To: Distribution 29 Jan 96 From: Martin Nordby Subject: Minutes of Near IR Engineering Meeting of 26 Jan 96 YOUR SUBSCRIPTION IS EXPIRING!! As the distribution list grows and slowly engulfs the entire first page, I would like to trim down the mailing to those people who are actually interested/obligated in this meeting (Thereby saving old growth forests and Postmen's backs!). Therefore, if you have not attended this meeting in quite a while, please e-mail me with you preference (nordby@slac.stanford.edu): 1. Continue receiving announcements, electronic minutes, and hardcopies 2. Receive only electronic announcements and minutes (no hardcopies) 3. Do not receive anything ("Take me off your mailing list") I will give you a few weeks, and if I have not heard from you, will "cancel your subscription." (Agendas and minutes will still be posted on the Near-IR Web pages, so they will still be available.) General Announcements We have two new people in the IR Group: Scott DeBarger and Catherine Carr. They will be focussing their efforts on the Machine/Detector Interface issues, especially the machine support and alignment systems. Welcome aboard. Forward Q2/4/5 Raft Base Footprint Martin Nordby presented a layout of the footprint needed for the Forward Q2/4/5 Raft base structure. The Raft Base in-board support is a single 10" x 10" structural steel column, which extends up through a notch in the foot of the door. All dimensions use a newly defined "IR Reference Frame": Right-handed coordinate system with +Z-axis = parallel to the IR-2 building control line, through the Interaction Point, pointing in the HEB direction, +Y-axis = vertically up. The notch in the door starts at Z = 3719 mm, and ends at Z = 4481 mm, and extends from the split-plane of the doors to X = +/-381 mm The Base structure is essentially an A-Frame to maximize stiffness, with the in- board A-frame leaning inward to avoid the door path as it opens at 18 degress. Bob Bell says that the opening angle of the door is fairly arbitrary, and could be reduced if it helped the design of the Base structure. The current Cantilever Raft and Base design provide room to withdraw the F- Calorimeter 1 m in Z, which provides about 50 cm of opening between the Aero- gel and the Barrel Calorimeter. David Coward expressed concern that this is not much room to squeeze in to work on the Drift Chamber. Furthermore, there is not yet any provision or planning for the platforms which need to fit in this region for personnel access. If this 50 cm gap needs to be increased, it may affect the design of the cantilevered part of the Q2/4/5 Raft, so this is an important issue to agree on. Towards that end, David suggested making a plywood model of the Forward End, similar to the one being done for the Backward End. This would include a F-Cal and ATC, Drift Chamber end plate, Barrel Calorimeter, Q2, Q4, the Raft, and Support Tube. Alex Grillo epressed interest in using this to better understand the access for SVT ribbon cable connections just beyond the end of the Support Tube. Getting back to the Raft base: The A-Frame Base does not now incorporate any support for platforms for personnel access to the beamlines, nor for mounting the F-Calorimeter removal fixture. These could either mount off the existing Base, or be incorporated into an independent support. Q2 Vacuum Chamber Lou Bertolini and Bob Holmes have developed new cross-section layouts for the Q2 LEB Chamber running through the Q2 P.M. magnet. These cross- sections incorporate essentially the "latest thinking" for the design, pushing coooling channels as close as possible to the SR strike fan, increasing the BSC size to match the BSC for the new Q2 position, and offsetting the Q2 magnet vertically. Since the P.M. material strength varies with temperature, Q2 must be kept at a constant temperature to better than 2 ¡C. This places tough requirements on the chamber, which is being hit by kW-levels of SR. Although the new layout squeezes as much as possible out of the space, it was not clear if the thermal analysis would bear out the design. Lou will be working on the analysis this week. Another concern was raised about how a thinner copper chamber (3 mm behind the SR strike region) would shield the P.M. material in Q2 (and the detector). Elsewhere in the machine, copper chambers are 5 mm thick for shielding purposes only, but here, there is only room for 3 mm. Solenoid Stray Fields in Q2 Tom Mattison investigated the effects of stray solenoid field from BaBar on the Q2 HEB magnetic shielding. This is a 1 mm shield around Q2, but was modelled as a 2 cm thick iron cylinder, with a 6 cmm inside radius, 40 cm long. The assumption is that the field in the shield will scale linearly with thickness. For this geometry, and a 100 G ambient field (the max field leakage spec'd for the Q2 shielding plug), the field in the thick shield is 6000 G, which scales to 60 kG for a 1 mm thck shield (assuming no saturation). To prevent saturation in real iron, the ambient field would have to stay below 15 G, which has never been attained, even with the best Q2 shielding plug design. There are a few options which minimize this problem. First, since the HEB shield is trying to shield fields mostly in the X/Y-plane, segmenting the shield in Z should not affect its shielding ability, but make it literally less attractive of Z- oriented stray fields from the solenoid. Using seven 1 cm wide gaps along the length of the original shield, Tom cut the field in the HEB shielding by 75%. Other possible options are: --Extend a thick shield all the way around both beampipes to protect Q2 from the stray solenoid field, then use a thin "septum shield" between beampipes as a HEB shield which is protected from the solenoid field. --Avoid cylindrical shielding altogether by possibly increasing segmentation again (David Humphries already saw a large reduction in stray field when segmentation increased from 16 to 24 blocks). Also, to attack the end effect stray fields, look at using "mirror-plate" type disks on the ends. More investigation is needed on this, both from the solenoid and Q2 directions. These minutes, and agenda for future meetings, are available on the Web at: http://www.slac.stanford.edu/accel/pepii/near-ir/home.html