend in both transfer
lines is about 300 m.

There are 86 quadrupoles installed in the transfer line. Most of them
have a gradient of 40 T/m and a length of 1 m. Using a design similar to
described in chapter 5.1.5.1, and intermittent powering of about 0.8 kW
peak power per lens, we can employ air cooling. This results in about 10
C temperature rise at the surface of the magnet.

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
start to this study has been undertaken in \[[^39]\].

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

The abort magnet system consists of a kicker magnet, a Lambertson, a
beam sweeper magnet and defocusing quadrupoles. Beam Absorber design and
other system issues 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 machine ramps, the magnetic field of the abort kicker, Lambertson
and sweeper magnet must track the beam energy. For the Lambertson this
is accomplished automatically by energizing it with the transmission
line current. 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.

**Abort Kicker Magnets** switch the beam between the circulating orbit
and the abort channel. Their 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 is 30 m. The cross-section of the kicker is shown in Error:
Reference source not found.

![](media/image24.wmf){width="3.7125in" height="2.0208333333333335in"}

Figure 5.24. Abort System Kicker Magnet

The current rise time in the extraction kicker is about 3 sec, so a beam
abort gap of about 3 sec is needed. This requirement results in using a
medium-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
the windings and ceramic vacuum pipe are installed inside. At nominal
field of 0.2 T the current is 2410 A. Maximum 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 %, more than good enough for this
device. In the configuration shown, the magnet inductance is 2.5 H/m.
Ten 3-m sections are used, installed one following another, with each
section having 7.5 H 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 the flat top level. For
the three-meter section, a discharge capacitor with C = 0.5 F provides
the needed current rise time. This results in maximum voltage at the
first stage of 9600 V. Energy stored in the capacitor bank or in the
magnetic field is about 25 J. The flat top length for the abort kicker
magnet is defined by the ring circumference and is about 800 sec. To
have this long pulse shape, a separate power source must be switched on
when current in the primary circuit starts to decay. This is a typical
long-pulse pulser implementation (see, for example, \[Error: Reference
source not found\]).

**Large Aperture Quadrupoles** are required between the Abort Kicker and
the Lambertson to allow for the 17-mm radial displacement at the
Lambertson (see Error: Reference source not found). This larger aperture
means that a lower field gradient of about 45 T/m can be achieved, and
longer quadrupole lengths are required for 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. Error: Reference source not found summarizes the large aperture
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                                  11.7 x 11.7

  Conductor cross section area, mm^2^                 104

  Resistance,                                         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 (C)                          16

  Water flow per magnet (liter/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 Error: Reference source not found. 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 in more
than 200 mm of beam separation at the downstream quadrupole and
horizontal dipole. Magnetic forces on the transmission line conductor
are about 25 kg/m. This force can be handled by the standard
transmission line support spider.

![](media/image25.wmf){width="4.3in" height="3.0097222222222224in"}

Figure 5.25. The Abort Lambertson Magnet. This is energized by the
transmission line so that it automatically tracks the beam energy.

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% field
nonuniformity in the sweeping magnets. Sweeping magnets deflect the beam
in the X and Y directions with amplitudes that correspond to the beam
striking the dump block at a location close to its radial dimension. If
the phase difference between X and Y oscillations is 90, the 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 sec.
This requires a beam oscillation frequency of \~2 kHz. The integrated
strength of the sweeping magnets must be about 12 Tm in each coordinate.
A field strength of 0.3 T was chosen for this device, resulting in a 40
m magnet. The required aperture 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 Error: Reference source not found. Field uniformity in
this magnet is at an acceptable level of about 5% at reference radius of
15 mm. A positive sextupole component in the whole aperture results in
additional beam defocusing on the target. The 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. The main parameters of the
magnet are summarized in Error: Reference source not found.

![](media/image26.wmf){width="4.238194444444445in" height="3.08125in"}

Figure 5.26. Sweeping magnet cross-section.

For equipment safety reasons the sweeping magnet is made of 10 separate
4-m sections powered by independent pulsers. The simultaneous failure of
two sections, which is a very low probability event, will not compromize
the safety of the absorber core. For each section, the current in the
magnet windings is supplied by a simple pulser that discharges a
capacitor bank into the windings. For each 4-meter section, the
capacitance required to have an oscillation frequency of 2000 Hz is
about 20 F. With a circuit impedance of 4 and resistance of windings at
2 kHz of about 0.1 , one can expect periodic oscillations 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, to ensure a better
beam energy distribution across the dump block surface. Peak voltage is
about 8 kV, requiring at least a 12 kV rating on the windings and
capacitor bank to ensure high reliability of the system. SCRs with
conservative ratings can be used at these values of voltage, current,
and repetition rate.

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                                 H             2 x 80
  ------------------------------------------ ------------- ---------------

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

Construction of the Stage-1 VLHC 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 they 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
Error: Reference source not found.

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 in at subcontractor
facilities off site 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 65-m 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 Error: Reference source not
found. 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-m long
iron core subassemblies to individual small parts. The space is
sufficient to house stock for at least three months of production. The
actual amount of storage needed will depend on vendor location and
capabilities. 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 a specific
operation. Each area will work autonomously and have the capability of
locally storing one week's production, so that glitches in one
manufacturing 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. Error: Reference source not found 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 \[[^40]\].

The factory will have special handling requirements. Since the magnets
and their subassemblies are 65 m 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. Error:
Reference source not found shows, schematically, an elevation of a
section of the plant, showing the workstations in nine areas.

![](media/image27.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.
Installation is not expected to begin until some time after magnet
production is underway. 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). 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.

Table 5.15. Assembly area and tooling summary

![](media/image28.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.

Error: Reference source not found 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 Error: Reference source not found are
accomplished in two, 8 hour shifts per day.

Reference \[[^41]\] shows detailed schedules for each sub-assembly
manufactured for the transmission line magnet, with a breakdown of
elapsed time 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. Error: Reference source not found 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
\[Error: Reference source not found\].

##### 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 six 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 60 K 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, wrapping
superinsulation, 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
\[Error: Reference source not found\].

##### 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. The 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 6.5 K flow return pipes, the 40 K shield supply header, and the
70 K 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 \[Error:
Reference source not found\]. 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 4.5 K with connection to 6.5 K. 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-m 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 12-m sections in
industry and supplied to the final assembly site for assembly in the
65‑m 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 70 K 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-m long
extrusions. Two pieces must be seam welded together to make the final
assembly \[Error: Reference source not found\]. 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 warm, either magnetically or with mechanical
measurements of the pole tip profile and alignment. Cold testing will be
performed on a limited 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 from 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 the Structural Support and
installed from the sides at Area #14. On half of 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. See Error: Reference
source not found and section 5.2.4.1. The completed magnet is then
transported to the storage area to await installation into the tunnel.

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

We focus discussion on testing of the combined function magnets during
production since these magnets are the dominant element of the Stage-1
machine. Because of their length and small bore, these combined function
C-magnets are also the most difficult to measure. Measurement and
testing of other magnetic elements in the ring are can be accommodated
by existing equipment and approaches.

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.

Warm 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 magnetic 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 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.[^42] 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 \[Error: Reference source
not found\]. This requires that the radius of the probe be known with
high accuracy. Typical manufacturing and measurement uncertainty for
coil placement in magnetic measurement apparatus is \~0.001 inch (25 m)
which translates into a field error of 0.3% for a probe of 10 mm maximum
radius. At least an order of magnitude greater precision (0.03% 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.[^43] 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 referenced 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 to the required accuracy 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 Error: Reference source
not found. Principle elements of the design are the following:

-   The probe body is clamped to a precisely machined fixture
    ('strong-back') on an edge which follows 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="4.220833333333333in"
height="2.932638888888889in"}

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 \[[^44]\] 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 \[Error: Reference source not
found\]. 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 \[Error: Reference source not
found\]. 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 \[[^45]\]
and LHC magnets \[[^46]\] 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. Cooldown and warmup times are short (about an
hour) due to the low cold mass, so testing time will be dominated by
setup and measurement times. If an accurate measurement of the heat leak
is required, it may take a couple of days for the multilayer insulation
and vacuum to stabilize.

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.

### 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 230-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, local 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 with the majority of subassembly installation and test work
    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 540 m), 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. Since the second stage
High Field Ring will modify tunnel layout, we must consider this upgrade
while planning the stage-1 work so that installed equipment will not
make this upgrade too complicated. a Tunnel cross section with both Low
Field and High Field accelerators installed is shown in Error: Reference
source not found.

![](media/image32.wmf){width="4.509027777777778in"
height="4.329861111111111in"}

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
alignment of 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 (10 km) 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 135 m. 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 with positions known to 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 \[[^47]\] and also chosen for the LHC \[[^48]\].
An overhead enclosed safety rail \[[^49]\] operating at 400-750 VDC
\[[^50]\] 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 30 kW assuming a
total vehicle weight of 50 tons, a rolling coefficient of friction of
0.02 \[Error: Reference source not found\], a drive train efficiency of
85% and a peak speed of 2.5 m/sec (9 km/h). Trolley power up to 100 kW
is supplied at the 10 km alcoves, allowing up to three vehicles to
operate simultaneously in each 10 km sector. Copper conductors \~1 cm^2^
are required in the rail to limit line losses to \<10%. Details of the
magnet transportation vehicles are discussed in the next section.

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 5 km to the personnel
egress points.

Personnel transport vehicles similar to \[Error: Reference source not
found\] 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 from the factory 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 local static deformation and torsion of the magnet
are shown in Error: Reference source not found. In the first 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 6 m away at the position of the adjacent magnet supports.

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

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

Taking into account its length, the magnet structure is quite flexible.
The vertical sag can exceed the safe limits from the above table, just
due to its own weight, if one of the supports is removed. On the other
hand, a smooth continuous bend with 1 km radius of curvature produces a
50 cm sagitta in the magnet with acceptable internal stresses. To
significantly reduce the risk of magnet damage during transportation, a
60 m long aluminum "lifting fixture" frame is used. The frame increases
overall rigidity and protects the magnet from vertical bending damage.
Error: Reference source not found shows the frame moving inside the
tunnel. Error: Reference source not found shows the "A-Frame" structure
of the beam that permits it to be either lifted or driven off of 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. The major load is taken by the two sets of wheels at the
25% and 75% points, with other smaller wheels to damp oscillations.

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 Error:
Reference source not found. 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 15 kW, pull the frame during
transportation from production facility to the designated location in
the tunnel. An alternative (chosen by the SSC and LHC) is to use a
general-purpose towing tractor pulling a passive magnet trailer. This
allows the towing vehicle to be used as an emergency egress vehicle if
the personnel transporter fails.

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 that sense nearby
walls 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 \[[^51]\].

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

The installation scheme shown in Error: Reference source not found
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 that 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.

Magnets are driven to their location along the beam line and put on the
support blocks without any transverse movement (Error: Reference source
not foundb). 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 67-m magnets in each half-cell must be
connected to form a common electrical, cryogenic and vacuum system. See
the right-hand side of Error: Reference source not found. 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 (Error: Reference source
not found) 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.

![](media/image35.png){width="6.3909722222222225in"
height="1.7722222222222221in"}

![](media/image36.png){width="6.3909722222222225in"
height="1.7722222222222221in"}

Figure 5.33. Splice of 100 kA conductor on 17 m test loop. Top: soldered
spiral-wrapped cables. Bottom: completed interconnection after weld and
leak check complete.

The basic steps of this procedure are listed below:

-   connection of the transmission line inner Invar pipes for both drive
    and return lines

-   splicing of the superconducting cables

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

-   connection of cryogenic piping

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

#### 5.1.8.6 Corrector Magnet Skids {#corrector-magnet-skids .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
135 m). These magnets are factory assembled and pre-aligned on a 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. A description of the correctors can be found in Section 5.1.3.
A total of 1568 corrector blocks will be transported and installed. A
single magnet transport vehicle can carry 16 skids, so \~100 trips are
required. 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 in an otherwise complete arc. In this case
the magnet will be transported parallel to the magnets that have already
been installed (Error: Reference source not found 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 that 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/image37.wmf){width="5.988888888888889in"
height="1.4722222222222223in"}

Figure 5.34. Magnet replacement scheme.

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

-   backfill the beam and insulating vacuum sectors with dry nitrogen
    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 65 m magnet is bent in the horizontal plane to
the radial position predefined by the pre-aligned support stands. The
force necessary to establish the 1.6 cm sagitta is less than 10 kg. It
is assumed that the 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 r.m.s. or less per adjuster. Conventional optical
techniques (theodolites and laser trackers) for alignment 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
± 3 mm 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, a
*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 ±3 cm 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 (± 1 cm maximum) over a 20-year lifetime.

**Vertical alignment** can be made using a hydrostatic leveling
technique, which makes use of fluid-filled containers with capacitive
readouts. This technique allows vertical alignment within ± 100 m for
each magnet. For larger scale, corrections taking into the account
non-uniformity in the Earth's gravitational 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 a technique similar to the one
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 the desired
accuracy. Alignment of the entire 65-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 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 non-critical but the Lambertson
septa must be accurately aligned.

pulsed injection and abort kicker magnets and abort sweep-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 quadrupole will weigh
about 25 tons 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 is 100 m 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 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 in four directions simultaneously. If
magnet replacement is required after the magnet string is installed, a
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 distance 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 the
total 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 a pressure
test, relieve valve setting tests, magnet string cooling down, heat
leakage test, and transmission line current test. Cold vacuum leaks
could be detected at this point. cryogenic plant performance and magnet
string quench tests will be also conducted.

A temporary installation of the 100 kA holding supply and current leads
(Error: Reference source not found) easily fits in the underground
caverns eventually intended for the Stage-2 dump resistors. The 2.5 V
holding supply will ramp a 20 km magnet string to 100 kA 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
the 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 collider ring commissioning.

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

The systems 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,
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. 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. Error: Reference source not found shows the
temperature profile in the transmission line.

A rough comparison of the cryogenics of various machines, normalized to
beam energy, is given in Error: Reference source not found. For this
comparison, the refrigeration for the SSC operating at L=10^34^ was
crudely estimated by tripling the dynamic heat load (\~2x overall
increase). The VLHC‑1 cryogenic system is significantly simpler and
lower-powered than the LHC or SSC systems.

Table 5.18. Comparison of Cryogenics Per TeV Beam Energy for Various
Machines.

  ---------------------- ---------- -------------- ---------- --------- ----------------- ----------------- ------------
                                    **Tevatron**   **HERA**   **LHC**   **SSC(10^33^)**   **SSC(10^34)^**   **VLHC-1**

  **Refrigeration (4.5 K kW/TeV     27             38         21        10                20                4
  eqv.)/TeV**                                                                                               

  **Helium               tons/TeV   4              21         14        16                16                4
  Inventory/TeV**                                                                                           

  **Cold Mass/TeV**      tons/TeV   600            5000       5,143     5,000             5,000             286

  **Magnetic Stored      MJ/TeV     400            1000       1,629     600               600               171
  Energy/TeV**                                                                                              
  ---------------------- ---------- -------------- ---------- --------- ----------------- ----------------- ------------

As shown in Error: Reference source not found, 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 19 km long. Each string is sub-divided into two loops, referred
to as "near" and "far" loops.

![](media/image38.wmf){width="5.080555555555556in"
height="4.9631944444444445in"}

Figure 5.35. Cryogenic layout of the Stage-1 VLHC. Six plants are spaced
at 38 km intervals around the ring. Each plant provides refrigeration
equivalent to 9.6 kW at 4.5 K. Nominal operating wall power is 2 MW at
each plant. One plant is on-site at Fermilab and has additional capacity
for detectors, IRs, RF, and superconducting current leads.

![](media/image39.png)

Figure 5.36. Temperature profile of the supercritical flow in the VLHC
transmission line.

##### 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.

###### Cryogenic Valve Boxes {#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.

###### Transfer Lines {#transfer-lines .unnumbered}

Transfer lines are a part of the magnet assembly. A line contains five
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 a 0.102 m OD stainless steel pipe connected
    to an extruded aluminum shield that surrounds all the inner lines.
    The shield is wrapped with 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 that are also anchored at the midpoint of the
    module. These lines are of concentric design. The 6.0 K helium flows
    between two 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 circuits are located every 540
meters, as seen in Error: Reference source not found. 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 the
atmosphere.

![](media/image40.wmf){width="6.145138888888889in"
height="2.602777777777778in"}

Figure 5.37. Helium shield flow and pressure relief valves.

Quench protection of the transmission line is discussed in sections
5.1.2.2 and 5.2.2.3. 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,
should 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 40 K 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 70 K and
1.3 MPa (13 bar). Flow is supplied via a 0.089 m OD tube and distributed
via a pair of 6 mm 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 components:
the primary heat load on the 4.5 K system and the heat load to the 40 K
shield system. The calculated heat loads are presented in Error:
Reference source not found.

Table 5.19. VLHC Design Study Calculated Transmission Line Heat Loads

![](media/image41.wmf)

##### 5.2.1.1.5 Cryogenic Loads for On-Site Refrigeration Plant {#cryogenic-loads-for-on-site-refrigeration-plant .unnumbered}

The extra loads for the on-site refrigeration plant are summarized in
Error: Reference source not found. The total refrigeration power (4.5 K
equivalent) is comparable to a single additional cryo plant.

Table 5.20. Extra loads for the on-site refrigeration plant.

  ------------------------------ ------------ ------------- ------------ ----------------
                                 **4.5 K      **4.5 K       **40 K       **Liquefaction
                                 (static)**   (dynamic)**   (shield)**   (g/s)**

  Current Leads (Sec. 5.2.2.2)   \-           \-            \-           15 g/s

  IR Beam Debris (Sec. 5.1.4.2)  \-           2.4 kW        0.5 kW       

  IR Static Heat Load (rough     0.5 kW       \-            10 kW        
  est.)                                                                  

  RF Cavities (Sec. 5.2.6)       0.48 kW      1.76 kW       \-           

  On-site Transfer Lines (6 km)  0.2 kW       \-            12 kW        

  **TOTAL**                      1.2 kW       4.2 kW        25 kW        15 g/s
  ------------------------------ ------------ ------------- ------------ ----------------

It is notable that most of the on-site cryogenic loads are dynamic and
are not present during the injection cycle when the Tevatron is ramping.
It is therefore plausible that most or all of the on-site cryogenic load
could be serviced by load shifting from the existing Fermilab Central
Helium Liquefier.

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

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

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 5.21. Predicted power requirements for ring cryogenics

![](media/image42.wmf)

Error: Reference source not found shows the refrigeration process
schematic. 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 a 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 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/image43.wmf){width="4.357638888888889in"
height="5.240277777777778in"}

Figure 5.38. Refrigeration Process Flow and Transmission Line flow
schematic. A split cold box similar to LEP is used to make the process
insensitive to altitude changes between the tunnel and surface. The
transmission line flows extend ±19 km from the cryo plants. The flow is
split into two parallel loops: the "near" loops that extend ±9.5 km from
the cryo plant, and the "far" loops that service magnets between 9.5 km
and 19 km from the cryo plants.

These plants are well within existing commercial vendor capabilities.
They are simpler but technologically similar to those of LEP, LHC, SNS,
and HERA, and 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 type, 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 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 times the Tevatron inventory. Each
cryogenic plant will have three 37.8 m^3^ liquid helium storage dewars,
and fifteen gas tanks capacity of 113.6 m^3^. 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 local control of the cryogenic hardware in the event
that a 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 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
Error: Reference source not found.

![](media/image44.png)

Figure 5.39. Flow schematic of the 38 km 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 steps. First, each
sector will be pumped and backfilled five 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 \< 5 ppm. 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 stages. The first stage
involves the cool down of the helium plants. The second stage is the
cool down of the transmission line to 40 K. Finally the transmission
line will be cooled 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 set up
in the liquefaction mode and 40 K 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 out from the
refrigerator through the near loop transmission line, the 6.5 K return,
the current return bus, and the shield circuits, and then returns via
the warm header. When the temperature at the end of the "near" loop
(measured at the valve box) is 70 K the flow is then re-directed to the
"far" loop and into the return header. As the "far" loop temperature
reaches 70 K the second cooldown stage can be started.

During the third cool down stage, the plant is re-tuned for an outlet
temperature of 4.5 K. The flow pattern for the second stage is the same
as the first stage. As the temperature for each loop is at 7 K 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 Error: Reference source not
found below. The major item is the single 100 kA 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 5.22. Power Supply, Current Leads and Quench Protection Summary
for Stage-1 Machine

+---------------+-------------+-------------+------------+------------+
|               | T           | IR          | Straight   | Corrector  |
|               | ransmission | 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          | 10 V typ.   | 1000 V     | 100 Typ    |
| supply        |             |             | typ.       |            |
+---------------+-------------+-------------+------------+------------+
| Current per   | 100 kA      | 25 kA       | 200 A typ  | 2 A 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    | 20 km       | h           |            |            |
|               |             | eaters/quad |            |            |
+---------------+-------------+-------------+------------+------------+
| SC Current    | 100 kA-pair | 60 kA-pair  | \-         | \-         |
| leads         |             |             |            |            |
+---------------+-------------+-------------+------------+------------+
| **Peak        | **17.7 MW** |             |            |            |
| Ramping       |             |             |            |            |
| Supply        |             |             |            |            |
| Power**       |             |             |            |            |
+---------------+-------------+-------------+------------+------------+
| **Total Power | **10.5 MW** |             |            |            |
| Supply**      |             |             |            |            |
|               |             |             |            |            |
| **Power in    |             |             |            |            |
| Collision**   |             |             |            |            |
+---------------+-------------+-------------+------------+------------+

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

The low inductance (3 H/m, 0.6 H ring total) and low stored energy
(10 kJ/m, 3 GJ total) of the single-turn transmission line magnet allow
the entire ring to be powered from a single supply \[[^52]\]. See Error:
Reference source not found. A voltage of 62 V ramps the machine up or
down in 1000 seconds. The design current of 100 kA at flattop exceeds
the 87.5 kA 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 ft 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 \[[^53]\].

The power supply is actually two supplies in series. The main ramping
supply generates the positive or negative voltage to transfer 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.

![](media/image45.png){width="5.54375in" height="3.7958333333333334in"}

Figure 5.40. 100 kA Power Supply and Quench Protection For Transmission
Line Magnets

The Main Ramping Supply design (Error: Reference source not found) is
based on paralleling 8500 A 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 10 kA 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 (6.2 MVA) 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 4,800 KVA is less
than one feeder cable for the source.

![](media/image46.wmf){width="6.5in" height="1.9520833333333334in"}

Figure 5.41. 100 kA Ramping Supply Schematic (one 2 x 8.5 kA module
shown)

The +2.5 V holding supply is essentially a copy of the 100 kA switching
converter \[[^54]\] constructed for the R&D magnet test. The device
consists of a 450 VDC, 500 kW bulk supply followed by ten 10 kA DC-DC
converter modules in parallel. This two-stage regulation scheme provides
immunity to variations in input line voltage. The modules use IGBT
chopper bridges, tape-wound cores and Schottky power diodes. The
switching frequency is \~2 kHz. To minimize output ripple the 10 modules
are phased to switch sequentially. This pushes the fundamental ripple
frequency up to 10x the switching frequency or \~20 kHz. 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. A single pair of 100 kA
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 \[Error: Reference
source not found\], or could be a specially built High-Temperature
Superconductor (HTS) version using the 50 K transmission line shield
flow as the inter-stage temperature. The cryogenic wall power associated
with the conventional 100 kA leads is approximately 300 kW. This could
be reduced by a factor of 4 with HTS leads \[[^55]\]. Payback time for
the electrical cost savings from HTS leads is approximately 3 years.

![](media/image47.png){width="5.213888888888889in"
height="3.209722222222222in"}

Figure 5.42. 100 kA 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 and used for partial-ring commissioning.

IR quadrupoles can use commercially available HTS leads similar to the
LHC. The total requirement for current leads in the Stage-1 machine is
about 150 kA-pair, or about 1/12^th^ of the current leads required by
the LHC.

#### 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. Quenches are detected by a voltage imbalance
at the power supply (Error: Reference source not found). When a quench
is detected, magnetic energy is extracted with a 1-second L/R time
constant by cryogenic "dump resistors" spaced at 20 km 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
5.1.2.2. Quench protection system parameters are given in Error:
Reference source not found. The theory of operation is explained in
\[[^56]\] and a detailed write-up is given in \[[^57]\].

![](media/image48.wmf){width="5.75in" height="1.8743055555555554in"}

Figure 5.43. 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"\[[^58]\]
which has a high normal state resistance. Current is transferred to a
thick-walled Invar pipe that 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 100 kA 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.

It is instructive to compare this quench protection system to those of
other accelerators. The LHC for example \[[^59]\] 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.

Table 5.23. Stage-1 Quench Detection and Protection Parameters.

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

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

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

  Energy Dump Time Constant           1 second

  Peak Voltage To Ground during Dump  3 kV

  I^2^t during dump                   5 x 10^9^ A^2^s

  Peak Temperature of Conductor       250 K
  During Quench                       

  Peak Pressure of Helium During      35 Bar
  Quench                              

  Pressure relief during quench       Every 2 cells (500 m)

  Effective Copper Cross Section of   3 cm^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 m per location,

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

  Dump Switches                       Quenched superconducting cables
                                      65 m long

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

  Cryogenic Dump Resistor Thermal     65-m long, 3-cm ID, 5.5-cm OD Invar
  Mass                                pipe

  Final Dump Temperature after Dump   325 K
  from 100 kA                         

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

#### 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 \~500 kW 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 \[[^60]\].

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.

#### 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
\[Error: Reference source not found\] and summarized in Error: Reference
source not found. 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.

Table 5.24. 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     |           | **18750**  | **19150**     |
|       | Total**           |           |            |               |
+-------+-------------------+-----------+------------+---------------+

The layout of the LCW system is sketched in Error: Reference source not
found. 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/image49.wmf)

Figure 5.44. 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.

### 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 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 "half-cell locations" (every 135 m 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 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 failure of a handful of
local electronics modules will not require immediate maintenance.

![](media/image50.wmf){width="3.047222222222222in" height="2.275in"}
![](media/image51.png){width="3.1840277777777777in"
height="2.283333333333333in"}

Figure 5.45. Electronics module at each quad location (every 135 m)
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. Cryogenic thermometry and a
valve controller are used at every other quad location (270 m) to
regulate the 50 K shield flow. Every 10 km 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 180 cm^2^
\[[^61]\]. 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 (Error: Reference source not
found) at each half-cell 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/image52.wmf){width="6.104166666666667in"
height="3.2305555555555556in"}

Figure 5.46. Cabling Layout on the Transmission Line Magnet. Cables and
instrumentation are preinstalled and factory-tested on the 65 m magnets.
Each magnet has a 5 m "extension cord" which jumpers to an electronics
module located in a hole in the wall\
at each half-cell location (135 m spacing).

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

The warm (air-cooled copper) correction magnets (Sec. 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 1400 W. Average corrector power is \< 1000 W in a
realistic operating scenario. At maximum current approximately 90% of
the power is dissipated in the magnets themselves with the remaining 10%
(\~150 W) in the power supply converters. Instrumentation and control
power at each quad location is estimated to be \~100 W for a total of
250 W dissipated in the module. Power at this level can be passively
carried away from the electronics (Error: Reference source not found)
via a heat pipe \[[^62]\] and removed by the tunnel airflow of
\~1 m/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 1 kV DC feeders that loop the ring (see Error: Reference
source not found). 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/image53.wmf)

Figure 5.47. DC Power Distribution Scheme in Arcs. Redundant Bulk DC
supplies in walk-in alcoves every 10 km 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 1 kV DC is chosen for power distribution to the
electronics modules at each quad location. The DC is provided by 100 A
bulk supplies every 10 km 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 25 A 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 10 km 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" \[[^63]\].

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
local electronics modules. Modern DC-DC converters \[[^64]\] have the
following parameters: power density 200 W/in^3^, efficiency \~90%, cost
\~\$0.35/watt. In fact, essentially all modern AC devices (e.g.,
fluorescent light ballasts, computers, high current welders, motor
controllers) rectify the AC line power and then chop the signal using
DC-DC techniques. Rectification at 60 Hz 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,
the effects of power supply noise on emittance growth can be essentially
eliminated as discussed in section 5.2.2.1.

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

Both X and Y BPMs (Error: Reference source not found) will be provided
every 135 m at the corrector region at each half-cell boundary (Error:
Reference source not found). Although measurement of the second
coordinate only improves the closed-orbit distortion by 10% \[[^65]\],
the added redundancy obtained by an independent readout of both
coordinates 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
\< 1 mm this is not a problem. In a few special locations near beam
transfers where off-axis orbits must be measured, split-plate BPMs with
better linearity will be used.

The BPM calibration offset can be verified *in situ* using the
independently powered quadrupole correctors at each half-cell. The BPM
can be accurately fiducialized to the warm iron of the corrector. At
injection energy, the quad steering associated with a 1 mm orbit offset
through the corrector generates an easily measured 3 mm orbit distortion
as the corrector is powered.

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 that also
included calibration circuitry \[[^66]\].

Digitization bandwidth is determined by the first turn and transient
response desired. A digitization rate \>25 MHz 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 20 m least
count resolution. Power dissipation for 4 channels of 10-bit 40 MHz
digitization would be 300 mW total \[[^67]\].

The cable run from the BPM to the local electronics module is about 5 m.
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/image54.wmf)
![](media/image55.png){width="2.7958333333333334in"
height="3.203472222222222in"}

Figure 5.48. 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 and 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. This 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 (Error:
Reference source not found) 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. This will provide complete BLM 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 2 kV/100 A
Cockroft-Walton DC-DC converter module, an op‑amp integrator, and a
medium bandwidth \~100 kHz 14-bit ADC. Power dissipation should be \<2
W.

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

Each 135 m half-cell contains 12 ion pumps (22.5 m pump spacing in each
bore). These are powered and read out from the local electronics module.
Each pump requires a 5 kV supply with a starting current of up to 30 mA
but an operating current less than 0.1 mA. The power for all 12 pumps is
provided by a single transformerless bulk supply (a 5-stage
Cockroft-Walton converter operating from the 1 kV DC 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
Digital Signal Processor (DSP). Vacuum gauge readout for the beam and
insulating vacuum will also be incorporated into the local electronics
module.

Failure of the bulk supply shuts down all ion pumps in a 135-m
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 and \< 1% drop in the overall beam lifetime. 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 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.
These 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
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 10 km alcoves. The fiber cable
will be a pre-assembled harness 5 km long with 4-fiber breakouts at quad
locations every 135 m. Installation will consist of laying the fiber
harness in the cable tray immediately below the electronics modules
(Error: Reference source not found) and plugging the breakout into each
electronics module.

![](media/image56.wmf)

Figure 5.49. Fiberoptic Clock and Network Connections in the tunnel,
including redundant hubs and clock fanouts at 10 km alcoves.

The long-haul fiber backbone interconnecting the 10 km 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 (see sect 5.3.3.2).

#### 5.2.3.9 Local Electronics Module Miscellaneous Functions {#local-electronics-module-miscellaneous-functions .unnumbered}

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

-   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 and water problems

-   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).

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

The beam vacuum system is divided into two sections. In the 225 km of
transmission line magnets an extruded-aluminum warm vacuum system
similar to LEP and electron storage rings is used. In the 8 km 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/image57.png){width="6.145833333333333in"
height="4.128472222222222in"}

Figure 5.50. 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 (Error: Reference source not found)
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 22.5 m. 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 in
\[[^68],[^69]\]. Inputs to the calculation included: 1) the measured
synchrotron-induced desorption of major gas species from aluminum
\[[^70]\] 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 \[[^71]\], 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 \[[^72]\]. The result of
the calculation (Error: Reference source not found) 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/image58.wmf){width="4.261805555555555in"
height="3.3645833333333335in"}

Figure 5.51. Beam scrubbing scenario for Stage-1 aluminum vacuum
chamber. During the first 5 fills the beam current is increased from
50 mA to the design value of 190 mA. 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 65 m lengths
of extruded pipe which are installed in the magnets, cabled, and tested
at the factory. Beam pipe extrusions 12 m in length will be received,
inspected, and cleaned using an environmentally safe alkaline cleaning
procedure developed at the APS at Argonne and used on the Fermilab
Recycler \[[^73]\]. The sections will be welded together to form 65 m
lengths that include the Ion Pumps, NEG strips, feed-throughs and end
transition sections. The assembly will be sealed, pumped and baked at
200C for 12 hours in a 65 m 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 (Error:
Reference source not found) 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 \[[^74]\] in ANSYS and stresses
are acceptable even for annealed aluminum.

![](media/image59.wmf){width="3.63125in" height="3.115972222222222in"}

Figure 5.52. 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 \[[^75]\], and gains very little after the
beam scrubbing has completed \[[^76]\]. A similar conclusion has been
reached at the ELETTRA light source \[[^77]\]. 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 8 km 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, alignment,
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.

### 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 at 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 150 m, the
beam pipes are separated by \~45 cm 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. These are discussed more
fully in \[[^78]\].

Table 5.25. 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           
  ------------------------- ------------- --------------- --------------------------

### 5.2.6 Radio Frequency Systems  {#radio-frequency-systems .unnumbered}

Either superconducting or warm copper cavities produce workable RF
acceleration systems for the Stage-1 machine \[[^79]\]. During the
design study acceptable parameters and costs based on the B-factory RF
systems were developed \[[^80]\]. 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 Error: Reference source not found. 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 \[[^81],[^82]\], but with somewhat relaxed
requirements for 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 \[[^83]\]
and tests of LHC \[Error: Reference source not found\] and SOLEIL
\[[^84]\] cavities show that it is reasonable to expect operating
gradients as high as 8 MV/m. For VLHC we chose a gradient of 7.75 MV/m
(3.125 MV per cell). Sixteen single-cell superconducting cavities are
needed for each beam in the Stage-1 machine and 64 cavities are needed
for each beam in the 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 a very strong periodic modulation of RF phase of 27 for
Stage-1 and 10 for Stage-2. This modulation is larger than at the LHC. A
special RF feedback loop around the amplifier-cavity system assisted by
the programmed phase modulation *a la* LHC \[[^85]\] will be necessary
to suppress this effect.

Each cryomodule will accommodate four single-cell cavities with
cell-to-cell distance of 3/2. The overall length of the cryomodule is
approximately 5.6 m. The static heat leak of the cryomodule is 60 W and
the RF cavity wall losses are 55 W/cavity, which yields a total
cryogenic load of 280 W per cryomodule. The 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 the 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 jointly developed and constructed
recently by CERN and SLAC for testing LHC cavities \[[^86]\]. The
klystron has a high efficiency of 68% and thus the 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 total for both beams.

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

To estimate the cost of Stage-1 cryomodules we will use the formula
\[[^87]\]

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

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 4.2 M\$. The RF chain
cost (including klystrons, high voltage power supplies, low level
electronics, and RF distribution) is \$1/W and totals to 8 M\$.

The VLHC RF system would greatly benefit from R&D on improving the
technology of sputtering niobium on copper with the goal to decrease if
not completely eliminate the phenomenon of the *Q* slope. Special
efforts should be devoted to understanding the nature of this effect.
Success of this R&D would allow an increase of the accelerating gradient
without seriously increasing the cryogenic heat load. Also, an 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 \[Error: Reference source not found\].

Table 5.26. 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  |          |
| (both beams)         |           |   |         |           |          |
+----------------------+-----------+---+---------+-----------+----------+
| Synch. rad. loss per |           |   | 0.03    |           | 12.37    |
| turn                 |           |   | MeV     |           | MeV      |
+----------------------+-----------+---+---------+-----------+----------+
| Total s.r. power     |           |   | 13 kW   |           | 2.1 MW   |
| (both 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 (753.1) | 371.7 MHz |   |         |           |          |
+----------------------+-----------+---+---------+-----------+----------+
| 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 | 210^9^    |   |         |           |          |
+----------------------+-----------+---+---------+-----------+----------+
| 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         |           |   |         |           |          |
+----------------------+-----------+---+---------+-----------+----------+

### 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 \[[^88]\]. 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 tune changes that might
be desired.

![](media/image60.wmf)

Figure 5.53. 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/image61.wmf)

Figure 5.54. 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 (sect. 3.2.1.4)
involve removing 5 m 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 -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 been
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 53.126.5 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

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

## 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 \[[^89]\]. 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 \[[^90]\]. The magnitude of the
problem has increased however. The beam of the Stage-1 machine carries
enough energy that in principle it could liquefy 400 liters of stainless
steel (whereas the LHC beam 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 a very
pessimistic scenario, since in reality 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 \[[^91],[^92]\] and the results are
summarized here.

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 that 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 that 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. 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 that absorb and diffuse the beam energy.
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 that has a length 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 \[[^93]\] and LHC \[[^94]\]. 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.

![](media/image62.wmf){width="6.270833333333333in"
height="2.938888888888889in"}

Figure 5.55. Schematic layout of beam abort channel including kickers,
Lambertson septa, extraction beam sweeping, beam window, sacrificial
rod, and graphite 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 300 kW average power (section 7.4.1)
corresponds to one full-energy abort of both beams every day and is
equal to the 300 kW design value for the Main Injector beam absorber.
The overall design is patterned on the Main Injector absorber that 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 1300-1500C (from
successful Tevatron dump experience and theoretical shock wave
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 1330C.
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 1500C. 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 \[[^95]\]. 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 Error:
Reference source not found. 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. No personnel safety issues are involved.

![](media/image63.png){width="3.0416666666666665in"
height="1.2777777777777777in"}

![](media/image64.png){width="3.140972222222222in"
height="0.6583333333333333in"}

![](media/image65.png){width="2.8006944444444444in"
height="1.1631944444444444in"}

![](media/image66.png){width="2.536111111111111in" height="1.15in"}

Figure 5.56. 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, x,y = 1.4 mm, *~inc~* = 0.7
mrad) and top energy (20 TeV, x,y = 0.3 mm, *~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 Error: Reference
source not found).

![](media/image67.png){width="3.0805555555555557in"
height="2.5861111111111112in"}
![](media/image68.wmf){width="2.5145833333333334in"
height="2.598611111111111in"}

Figure 5.57. 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. Error: Reference source not
found shows fast (1 msec) and slow (0.1 sec) beam loss rates needed to
initiate a SC magnet quench at injection and top energy in the Stage-1
ring. For comparison, the values for the Tevatron at 0.9 TeV are shown.
This comparison assumes that the quench limits are the same in the VLHC
conductor and the Tevatron dipoles. This assumption is probably
pessimistic since the braided cable of the VLHC can re-route the current
around a quenched region on the magnet midplane, whereas a cosine-theta
magnet cannot.

Table 5.27. Quench-Inducing Loss Thresholds (protons per pulse) for the
VLHC Stage-1 and Tevatron.

  ------------------ --------------------------- -------------------------
                     Fast Loss (ppp)             Slow Loss (ppp)

  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 5.2.1. The distributed heat load
from beam losses 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 (3.5 mW/m average). This is a 5% perturbation on the 5 K
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 \< 2 mW/m, less than 3% of
the 4.5 K heat load. If continued R&D reduces the 4.5 K heat leak this
will become an increasingly important part of the total.

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

Section 5.2.3 describes electronics housed in small enclosures ("holes
in the wall") at each quad location. This approach was studied at UNK
\[[^96]\] and the electronics was found to survive under rather
conservative assumptions about their radiation hardness. A recent
interesting development \[[^97]\] 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 \[[^98]\]. Depending on LHC operational experience, the
rather modest costs of the module enclosures might be saved by
eliminating the enclosures.

Radiation damage to fiber optics placed in the tunnel was studied at the
SSC \[[^99]\]. 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 the accelerator aperture because of
intra-beam scattering, small-angle beam-gas interactions along the
circumference, collisions in the IPs, RF noise, ground motion and
resonances excited by the accelerator imperfections. These continuously
generate a beam halo. As a result of beam halo interactions with
limiting apertures, hadronic and electromagnetic showers initiated 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
\[[^100],[^101]\]. The three-stage beam collimation system consists of 5
mm thick primary tungsten collimators placed at 7~x,y~ and 3 m long
copper secondary collimators located in an optimal phase advance at
9.2~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 14 ~x,y~ to intercept only
particles scattered out from the secondary collimators.

![](media/image69.png){width="2.654861111111111in"
height="3.5868055555555554in"}

Figure 5.58. Beam loss distribution along the accelerator at injection
(top) and at collisions (bottom).

![](media/image70.png){width="2.638888888888889in"
height="3.5395833333333333in"}

Figure 5.59. Beam loss distributions in the collimation section at
injection (top) and at collisions (bottom).

shows that the simulated performance of the system meets the goal of
essentially eliminating losses away from the cleaning insert. The main
reason for this excellent performance is that the system uses a lattice
insert specifically designed for this purpose, rather than something
that 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 beam cleaning system was designed with the goal of reducing losses
and detector backgrounds near the high luminosity insertions. Without
the supplementary collimators, about 61 W of beam power (2 x 10^7^
protons/sec) are lost upstream of the detectors. Including the
supplementary collimators in our calculations, however, 6 x 10^4^
particles are lost in the collimators, and we did not see any loses in
the vicinity of interaction point. Further investigations should be done
to determine ultimate particle backgrounds in the IP with the
collimation system.

The primary collimation insert will be located in a far side straight
section conjugate to the one of 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 20 kW 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 1 m of radial iron followed by 50 cm of radial concrete
over a length of \~15 m along the beam line 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 \[[^102]\], 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.

### 5.3.6 Worst-Case Beam Accidents {#worst-case-beam-accidents .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 the 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 (3-5 mrad).

A preliminary observation is that the nearby cryogenic piping would
rupture due to the rapid 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 \[[^103]\] 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 (Error: Reference source not
found) 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 15 cm in radius are heated to the melting
point of dolomite. Obviously it 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
that breaks off from thermal stress. The rise time of the heat pulse
(1 machine revolution or about 0.8 msec) allows the mechanical stresses
to relieve themselves on the scale of a couple of meters, so a static
mechanical analysis is approximately valid.

![](media/image71.png){width="2.748611111111111in" height="2.7125in"}
![](media/image72.png){width="2.5in" height="2.7131944444444445in"}

Figure 5.60. VLHC Stage-1 beam at 6.5 mrad grazing incidence on tunnel
wall. The left picture shows particle tracks; the right picture is a map
of energy deposition.

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) 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.

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

#### 5.3.7.1. Introduction {#introduction-1 .unnumbered}

The VLHC with its two stages present a number of important
considerations in the general area of environment, safety, and health.
It is the intent of this section to identify the character of these
challenges in a general way. Some of the considerations which must 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 novel issues have not been encountered on the same
scale and require particular attention to assure their timely resolution
in a manner that is cost-effective and that meets the approval of the
public. In this section, both the conventional and the novel issues are
discussed. 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.

#### 5.3.7.2. Procedural/Regulatory Matters {#proceduralregulatory-matters .unnumbered}

The actual design, construction, and operation of the VLHC will have to
meet a number of procedural/regulatory milestones to assure timely and
continued support by the public and by the Department of Energy. ES&H
requirements are currently set forth as a part of Fermilab\'s Work Smart
Standards, incorporated in the contract between the 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 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 \[[^104]\]. Of course, the contract under which Fermilab might
operate in the future is likely to change in ways that could modify the
applicable requirements.

##### A. Environmental Protection Procedural/Regulatory Matters {#a.-environmental-protection-proceduralregulatory-matters .unnumbered}

All DOE activities are subject to the requirements of DOE\'s regulations
for implementing the National Environmental Policy Act (NEPA)
\[[^105]\]. A new project of this magnitude 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. A
likely result will conclude that that the preparation of an
Environmental Impact Statement (EIS) is necessary since the VLHC extends
far beyond the present boundary of the Fermilab site. The EIS process is
generally considered to be an arduous one, but one that can be followed
to a successful conclusion. 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 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). Some of the Federal and State permits 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 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. Early
coordination with the project design team should greatly facilitate
completion of the associated milestones. The VLHC is likely to be
initially viewed by the public and by Federal and State regulators as a
poorly understood, esoteric technology. In recognition of this and also
because it will have an 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 facility.

##### B. Safety and Health Procedural/Regulatory Matters {#b.-safety-and-health-proceduralregulatory-matters .unnumbered}

In accordance with Fermilab\'s Work Smart Standards, the Laboratory will
be required to prepare an assessment of the ES&H issues associated with
this project in the form of a Safety Assessment Document (SAD). Given
the size, scope and cost of the VLHC, the preparation of a Preliminary
Safety Assessment Document (PSAD) is needed. The purpose of the PSAD is
to identify the relevant ES&H 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. It is nearly certain that DOE
will choose to review these safety documents by utilizing an external
review team. Just prior to facility operation, a readiness review will
be conducted in similar fashion using an external review team. 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.

#### 5.3.7.3. Occupational Safety During Construction {#occupational-safety-during-construction .unnumbered}

The VLHC requires a large amount of tunneling in bedrock units, most of
it horizontal or nearly so, and other tunnels 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.
Tunnel Boring Machines (TBMs) will be used for most of the tunnel. For
some portions of the underground facility the drill and blast method
will most economical. Both methods have associated occupational safety
considerations. Provisions for emergency response including underground
rescues will be needed. Egress issues relevant to protection of the
construction workers will be of paramount importance.

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 5.3.7.4). Downward slopes in the bedrock units will require
attention to the prevention of uncontrolled movements of heavy objects
downhill. While such control measures are well within those encountered
in mining operations elsewhere, they are novel at accelerator
laboratories.

During project construction, industrial radiography, a tool commonly
used in general industry, is likely to be employed to assure the quality
of pipe welds. 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. 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.

#### 5.3.7.4. Environmental Protection During the Construction {#environmental-protection-during-the-construction .unnumbered}

A small portion of the VLHC will be located near the surface, in the
glacial till, while most of it will be located deep underground in
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. 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 will result in a determination of
the impact of the project on wetlands and or floodplains. It may be
necessary for compensatory man-made wetlands to be created.

Tunneling in the bedrock units will result in the removal of a
considerable volume of rock. 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 reused at Fermilab or disposed. 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 off site. The placement of such a
project in any aquifers results in the need to protect drinking water
resources from contamination during construction. Also, the
\"de-watering\" of tunnels, as the construction proceeds will require
measures 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 \"de-watering\" 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. The exact depth of the
various aquifers is not known in detail at all locations and accurate
measurements will be needed. 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.

Tunneling activities can generate considerable noise and vibration. For
blasting techniques, 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.

#### 5.3.7.5. Occupational Safety During the Operations {#occupational-safety-during-the-operations .unnumbered}

##### A. \"Ordinary\" Occupational Safety Hazards {#a.-ordinary-occupational-safety-hazards .unnumbered}

In this section, the focus is on the issues that have been successfully
addressed before, at Fermilab and elsewhere by well-known techniques.

-   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.

-   Radio-Frequency (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, transformers and electrical switchgear will
    be installed underground. 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.

##### B. Novel Occupational Safety Hazards {#b.-novel-occupational-safety-hazards .unnumbered}

This section is directed to those occupational safety hazards that are
not generally encountered at accelerator facilities. These will require
consideration in the early planning stages in order to be addressed in
an efficient manner.

-   The VLHC requires the extensive use of superconducting materials and
    cryogens. While these technologies are relatively new, a number of
    accelerators worldwide 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).

-   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.

#### 5.3.7.6. Ionizing Radiation Safety During Operations {#ionizing-radiation-safety-during-operations .unnumbered}

##### A. Prompt Radiation Shielding {#a.-prompt-radiation-shielding .unnumbered}

The siting of the VLHC deep underground will provide adequate passive
shielding to attenuate prompt radiation to levels acceptable to the
members of the public. The shielding of proton accelerators needs to
attenuate 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 \[[^106]\], the shielding
requirements must be well-understand at the earliest possible stage in
the design and in the NEPA process.

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) \[Error: Reference source not
found,[^107]\]. 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. 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 non-occupational annual doses to 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.

##### B. Residual Radioactivity of Components {#b.-residual-radioactivity-of-components .unnumbered}

In the high-energy region, most, but not all, of the radiation effects
scale roughly with the beam power. In particular the effects of high
residual activity levels should be carefully taken into account at early
stages of design of beam cleaning and abort systems and other locations
of possible high beam loss. 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
toxic or hazardous, and which contain radioactive waste, is an important
concern.

##### C. Airborne Radioactivity {#c.-airborne-radioactivity .unnumbered}

Federal Regulations promulgated by the USEPA 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 \[[^108]5\]. 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 USEPA. Given the extent of the VLHC beyond the present boundaries of
the Fermilab site, careful attention must be paid to the production of
airborne radioactivity.

##### D. Radioactivity in Soil and Groundwater {#d.-radioactivity-in-soil-and-groundwater .unnumbered}

The VLHC siting requires that the production of radioactivity in
hydrogeologic units be given careful attention. 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.

#### 5.3.7.7. Non-Radiological Environmental Protection Issues During Operations  {#non-radiological-environmental-protection-issues-during-operations .unnumbered}

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. In
any enclosures located deep underground the cross-contamination of the
various aquifers must be prevented and any de-watering operations must
assure that local community or individual drinking water supplies are
not perturbed.

#### 5.3.7.8. Summary {#summary .unnumbered}

The construction and operation of the VLHC present a number of ES&H
challenges. 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 scale of the VLHC some of these issues may have a greater
importance than found in the present experience. 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 {#references .Reference-heading .unnumbered}

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

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[^2]: \[?\] E. Malamud, ed., "The Pipetron: a Low-Field Approach to a
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[^3]: \[?\] G.W. Foster, "Transmission Line Magnet Status Report," VLHC
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[^4]: \[?\] G.W. Foster, V.S. Kashikhin, E. Malamud, P. Mazur, H.
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[^5]: \[?\] Ron Walker, 50 m Invar Thermal Cycling Report.

[^6]: \[?\] Quench simulation final report, TD note #?

[^7]: \[?\] J. DiMarco, G.W. Foster, V. Kashikhin, A. Makarov, P.
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[^8]: \[?\] G.W. Foster, V.S. Kashikhin, I. Novitski, "Design of a 2
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[^9]: \[?\] G.W. Foster, V.S. Kashikhin, V.V. Kashikhin, "Pole Profile
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[^10]: \[?\] G.W. Foster, EPAC '98 talk and other Recycler shim talks.

[^11]: \[?\] Kashikhin write-up on corrector wires in
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[^12]: \[?\] V. Tsvetkov, "Transmission Line Magnet Mechanics," TD TN
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[^13]: \[?\] V. Tsvetkov, "Alignment of the Transmission Line Magnet in
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[^14]: \[?\] V.S. Kashikhin, "Mechanical model 2 test results," TD TN
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[^15]: \[?\] V.S. Kashikhin, "Transmission Line Magnet for VLHC.
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[^16]: \[?\] M. McAshan, "Cryogenic System for the 3 TeV Injector
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[^17]: \[?\] ULTEM 2300 is a 40% glass-filled polyetherimide marketed by
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[^18]: \[?\] G.W. Foster, "Mechanical Load Cycling Tests of the
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[^19]: \[?\] I. Novitski, "Analysis of the spider support," TD TN XXXX
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[^20]: \[?\] E.C. Quimby et al., "VJR/VJRR Design, Construction,
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[^21]: \[?\] G. Grygiel et al., "Status of the TTF Cryogenic System,"
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[^22]: \[?\] K. Hosoyama et al., "Development of a High Performance
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[^23]: \[?\] R. Walker et al., "Thermal Cycle Testing of Invar Pipe
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[^24]: \[?\] M. Chorowski, "Risk analysis of the LHC cryogenic system,"
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[^25]: \[?\] V. Parma et al., "The Insulation Vacuum Barrier for the
    Large Hadron Collider Magnet Cryostats," ICEC 18.

[^26]: \[?\] B. Jenny et al., "A Composite Vacuum Barrier for the LHC
    Short Straight Section," *ACE* vol.41, New York 1996.

[^27]: \[?\] "Technical Specification for a Compound Cryogenic Helium
    Distribution Line for the Large Hadron Collider (LHC),"
    IT-2399/lhc/lhc, Geneva, Switzerland, December 1997.

[^28]: \[?\] R.C. Niemann, "Model SSC Dipole Magnet Cryostat Assembly at
    Fermilab," Supercollider 1, New York 1989.

[^29]: \[?\] N. Andreev, TD Note.

[^30]: \[?\] G. Ambrosio et al., "Preliminary Proposal of a Nb~3~Sn
    Quadruple Model for the Low-Beta Insertions of the LHC," INFN
    Report, INFN/TC-95/25, Sept. 13, 1995.

[^31]: \[?\] R. Scanlan, "Conductor Development Program," Low
    Temperature Superconducting Workshop, Santa Rosa, CA, Nov. 8-10,
    2000.

[^32]: \[?\] M. Canali, L. Rossi, "DYNQUE: a computer code for quench
    simulation in adiabatic multicoil superconducting solenoids," INFN
    Report, INFN/TC-93/06, 1993.

[^33]: \[?\] 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).

[^34]: \[?\] G. Ambrosio, G. Bellomo and L. Rossi, "A 300 T/m Nb~3~Sn
    Quadrupole for the Low-beta Insertions of the LHC," *Proc. of
    EPAC96*, Sitges (Barcelona), p. 2290.

[^35]: \[?\] Nikolai Mokhov, private communication.

[^36]: \[?\] Bill Turner, private communication.

[^37]: \[?\] V.V. Kashikhin, I. Terechkine, "Superconducting straight
    section quadrupole magnet for low-field VLHC," FNAL, TD-01-008, Feb.
    2001.

[^38]: \[?\] Conceptual Design of the Superconducting Super Collider.
    SSC-SR-2020, DE93 007234.

[^39]: \[?\] J. Volk, "Injection transfer line magnets," TD Note
    TD-01-027, FNAL, 2001.

[^40]: \[?\] J. Carson, R. Bossert, "A Proposed Production Procedure for
    Stage 1 Transmission Line Magnets," TD-01-028, 2001.

[^41]: \[?\] J. Carson, R. Bossert, "Throughput for Stage 1 Transmission
    Line Factory," TD-01-029, 2001.

[^42]: One unit of harmonic corresponds to 10^-4^ of the main field,
    measured at a reference radius (in our case) of 1cm.

[^43]: Calibration in both a dipole and quadrupole magnet are required
    due to the large gradient which we want to measure with high
    accuracy.

[^44]: \[?\] P. Schlabach, "Magnetic Measurements During Production of
    VLHC Low Field Combined Function Magnets," TD-01-007, 2001.

[^45]: \[?\] G. Ganetis et al., "Field Measuring Probe for SSC Magnets,"
    Particle Accelerator Conference, 1987.

[^46]: \[?\] L. Walkiers, "Measurements for the Acceptance Tests of the
    LHC Superconducting Magnets," Eleventh International Magnet
    Measurement Workshop, 1999.

[^47]: \[?\] Brown & Root, Installation & Transport Proposal for the
    SSC.

[^48]: \[?\] Supply of Cryo-Magnet Transport Vehicles and Unloading
    Equipment for the LHC Tunnel, LHC-HMU-CI-0001 (from the CERN LHC Web
    site, which no longer has useful static links).

[^49]: \[?\] An example of a commercial safety rail can be found at
    <http://www.vahleinc.com/pdf/Catalog4C.pdf>.

[^50]: \[?\] 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>.

[^51]: \[?\] Who?, PAC 2001 invited talk.

[^52]: \[?\] Steve Hays, "100 kA Power Supply Options for the VLHC,"
    internal note (unpublished).

[^53]: \[?\] H. Piekarz et al., "Summary of Transmission Line Magnet R&D
    Activities at MS-6," VLHC Note NNNN.

[^54]: \[?\] G.W. Foster, S. Hays, H. Pfeffer, "Design of a Compact
    100 kA Switching Power Supply for Superconducting Magnet Tests,"
    VLHC Note NNN.

[^55]: \[?\] J. G. Weisand (ed.), *Handbook of Cryogenic Engineering*,
    p. 411.

[^56]: \[?\] K. Koepke, P. Mazur, A. Zlobin, Snowmass '96.

[^57]: \[?\] G.W. Foster, H. Piekarz, "Quench Protection of the
    Transmission Line Magnet," VLHC note (unpublished).

[^58]: \[?\] Switch wire is used on persistent-current MRI magnets.
    Commercial sources include SW-18 and SW-1 from Supercon Inc,
    Shrewsbury, MA, and Oxford Instruments, www.oxinst.com.

[^59]: \[?\] 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.](http://lhcp.web.cern.ch/lhcp/TCC/PLANNING/TCC/Power2000/welcome.htm)

[^60]: \[?\] I. Terechkine, "LCW and power summary for the VLHC-1
    Straight Sections," VLHC Note NNN.

[^61]: \[?\] Fermilab Main Injector Technical Design Report, Table
    3.9.1.

[^62]: \[?\] Typical laptop computers have heat pipes in them. See
    <http://www.thermacore.com/papers.htm>.

[^63]: \[?\] Auto-resetting fuses are sold (for example) by:
    [http://www.circuitprotection.com](http://www.circuitprotection.com/).

[^64]: \[?\] Specifications quoted are single-quadrant DC-DC converters
    from Vicor, Inc. [www.vicor.com](../www.Vicr.com).

[^65]: \[?\] Fermilab Main Injector Note MI-75.

[^66]: \[?\] Medvenko & Smith, Beam Instrumentation Workshop 2000,
    p.503.

[^67]: \[?\] Specifications quoted are from
    <http://products.analog.com/products/info.asp?product=AD9203>.

[^68]: \[?\] 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.

[^69]: \[?\] M. Pivi and W.C. Turner, "Beam Tube Vacuum in a Very Large
    Hadron Collider Stage 1," Version 2.1, 12 April 2001.

[^70]: \[?\] 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.

[^71]: \[?\] C. Benvenuti, "Molecular Surface pumping: the getter
    pumps," CAS CERN Accelerator School - Vacuum Technology, CERN Yellow
    Book, pg. 48.

[^72]: \[?\] 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.

[^73]: \[?\] G.P. Jackson, ed., "The Fermilab Recycler Technical Design
    Report", FNAL-TM-1991.

[^74]: \[?\] I. Novitski, VLHC note on vacuum pipe stresses.

[^75]: \[?\] A. Chao and M. Tigner*, Handbook of Accelerator Physics and
    Engineering,* pg.225.

[^76]: \[?\] Oswald Gröbner pvt. comm.

[^77]: \[?\] 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.

[^78]: \[?\] Bob Goodwin, Peter Lucas, Elliott McCrory and Mike Shea,
    "Thoughts on Controls/Instrumentation for 3 TeV booster/VLHC,"
    <http://fnalpubs.fnal.gov/archive/vlhc/VLHCPub-14.html>, July 1997.

[^79]: \[?\] 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>.

[^80]: \[?\] A. Jackson, contribution to the VLHC Design Study,
    unpublished.

[^81]: \[?\] The LHC Study Group, "The Large Hadron Collider --
    Conceptual Design Report," CERN/AC/95-05 (LHC) (1995).

[^82]: \[?\] 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.

[^83]: \[?\] 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.

[^84]: \[?\] 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.

[^85]: \[?\] D. Boussard, "RF Power Requirements for a High Intensity
    Proton Collider," *Proceedings of the 1991 Particle Accelerator
    Conference,* pp. 2447-2449.

[^86]: \[?\] 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.

[^87]: \[?\] H. Padamsee, "SRF for Muon Colliders," *Proceedings of the
    9th Workshop on RF Superconductivity,* 1-5 November 1999, Santa Fe,
    NM, USA.

[^88]: \[?\] G. Lambertson, final report for VLHC design study (TD Note
    xxx).

[^89]: \[?\] N.V. Mokhov and W. Chou, ed., "Beam Halo and Scraping,"
    *Proc. of ICFA Workshop*, Lake Como, Wisconsin (1999).

[^90]: \[?\] Bryant & Johnsen, *Circular Accelerators and Storage
    Rings*, p. 308.

[^91]: \[?\] 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.

[^92]: \[?\] 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>.

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

[^94]: \[?\] *The Large Hadron Collider*, Conceptual Design,
    CERN/AC/95-05(LHC) October 20, 1995.

[^95]: \[?\] 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.

[^96]: \[?\] N. Mokhov, pvt. comm.

[^97]: \[?\] R. Yarema, pvt. comm.

[^98]: \[?\] LHC Talk at Beam Instrumentation Workshop '00.

[^99]: \[?\] 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.

[^100]: \[?\] A.I. Drozhdin and N.V. Mokhov, "The VLHC Beam Collimation
    System," VLHC design study note.

[^101]: \[?\] 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.

[^102]: \[?\] 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).

[^103]: \[?\] Electron Beam Tunnel Boring papers from LBL, circa 1975.

[^104]: \[?\] "Fermilab Work Smart Standards Set," Fermi National
    Accelerator Laboratory,
    http://www-lib.fnal.gov/library/protect/worksmart.html, November 15,
    1999.

[^105]: \[?\] *United States Code of Federal Regulations, Title 10, Part
    1021*, "{Department of Energy} National Environmental Policy Act
    Implementation Procedures," 1997.

[^106]: \[?\] A. Van Ginneken, P. Yurista, and C. Yamaguchi, "Shielding
    calculations for multi-TeV hadron colliders," Fermilab Report FN-447
    (1987).

[^107]: \[?\] U. S. Department of Energy, "Radiation Protection of the
    Public and the Environment," DOE Order 5400.5, January 7, 1993.

[^108]: \[?\] *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.