8.  **Magnet Installation**

More than three thousand 65 m superferric magnets and their associated
subsystems must be installed in the arcs of the 240-km accelerator ring.
This installation must be tightly coordinated with tunnel excavation,
outfitting, and magnet manufacturing. The scale of this work and the
difficulty of subsequent maintenance require techniques that ensure high
quality installation resulting in high reliability of the accelerator.

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

The baseline assumptions adopted for the arc magnet installations are:

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

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

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

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

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

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

A basic constraint on the installation is that it be consistent with the
addition of the Stage 2 magnets at a later time.

Because at the second stage High Field Ring will modify tunnel layout,
while planning all of the mentioned above works, we must consider this
future collider upgrade so that installed equipment wouldn\'t make this
upgrade too complicated. Tunnel cross section with both Low Field and
High Field accelerators installed is shown in Fig. 1.

![](media/image1.wmf){width="2.716666666666667in"
height="2.7131944444444445in"}

*Figure 1. Tunnel cross-section after the stage-2 upgrade.*

#### 5.1.8.1 Tunnel Infrastruture Installation

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

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

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

The time at which electronics modules are installed and comissioned 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 envronmental monitoring they should be installed
earlier. An early installation date encourages earlier system debugging,
but a design that is frozen several years before project completion will
be painfully obsolete by the time of commissioning.

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

#### 5.1.8.2 Tunnel Transportation System

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

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

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

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

#### 5.1.8.3 Magnet Handling and Transportation Considerations

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

Allowable limits on static deformation and torsion of the magnet are
shown in Table 1. In the three cases in the table, a force (or force
couple) was applied it to a single set of magnet support/adjusters while
the magnet cross section was held fixed +/-6m away at the position of
the adjacent magnet supports.

## Table 1. Limits of relative displacement of magnet parts over +/-6m length

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

The magnet structure is quite flexible taking into account its length.
Just due to its own weight, vertical sag can exceed the limits from the
table 1 if one of the supports is removed. On the other hand, a smooth
continuous bend with 1km radius of curvature produces a 50cm sagitta in
the magnet with acceptable internal stresses. To significantly reduce a
risk of magnet damage during transportation, a 60m long aluminum frame
is used at this stage. The frame increases assembly rigidity and
preserves magnet from the vertical bending damage. Fig. 2 shows the
frame moving inside the tunnel. Fig 3 shows the "A-Frame" structure of
the beam which permits it to be lifted or driven off of the magnet.

![](media/image2.wmf){width="6.189583333333333in"
height="0.5770833333333333in"}*Figure 2. Magnet transportation frame,
which acts as a "lifting fixture" to uniformly support the magnet and
prevent stress concentrations during transport and installation.*

During transportation, dynamic loading effects have the potential to
increase stress levels in the magnet. During transportation and
installation, it is necessary to monitor and correct relative
displacement of magnet parts to the limits well below those of table 1.
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 vehicles on both sides of the frame, each with engine
power of 60 kW and a typical operating power of 15kW, pull the frame
during transportation from production facility to the designated
location in the tunnel. An alternative chosen by the SSC & LHC is to use
a general-purpose towing tractor pulling a passive magnet trailer.

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

#### 5.1.8.4 Initial Magnet Installation

The installation scheme shown in Fig 3 corresponds to the simplest case
when magnet installation occurs with a clear space upstream or
downstream of the installation point.

![](media/image3.wmf){width="5.988888888888889in"
height="1.3611111111111112in"}*Figure 3 - Initial installation scheme
which is possible when the upstream or downstream magnet slot is empty.
Installation vehicle a) drives up to the location along the beam line,
b) deposits the magnet on the pre-aligned stands, and c-d) departs by
initially moving along the beam line, then moving if needed to the
center lane to pass any pre-installed magnets. Final connections e) may
be made by separate work work crews working off-shift or in different
sections of the tunnel.*

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

Magnets are driven to their location along the beam line and put on the
support blocks without any transverse movement (Fig, 3 b). Unloaded
frames are then backed out along th installation pathway (Fig, 3 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

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

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

-   splicing of superconducting cables;

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

-   connection of cryogenic piping;

-   installation of a 50 K screen and superinsulation;

-   sealing and leak checking the insulating vacuum

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

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

#### 5.1.8.6 Corrector Magnet Skid

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

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

#### 5.1.8.7 Magnet Replacement

A more complicated mechanical situation arises in the (hopefully rare)
situation that a magnet needs to be replaced after installation, or is
installed as the last magnet an otherwise complete arc. In this case the
magnet will be transported parallel to the magnets that have already
been installed (Fig. 4 a; installed magnets are not shown). Using
hydraulic and control systems on transportation trailers, the magnet
will be lowered down to temporary support stands installed beneath the
carts (Fig. 4 b). After the frame is removed (Fig. 4 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 (Fig. 4 d, e). Control equipment similar to
used during transportation will synchronize the system during this
operation. This procedure will also be used to replace a Stage 1 magnet
after Stage 2 installation is complete.

![](media/image4.wmf){width="5.988888888888889in"
height="1.4722222222222223in"}*Figure 4. Magnet replacement scheme.*

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

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

-   open the connection space;

-   remove super-insulation;

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

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

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

-   make interconnections as described above;

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

#### 5.1.8.8 Arc Magnet Alignment

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

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

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

**Vertical alignment** can be made using a hydrostatic leveling
technique, that make 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 Earth gravitation field must be made. This will
require careful study of the Geoid and the change in the density of the
earth in the region of the machine. Corrections to the vertical can then
be imposed on each magnet.

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

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

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

#### 5.1.8.9 Straight Sections and Transfer Line Installation

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

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

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

Finally there are eight 10-meter, superconducting, high gradient,
low-beta IR quadrupoles described in 5.1.4. Each quadrupoles will weigh
about 25 ton and is rigid enough to be transported to the place of
installation using two high load trailers and two transport vehicles of
the type used for the arc magnet transportation. The alignment
requirement for these quadrupoles installation is 100 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\'s arcs, installation of
these magnet can be done independently of the installation of arc
magnets.

#### 5.1.8.10 Installation Schedule

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

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

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

#### 5.1.8.11 System Commissioning

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

A temporary installation of the 100kA holding supply and current leads
(fig. 5.42) easily fits in the underground caverns eventually intended
for the Stage 2 dump resistors. The 2.5V holding supply will ramp a 20km
magnet string to 100kA in 40 minutes. This allows full-current testing a
complete quench protection cell of the accelerator.

Beam pipe is interconnected after the cryo-test shows an acceptable
magnet string quality and correction magnet block is installed. Because
the system is not baked *in situ*, the static vacuum will improve
steadily over time and it is desirable to have most of the system under
vacuum for as long as possible before storage ring comissioning.

References

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

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

> \[3\] An example of a commercial safety rail can be found at
> <http://www.vahleinc.com/pdf/Catalog4C.pdf>
>
> \[4\] Examples of tram systems and drive components operating in this
> voltage range can be found at
> <http://w4.siemens.de/ts/products_solutions/light_rail_tram>
>
> \[5\] PAC 2001 invited talk.