## LHC Interaction Region Quadrupole Cryostat

December 3, 1998

Thomas H. Nicol

Fermi National Accelerator Laboratory

P.O. Box 500

Batavia, IL 60510

USA

##### ABSTRACT

The cryostat of a superconducting dipole magnet consists of all magnet
components except the magnet assembly itself. It serves to support the
magnet accurately and reliably within the vacuum vessel, provide all
required cryogenic piping, and to insulate the cold mass from heat
radiated and conducted from the environment. It must function reliably
during storage, shipping and handling, normal magnet operation,
quenches, and seismic excitations, and must be able to be manufactured
at low cost.

The major components of the cryostat are the vacuum vessel, thermal
shields, multi-layer insulation system, cryogenic piping,
interconnections, and suspension system. The overall design of a
cryostat for superconducting accelerator magnets requires consideration
of fluid flow, proper selection of materials for their thermal and
structural performance at both ambient and operating temperature. In
addition, consideration must be given to the operating environment in
which the magnets must function over the course of their expected
operating life.

This paper describes the current state of the design for LHC interaction
region quadrupole (IRQ) cryostats and includes discussions on the
structural and thermal considerations involved in the development of
each of the major systems.

##### INTRODUCTION

Cryostat designs for superconducting magnets are largely driven by
thermal and structural considerations. Designers must continually be
cognizant of the heat load to the helium system and of the structural
loads imposed on the cryostat systems from static weight, shipping and
handling, quench loads, and ambient ground motion. These two
considerations are generally at odds with one another. Low heat load
implies a minimum of structural material conducting heat from the
environment. Sound structural design implies material with sufficient
strength to resist both static and dynamic forces.

![](media/image2.wmf){width="6.122916666666667in"
height="3.7305555555555556in"}

Figure 1. LHC IRQ Cryostat Cross Section

This paper attempts to summarize the results of the design effort to
date on the LHC interaction region quadrupole cryostats. Thermal and
structural aspects of the design of each of the major cryostat systems
will be described in detail. Each of the cryostat systems will be
addressed in turn; vacuum vessel, thermal radiation shield, multi-layer
insulation (MLI), cryogenic piping, suspension system, and magnet
interconnect.

In order to begin the design process, one needs a good handle on the
pertinent allowable heat loads to each thermal station as well as a good
definition of the structural environment to which the magnet will be
subjected. Tables 1 through 3 summarize the thermal and structural
design criteria affecting the design of the IRQ cryostats. Table 4
simply documents what we know about alignment criteria at this time.

  ---------------------------- -------------- -------------- --------------
  **Table 1. Thermal design                                  
  criteria**                                                 

  **Temperature**              **50 to 70K**  **4.5 to 20K** **1.9K**

  Static heat load (W)         170            20             40

  Dynamic heat load            0              0              150

  Total                        **170**        **20**         **190**
  ---------------------------- -------------- -------------- --------------

\*: Heat loads are per triplet

  -------------------- -------------- ---------- ---------- ------------ ------------ -------------
  **Table 2.                                                                          
  Structural weights**                                                                

  **Magnet             **Length\***   **OD**     **ID**     **volume**   **weight**   **wt/supt**
  Designation**                                                                       

  **(Manufacturer)**   **(m)**        **(mm)**   **(mm)**   **(m3)**     **(lb)**     **(lb)**

  Q1, Q3 (KEK)         6.604          500        70         1.271        22187        11094

  Q1, Q3 (Fermilab)    6.604          416        70         0.872        15222        7611

  Q2a, Q2b (KEK)       5.804          500        70         1.117        19500        9750

  Q2a, Q2b (Fermilab)  5.804          416        70         0.767        13378        6689
  -------------------- -------------- ---------- ---------- ------------ ------------ -------------

\*: End plate to end plate dimension.

+------------------------------------------------+---------------------+
| **Table 3. Shipping and handling loads**       |                     |
+------------------------------------------------+---------------------+
| ### Direction                                  | **Load**            |
+------------------------------------------------+---------------------+
| Lateral                                        | 1 g                 |
+------------------------------------------------+---------------------+
| Vertical (weight + 1 g)                        | 2 g                 |
+------------------------------------------------+---------------------+
| Axial (with shipping restraint)                | 0.1 g               |
+------------------------------------------------+---------------------+

+------------------------------------------------+---------------------+
| **Table 4. Alignment criteria**                |                     |
+------------------------------------------------+---------------------+
| ### Position                                   | **Criteria**        |
+------------------------------------------------+---------------------+
| Precision of the cold mass with respect to the | 100 microns         |
| external fiducials                             |                     |
+------------------------------------------------+---------------------+

##### COLD MASS OPTIONS

In addition to summarizing the structural requirements, Table 2
illustrates the various cryostat options that must be considered in the
design development. Fermilab and KEK are both producing cold masses with
diameters of 416 and 500 mm respectively. Also, there are at least two
different cold mass lengths in a complete triplet. We would like to use
as many common parts as possible in all the designs. For that reason,
the piping, shields, multi-layer insulation, supports, bellows, etc.
will be as much alike as possible. Piping lengths of course will vary as
necessary, but structures like the supports will be identical. The
structural loads are therefore dictated by the Q1 and Q3 cold masses
from KEK.

##### VACUUM VESSEL

The vacuum vessel is the outermost cryostat component and, as such,
serves to contain the insulating vacuum. In addition, it functions as
the major structural element to which all other systems are ultimately
attached to the accelerator tunnel floor. Furthermore, it serves as a
pressure containment vessel in the event of a failure in an internal
cryogen line. The vessel is 914 mm OD, 12 mm wall. This is the same size
vessel planned for use in the main LHC dipoles. We are opting to use the
same size for two reasons. First it ensures the final assemblies will
fit in the available access tunnels and shafts. Second it may allow us
to use the same vendor and material as a cost saving measure. The length
of the individual vessels will be determined as the details of the
interconnect are finalized.

##### THERMAL RADIATION SHIELDS

The IRQ cryostats have a single shield cooled by helium gas at between
50K and 70K. The shields intercept heat radiated from the 300K surface
of the vacuum vessel and conducted through the support system. Two
aluminum extrusions serve as the supply and return for the shield flow.
The shield itself is a formed shell attached to the cryostat at the
support structure. The nature of the shield function requires that the
shell have high thermal conductivity to minimize thermal gradients
around their circumference. Copper and aluminum are the materials of
choice for this application. Thermal analyses were performed using both
materials. The results from these analyses indicate there is no
significant difference in the thermal performance of the shield between
these two materials. Cost dictated the ultimate material choice. Copper
and aluminum are approximately the same cost per unit weight, however,
with a density over three times that of aluminum, the use of copper as
the shield material would result in an assembly cost three times higher
than an aluminum shield. The selected material is 6061-T6 aluminum,
3.175 mm thick. The shields are segmented along their length to minimize
the effect of thermally induced distortions during cooldown caused by
the asymmetry cooling of the supply and return tubes.

In addition to the 50 to 70K shield shell, two 4.5K tubes pass through
the cryostat and serve as heat intercepts for the beam absorbers.

##### MULTI-LAYER INSULATION

The multi-layer insulation system will be modeled after the 80K shield
insulation in SSC magnets. That system consisted of two
32-reflective-layer blanket assemblies, for a total of 64 reflective
layers. The stack height of each 32-layer blanket is 8.86 mm, with a
mean layer density of 3.61 layers per mm. The blanket design
incorporates 32 reflective layers of double-aluminized polyethylene
terepthalate (PET) film. The reflective layers consist of flat polyester
film aluminized on both sides to a nominal thickness not less than 350
angstroms. The spacer layers consist of randomly oriented spunbonded
polyester fiber mats. The mean apparent thermal conductivity of an MLI
blanket comprised of these materials has been measured to be 0.52 x10-6
W/cm-K.

##### CRYOGENIC PIPING

In addition to providing the necessary structural support and thermal
insulation for the cold mass assembly, the cryostat serves to contain
the piping for all of the cryogenic services required for magnet and
magnet system operation. Table 2 provides a summary of the pressure and
flow parameters for each of these services. Table 3 lists the pipe sizes
for each of the cryostat pipes. The shield extrusions are anchored at
one of the magnet supports and are free to slide axially at the other to
allow for thermal contraction. All of the 1.8K pipes are attached to
supports that are in turn attached to the cold mass. This scheme
minimizes the heat load to the structural supports. These pipes are also
axially anchored at only one point. Table 5 summarizes the size of all
the cryostat pipes. Table 6 lists the flow required design pressures,
temperatures and flows.

+---------------+-----+-----+-----+-----+-----+-----+---------------+
| #### Ta       |     |     |     |     |     |     |               |
| ble 5. Cryost |     |     |     |     |     |     |               |
| at pipe sizes |     |     |     |     |     |     |               |
+---------------+-----+-----+-----+-----+-----+-----+---------------+
| **            | **O | **I | **  | **O | **I | **  | #### Notes    |
| Description** | D** | D** | Tkn | D** | D** | Tkn |               |
|               |     |     | s** |     |     | s** |               |
|               | **  | **  |     | **  | **  |     |               |
|               | (mm | (mm | **  | (in | (in | **  |               |
|               | )** | )** | (mm | )** | )** | (in |               |
|               |     |     | )** |     |     | )** |               |
+---------------+-----+-----+-----+-----+-----+-----+---------------+
| Vacuum vessel | 91  | 89  | 1   | 35. | 35. | 0.  | Carbon steel  |
|               | 4.0 | 0.0 | 2.0 | 984 | 039 | 472 |               |
+---------------+-----+-----+-----+-----+-----+-----+---------------+
| Pumping line  | 88. | 85. | 1.  | 3.  | 3.  | 0.  |               |
|               | 900 | 598 | 651 | 500 | 370 | 065 |               |
+---------------+-----+-----+-----+-----+-----+-----+---------------+
| External heat | 1   | 1   | 2.  | 6.  | 6.  | 0.  |               |
| exchanger     | 68. | 62. | 769 | 625 | 407 | 109 |               |
| outer shell   | 275 | 738 |     |     |     |     |               |
+---------------+-----+-----+-----+-----+-----+-----+---------------+
| External heat | 97. | 96. | 0.  | 3.  | 3.  | 0.  | Copper        |
| exchanger     | 536 | 012 | 762 | 840 | 780 | 030 | corrugation   |
| inner tube    |     |     |     |     |     |     | (approximate  |
|               |     |     |     |     |     |     | dimensions)   |
+---------------+-----+-----+-----+-----+-----+-----+---------------+
| Cooldown line | 44. | 41. | 1.  | 1.  | 1.  | 0.  |               |
|               | 450 | 961 | 245 | 750 | 652 | 049 |               |
+---------------+-----+-----+-----+-----+-----+-----+---------------+
| LHe supply    | 15. | 13. | 1.  | 0.  | 0.  | 0.  |               |
|               | 875 | 386 | 245 | 625 | 527 | 049 |               |
+---------------+-----+-----+-----+-----+-----+-----+---------------+
| 4.5K supply   | 15. | 13. | 1.  | 0.  | 0.  | 0.  |               |
|               | 875 | 386 | 245 | 625 | 527 | 049 |               |
+---------------+-----+-----+-----+-----+-----+-----+---------------+
| 4.5K return   | 15. | 13. | 1.  | 0.  | 0.  | 0.  |               |
|               | 875 | 386 | 245 | 625 | 527 | 049 |               |
+---------------+-----+-----+-----+-----+-----+-----+---------------+
| 50-70K shield | 83  | 8   | 3.  | 32. | 32. | 0.  | Aluminum      |
| shell         | 0.0 | 23. | 175 | 677 | 427 | 125 | shell         |
|               |     | 650 |     |     |     |     |               |
+---------------+-----+-----+-----+-----+-----+-----+---------------+
| 50-70K shield | 76. | 69. | 3.  | 3.0 | 2.  | 0.  | Aluminum      |
| supply        | 200 | 850 | 175 |     | 750 | 125 | extrusion     |
+---------------+-----+-----+-----+-----+-----+-----+---------------+
| 50-70K shield | 76. | 69. | 3.  | 3.0 | 2.  | 0.  | Aluminum      |
| return        | 200 | 850 | 175 |     | 750 | 125 | extrusion     |
+---------------+-----+-----+-----+-----+-----+-----+---------------+
| KEK cold mass | 50  | 47  | 1   | 19. | 18. | 0.  | ID is         |
|               | 0.0 | 0.0 | 5.0 | 685 | 504 | 591 | estimated     |
+---------------+-----+-----+-----+-----+-----+-----+---------------+
| Fermilab cold | 41  | 40  | 8.0 | 16. | 15. | 0.  | ID is         |
| mass          | 6.0 | 0.0 |     | 378 | 748 | 315 | estimated     |
+---------------+-----+-----+-----+-----+-----+-----+---------------+
| Stiffener     | 95  | 102 | na  | 37. | 40. | na  | OD is width,  |
|               | 0.0 | 5.0 |     | 402 | 354 |     | ID is height  |
+---------------+-----+-----+-----+-----+-----+-----+---------------+

+-----------------+---------+---------+---------+---------+---------+
| ### Table 6. C  |         |         |         |         |         |
| ryostat piping  |         |         |         |         |         |
| flow parameters |         |         |         |         |         |
+-----------------+---------+---------+---------+---------+---------+
| ### Description | **      | **P     | **P     | **T**   | *       |
|                 | Fluid** | oper**  | max**   |         | *Flow** |
|                 |         |         |         | **(ap   |         |
|                 |         | **      | **      | prox)** | **      |
|                 |         | (atm)** | (atm)** |         | (g/s)** |
+-----------------+---------+---------+---------+---------+---------+
| Pumping line    | Ghe     | 0.016   | 4.0     | 1.8 K   | 8.6     |
+-----------------+---------+---------+---------+---------+---------+
| External heat   | Lhe     | 3.6     | 20.0    | 1.9 K   | 0.0     |
| exchanger outer |         |         |         |         |         |
| shell           |         |         |         |         |         |
+-----------------+---------+---------+---------+---------+---------+
| External heat   | Lhe     | 0.016   | 4.0     | 1.8 K   | 8.6     |
| exchanger inner |         |         |         |         |         |
| tube            |         |         |         |         |         |
+-----------------+---------+---------+---------+---------+---------+
| Cooldown line   | Lhe     | 3.6     | 20.0    | 1.9 K   | 30.0    |
+-----------------+---------+---------+---------+---------+---------+
| LHe supply      | Lhe     | 0.016   | 4.0     | 1.8 K   | 8.6     |
+-----------------+---------+---------+---------+---------+---------+
| 4.5K supply     | Lhe     | 1.3     | 20.0    | 4.5 K   | 1.1     |
+-----------------+---------+---------+---------+---------+---------+
| 4.5K return     | Lhe     | 1.3     | 20.0    | 4.5 K   | 1.1     |
+-----------------+---------+---------+---------+---------+---------+
| 50-70K shield   | Ghe     | 19.5    | 22.0    | 60 K    | 5.0     |
| supply          |         |         |         |         |         |
+-----------------+---------+---------+---------+---------+---------+
| 50-70K shield   | GHe     | 19.0    | 22.0    | 65 K    | 5.0     |
| return          |         |         |         |         |         |
+-----------------+---------+---------+---------+---------+---------+

##### COLD MASS

Ordinarily, the design of the cold mass has little bearing on the design
of the cryostat. For these magnet assemblies however, the cryostat
designers will assume responsibility for the end closure and
interconnecting cold mass piping. We will need to define the magnet
interfaces to ensure that cold masses produced by Fermilab and KEK are
identical in overall length including end closures and that there is a
well defined connection between the cold mass and support system for all
magnets.

##### SUSPENSION SYSTEM

The suspension system in any superconducting magnet serves as the
structural attachment for all cryostat systems to the vacuum vessel that
in turn anchors them to the accelerator tunnel floor. The emphasis was
on meeting the allowed suspension system conduction heat load from Table
1, satisfying the structural requirements in Tables 2 and 3, and
maximizing the suspension stiffness. This latter constraint is not
explicitly defined in the design criteria, but comes from experience
testing similar magnets that assemblies that are more rigid tend to be
more structurally stable during shipping and handling.

The first suspension system conceptual design utilized a single support
post similar to those developed for SSC dipole cryostats. The
development of the post-type support system was driven by the need for
low heat loads to the magnet system. It suffers from two things. First
it is laterally very flexible which makes precise positioning difficult.
Second, posts occupy a lot of radial space. This second problem almost
precludes the use of a single post for the IRQ cryostat. There just
isn't sufficient space for such a support , the cold mass, and the
external heat exchanger.

It is possible to use two posts arranged in a truss-like configuration
with the external heat exchanger between the two. This arrangement has
several advantages over a single support. First it maintains the low
heat load properties of a single support. It provides for a much greater
lateral stiffness than a single support. And finally, it naturally makes
radial space available for things like the external heat exchanger.
Assembly however becomes difficult because this design is not easily
integrated into conventional assembly schemes.

The current conceptual design for the IRQ cryostat suspension system
uses a different approach. Since low heat load is not a strong design
constraint due to the high beam induced heating we are looking into the
performance of a composite "spider" support. Such a support provides
high strength and stiffness, integrates well with the piping and thermal
shield, and is reasonably thermally efficient. In addition it affords
one design feature not easily realized with other supports. It minimizes
movement of the cold mass centerline during cooldown. This is not a
published design constraint, but might be a nice operational feature.
Figure 1 illustrates a conceptual cross section that utilizes this
support. Figure 2 illustrates the support itself.

![](media/image3.wmf){width="6.122916666666667in" height="3.85625in"}

Figure 2. LHC IRQ Cryostat Spider Support

##### INTERCONNECT

As its name implies the magnet interconnect serves as the area between
magnets at which each of the cold mass and cryostat pipes between
magnets are connected. Each pipe is anchored axially near one end of the
magnet assembly which means they contract between approximately 22 mm
and 30 mm depending on whether they are stainless steel or aluminum.
Bellows are required on each cold mass, shield, and cryogenic pipe to
allow for this expansion. All bellows are hydroformed stainless steel.
For the aluminum extrusions on the shield aluminum to stainless steel
transition joints are required for the bellows connection. Lateral
instability is a concern for interconnect bellows and requires the use
of internal squirm protectors on each bellows assembly.

Radiative heat transfer must also be minimized in the interconnect area.
Shield bridges that span the gap between adjacent magnets accomplish
this. These bridges are extensions of the magnet shields, modified to
contain their respective bellow OD\'s if necessary. A sliding joint
between bridge sections on adjacent magnets accommodates contraction
during cooldown. Each is covered with the same MLI scheme used
throughout the body of the magnet. Each shield bridge also has a
pressure relief to prevent pressure buildup in the event of an internal
piping failure. They are located in the upper half of the shield
sections in order to prevent liquid spills from impinging directly onto
the vacuum vessel wall.

One of the things that makes LHC IRQ cryostats interesting is the
variety of other components which are located in the interconnect areas
in addition to the normal pipe connections, shield bridges, electrical
connections, and instrumentation. At this time there are two different
correction coil, two different size beam absorbers, and two beam
position monitors (BPM) located along the length of each triplet. Table
7 lists what is currently known about each of these components. Figure 3
illustrates a layout of the triplet from the latest version of beam
optics and shows the position of the interconnect components.

+---------+---------+--------+--------+--------+-----------------------+
| #### Ta |         |        |        |        |                       |
| ble 7.  |         |        |        |        |                       |
| Interco |         |        |        |        |                       |
| nnect c |         |        |        |        |                       |
| omponen |         |        |        |        |                       |
| t posit |         |        |        |        |                       |
| ions an |         |        |        |        |                       |
| d physi |         |        |        |        |                       |
| cal par |         |        |        |        |                       |
| ameters |         |        |        |        |                       |
+---------+---------+--------+--------+--------+-----------------------+
| **P     | ######  | **OD** | **ID** | **Le   | **Notes**             |
| osition |  Device |        |        | ngth** |                       |
| along   |         | **     | **     |        |                       |
| tr      | *       | (mm)** | (mm)** | **     |                       |
| iplet** | *name** |        |        | (mm)** |                       |
+---------+---------+--------+--------+--------+-----------------------+
| End of  | MCBX    | 350    | 90     | 556    | [http                 |
| Q3      |         |        |        |        | ://roxa33.cern.ch](ht |
|         | co      |        |        |        | tp://roxa33.cern.ch/) |
|         | rrector |        |        |        | then to "ICP          |
|         |         |        |        |        | correctors" (see      |
|         |         |        |        |        | note)                 |
+---------+---------+--------+--------+--------+-----------------------+
| Q3/Q2b  | MCQS    | TBD    | TBD    | TBD    | [http                 |
|         |         |        |        |        | ://roxa33.cern.ch](ht |
|         | co      |        |        |        | tp://roxa33.cern.ch/) |
|         | rrector |        |        |        | then to "ICP          |
|         |         |        |        |        | Correctors" (not      |
|         |         |        |        |        | listed)               |
+---------+---------+--------+--------+--------+-----------------------+
| Q3/Q2b  | TAS 3   | 130 to | 70     | 1430   | Copper or steel per   |
|         |         | 190    |        |        | N. Mokhov             |
+---------+---------+--------+--------+--------+-----------------------+
| Q3/Q2b  | BPM     | 100    | 70     | 250    | Per R. Ostojic, Aug   |
|         |         |        |        |        | 23, 1998              |
+---------+---------+--------+--------+--------+-----------------------+
| Q2a/Q2b | MCBX    | 350    | 90     | 556    | [http                 |
|         |         |        |        |        | ://roxa33.cern.ch](ht |
|         | co      |        |        |        | tp://roxa33.cern.ch/) |
|         | rrector |        |        |        | then to "ICP          |
|         |         |        |        |        | Correctors"           |
+---------+---------+--------+--------+--------+-----------------------+
| Q2a/Q1  | TAS 2   | 130 to | 70     | 1380   | Copper or steel per   |
|         |         | 190    |        |        | N. Mokhov             |
+---------+---------+--------+--------+--------+-----------------------+
| End of  | BPM     | 100    | 70     | 250    | Per R. Ostojic, Aug   |
| Q1      |         |        |        |        | 23, 1998              |
+---------+---------+--------+--------+--------+-----------------------+

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![](media/image4.wmf){width="6.122916666666667in"
height="2.6666666666666665in"}Figure 3. LHC IRQ Cryostat Optics Layout

##### INTERFACE SUMMARY

Table 8 summarizes the known interfaces between the interaction region
quadrupole cryostats and other IR components, the parties responsible
for their definition, the current status, and an estimate of the
required completion date.

  ------------------- ------------------- ------------------- ------------
  **Table 8. Cryostat                                         
  Interface Milestone                                         
  Summary**                                                   

  **Interface or      **Responsible       **Current status**  **Required
  configuration       organization /                          completion
  description**       person(s)**                             date**

  Cryostat to MTF     Fermilab / T.       Feedbox preliminary Mar 1, 1999
  feedbox.            Nicol, T. Peterson, design complete.    
                      C. Reid                                 

  Cryostat to DFBX.   Fermilab and        Unknown.            Jul 1, 1999
                      Berkeley / T.                           
                      Nicol, J. Zbasnik                       

  Cryostat to tunnel, Fermilab and CERN / Nothing defined.    Oct 1, 1999
  e.g. vacuum vessel  T. Nicol, R.                            
  feet, alignment     Ostojic                                 
  fiducials, etc.                                             

  Magnet and          Fermilab and KEK /  Unknown. Need axial Jul 1, 1999
  instrumentation     Cold mass design    and radial          
  lead design and     team.               positions and space 
  expansion lead                          requirements.       
  design.                                                     

  Absorber design     Fermilab / T.       Physical envelope   Jul 1, 1999
  (TAS 2 and TAS 3).  Nicol, N. Mokhov    and position        
                                          defined. Need       
                                          detailed design.    

  Cryostat to         Fermilab / T.       Need attachment and Oct 1, 1999
  absorber            Nicol, N. Mokhov    installation        
  connection.                             scheme.             

  Corrector final     CERN / R. Ostojic   MCBX prototype II   Jul 1, 1999
  designs (MCBX,                          design received.    
  MCQS).                                  Need final designs  
                                          for both.           

  Corrector to cold   Fermilab / T. Nicol Nothing other than  Oct 1, 1999
  mass connections                        position defined.   
  (mechanical and                                             
  electrical).                                                

  Beam position       CERN / R. Ostojic   Preliminary         Jul 1, 1999
  monitor final                           physical envelope   
  design.                                 received. No        
                                          details received.   

  Beam position       Fermilab / T. Nicol Nothing other than  Oct 1, 1999
  monitor to cold                         position defined.   
  mass or cryostat                                            
  connections.                                                

  Q2a to Q2b cold     Fermilab / T. Nicol Nothing other than  Oct 1, 1999
  mass connection.                        position defined.   
                                          Relies on MCBX      
                                          design.             

  Q2a to Q2b cryostat Fermilab / T. Nicol Nothing other than  Oct 1, 1999
  connection (vacuum                      position defined.   
  vessel, shields,                                            
  piping, etc.).                                              

  Beam tube           Unknown             Unknown.            Jan 1, 2000
  configuration.                                              
  ------------------- ------------------- ------------------- ------------

##### SUMMARY

It is important to keep in mind that the cryostat design described here
is very preliminary. Much work needs to be done to address the unique
requirements of the design, to address all the outstanding issues and
design constraints, and to finalize component sizes, not just of the
quadrupoles, but of all the piping and interconnect components. The
above conceptual design description serves as the starting point for
detailed design, analysis, and R&D activities.