Minutes of the IR Engineering and Physics Meeting of 17 May 96 Back End Q2/4/5 Raft Martin Nordby reported on progress on the Back end Q2/4/5 Raft design. Much of the progress has been to identify and locate additional machine components inside the strong support tube and SOB. The actual Q4 magnet has been positioned, and 3/4Ó struts added for supports. These, and the LEB chamber, define the aperture around Q4, and not the magnet steel itself. Just outboard of the end of the SOB, the water lines for the Q4 magnet, and the LEB corrector define the space envelope. Currently, it looks like the Q2 Shielding Plug interferes with the LEB corrector during Plug removal. Orrin Fackler will investigate whether the plug can be shortened, or the out-board end tapered more sharply. Also, we may need to split the corrector to remove the Plug. This will add time to an access, but may be the only alternative. The in-board end of the Raft uses the U-shaped cantilever borrowed from the Forward end. This shape fits tightly around the Q2 magnet and septum chamber, and reaches through the bore of the Q2 shielding plug, avoiding the need for a big cut in the plug for a box-beam. The Raft Base design is also borrowed from the Forward end. The A- frame shape just clears the volume swept by the opening of the DIRC SOB doors. However, the actual door design needs to be incorporated to ensure that this works (Joseph Rasonn will forward the latest 3-D layout of the SOB to Scott Debarger). Currently, the clearance is 135 mm. To maximize the stiffness and stability of the Raft and Base, the Raft must flare out around the Q5 magnet, instead of dropping underneath it. This flare should also clear the SOB door swept volume. However, the tracks for Q2 Plug removal must stay clear of this flare. David Coward reported that the D.C. Cable Requirements paper is almost ready. The current cable cross-sectional area needed is 80 in^2. This includes packing fractions for all cables, and assumes that the transition to fiber optics occurs outside the detector. No progress has been made in finding space for the cables, Q2/4/5 Raft, and Q2 Plug removal tracks in the SOB. Jim Krebs, Martin Nordby, Scott Debarger, and David Coward will continue to work on this. Forward End Q2/4/5 Raft Scott Debarger showed the latest Raft design for the Forward end. This includes U-shaped half-cones surrounding the Q2 magnet and septum chamber. This transitions to a 16Ó wide by 8Ó high box beam under Q4, then flares to two 10Ó by 8Ó box beams straddling Q5. The flare from one to two beams occurs between Q4 and Q5. Total deflection of the Raft is 0.1Ó at either end. This is somewhat higher than hoped-for, but can be easily reduced by moving the outboard support away from the in-board one. The U-shaped half-cones are tapered to fit tightly around the contour of the Q2 magnet and chamber. The total radial space needed outside of the cone which circumscribes the chamber and magnet are: 5 mm clearance between component and support (for alignment and fabrication tolerances); 10 mm for the thickness of the support; 5 mm clearance outside the support for alignment tolerance of the support. In Z, additional space was used around the front of the Q2 magnet, and no chamfer was made on the third finger of the Q2 plug. These realistic clearances tend to incrementally eat away at the Q2 Plug fingers. However, the numbers represent a thought-out design, and are stay-clear values, not nominal dimensions. To buy back some space, James Osborn will look into cutting off the corners of the Q2 magnet mirror plate, or possibly eliminating it. This will open up space at the tightest location: around the in-board corner of Q2. Also, Scott and Catherine Carr will continue to refine the Raft design. However, not included in the design are realistic tolerances for the BaBar Door. The dimensions presented by Scott, and shown in past discussions do NOT include any allowance for the following: Door fabrication tolerances; Plug fabrication tolerances; Plug placement tolerance; Door placement tolerance with respect to the barrel; Door repeatability with respect to the barrel; Barrel placement tolerance with respect to the PEP-II IR. These tolerances were guessed to total 5 mm, which should be added to the clearances. Jim Krebs will try to nail these down more carefully. Another issue which arose is the level of stray field that Q2 can handle. Tests by John Seeman and Zach Wolf, and analyses by Fran Younger show that octupole bucking coils around each pole of Q2 should be able to buck out up to 500 G of solenoid field, with no apparent higher harmonics generated. While this suggests that more stray field could be tolerated, all PEP-II people felt strongly that this should NOT be planned on. We should still design the Q2 Plug to limit stray fields to 100 G (using a 2-D, axisymmetric model). If the real Plug allows more leakage, then Q2 can handle it, but we should not use up all of our margin now. Finally, the U-shaped half-cone cantilever around Q2 has enough room inside it (on paper, at least) to fit all machine services coming out of the Support Tube, and the SVT ribbon cables. Total area available is 600 cm^2 around the in-board face of the Septum Chamber (the tightest spot). However, much needs to fit in this region, including: septum mask vacuum joints; mask cooling water fittings and hoses; wire- and relative- alignment systems; insulation for water lines passing Q2; support/alignment system for Q2 chamber; alignment targets. Martin Nordby will develop a list of all services in this region to identify if room is available for all SVT cables. These minutes, and agenda for future meetings, are available on the Web at: http://www.slac.stanford.edu/accel/pepii/near-ir/home.html