1. 1 Issues concerning the Design of the Tracker Solenoids Michael A. Green Lawrence Berkeley National Laboratory 17 August 2005

2. 2 Proposed Tracker Solenoid Design Changes Increase the OD of the cryostat vacuum vessel from 1080 mm to 1414 mm. This means that the tracker module is connected directly to the AFC module. There are other implications as well. Redesign the cold mass support to make the magnet assembly and centering easier. Move the coolers and cryostat necks from the end of the cryostat to the center of the cryostat. Redesign the tracker magnet support to the ground.

3. 3 The Genoa Tracker Solenoid Iron Shield End Coil 2 End Coil 1 Center Coil Match Coil 1 4.2 K Cooler Cold Mass Support Match Coil 2 He Cooling Pipe Radiation Shield Al Coil Spacer Ground Support Leg

4. 4 Changing the OD of the Cryostat Increasing the OD to the size of the AFC and RFCC modules means that the tracker module can be connected directly to the AFC module. There is increased space between the vacuum vessel and the cold mass, which will make the tracker magnet assembly easier. The vacuum vessel is divided into three parts a center section and two end hats. The center section has all services and the warm ends of the cold mass supports. More study is needed to see if increasing the OD affects the tracker performance.

5. 5 Cold Mass Support Changes The cold ends of the supports will be between the two match coils at the AFC end. The cold ends of the supports will be between the center coil and end coil 2 at the tracker end. The cold mass support angles will change. There will be less of the cold mass support that sticks out of the vacuum vessel, if the vacuum vessel diameter is changed. With a change in the OD of the vacuum vessel, the tracker magnet assembly should be easier.

6. 6 Changes in the Placement of the Coolers and the Cryostat Necks The coolers will be mounted on the center section of the vacuum vessel, which also supports the cold mass. The magnet leads and cryostat vents will also be located on the center portion of the cryostat vacuum vessel. The center section will also be connected to the ground support structure. One can be flexible about the cooler and lead location along the center section of the magnet vacuum vessel. The exact location depends on other design factors.

7. 7 The Tracker Magnet Ground Support The proposed ground support for the tracker solenoid module is similar to the RFCC module ground support. This support allows all of the magnetic and vacuum forces to be transmitted to the ground. The ground support may connect only the center section of the vacuum vessel to the ground. More study is needed. The RFCC Module RFCC Module Ground Support

8. 8 Concluding Comments A change in the outside diameter of the tracker solenoid cryostat is seriously being considered. Whether this change is made depends on the other aspects of the tracker. The cold mass support will be changed to fit the new cold mass package regardless of the outer diameter. The coolers, the leads, and cryogenic services will be moved to the center part of the cryostat. The support of the tracker solenoid to ground must be changed so the forces can be properly transmitted.