To: Distribution 6 Nov 95 From: Martin Nordby Subject: Minutes of Near IR Engineering Meeting of 3 Nov 95 C-Hook Analysis A first-cut FEA analysis of the C-Hook support for the Support Tube was presented by Rob Richards. This used the baseline working design developed by Martin Nordby, Jim Krebs, and the EC Calorimeter people during the last BaBar collaboration meeting. Rob's analysis showed that the C-Hook sags 0.4 mm due to gravity loads and the weight of the Support Tube. This is more deflection than Martin's rough analysis predicted. Consequently, the natural frequencies of the C-Hook are lower than originally predicted: First mode: 23 Hz. Yawing motion due to twisting of the C-Hook vertical pieces Second mode: 29 Hz. Axial motion, along the detector axis. The lateral stiffness of the C-Hook is about 1.68 microns / (lb lateral force). This translates to a 4 mm lateral motion for a 1g lateral earthquake load. Since the gap between the Support Tube and the Drift Chamber is only 5 mm, this motion of the C-Hook is clearly too large. The next step in this analysis is to optimize the design to increase its torsional stiffness, while trying to reduce the material at small radius. This will minimize the interferences with the door and Q2 shielding plug. RF Pick-up Dave Coward brought up the issue of shielding detector components from the beam RF. This includes not only the high-frquency bunch-to-bunch RF, but the kHz-level RF from the clearing gap orbit. Roy Kerth reported the the SVT is planning for RF shielding both inside and outside the SVT. They have a copper (aluminum?) clad carbon fiber tube between the IP beampipe and the first layer of silicon (Mike Sullivan was interested in the thickness of this, since it will help reduce the synchrotron radiation background on the silicon). On the outside, the entire SVT and cables will be shielded with a thin RF shield. This is inside the Support Tube, extending out to the ends of the tube. In addition to these, there was a consensus that we need a similar shield on the outside of the Support Tube. This should be fairly straightforward to do. Dave Nelson will expand on this discussion next week. Backward End (HEB Upstream) Interface Issues We "talked over" a set of drawings of the backward end components. These represent the latest design of both machine and detector components. We identified a number of issues which need to / are being resolved. Some are direct interferences, and other are more subtle problems. Below is a list of these issues, and who is working on them: Q2 Shielding Plug How to bring out DC cables through slots in the plug? Dave Coward and Joseph Rasonne are looking at reducing the ID of the removeable part of the plug. Interface with the raft: how is the Support Tube supported through the plug? How does the raft tie to the ID of the strong support tube? (M. Nordby) How are the plug pieces removed? What does the track system look like (M. Nordby) DIRC Horse Collar This has been stiffened at the top and bottom to allow the solenoid chimney to come out at 12 o'clock, but the analysis has not been re-run. (L. Dittert, J. Krebs) Q2 Magnet The new working design for this magnet is a permanent magnet, non-septum design. It takes up much less room, but appears to cost more, and its center is moved out-board from the CDR design. Look at optics implications of moving effective center of Q2. (M. Sullivan) Layout Q2 design and put it on overall layout drawing. (D. Humphries, M. Nordby) We still need answers on the effect of cutting the Q2 shielding at both ends. This requires a 3-D magnetic analysis of the detector. (O. Fackler, H. Lynch, T. Mattison) DIRC Magnetic Shield How to route D.C. cables through/around magnetic shield tube of DIRC. Specifically, what do slots look like on the out-board end of the DIRC shielding? How/where are D.C. racks mounted? Jim Krebs raised the option of mounting the racks on either the Raft support feet or on their own mounts, out-board of the end of the DIRC shielding. This takes up otherwise-clear floor space. This needs to be laid out (J. Krebs, D. Coward) Can the DIRC shielding be supported off the door foot? What are seismic motions with respect to the DIRC tank and Raft? (J. Krebs) Q2/4/5 Raft The existing "diving-board" design for the raft may not fit with the new DIRC magnetic shielding design. New Raft design options must be worked-up to look at mechanical interfaces, and ease of removing the Q2 magnetic shielding and access to the D.C. (M. Nordby, J. Krebs). The Raft support base must also be roughed out. First, its approximate footprint on the floor should be reserved. Second, approximate thermal analysis should be done. There is some concern that mounting the D.C. racks on the Raft supports may introduce excessive thermal motions to the Q2/4/5 magnets. (M. Nordby) IR2 Hall Floor Plan A layout of the entire IR-2 hall and tunnel mouths is needed so space can be reserved for major components. This includes: Raft support feet, door tracks, electronic racks, and installation space. (J. Krebs) At each tunnel mouth, we should plan on a 1/8" - 1/4" thick lead wall, similar to what was used for PEP. This should be "removeable" (with minimal difficulty) to make installation/removal of machine components straightforward. Seismic Isolators The decision to use or not use seismic isolators seems to hinge on a handful of key questions: What are the clearances needed, and relative motions expected for detector and machine components both inside and at the ends of the detector (with and without isolators)? The DIRC horse collar has been stiffened to reduce its seismic yawing motion, but an updated analysis is pending. What are the new deflection numbers. These upgrades are generally considered as good as it can get. Can the Barrel Calorimeter supports withstand the peak seismic loads if isolators are not used. If not, how bulky would they need to be made to take these loads? The present design of the IFR can not take the full lateral EQ load, but Jim Krebs reported that the consensus is that it should be stiffened anyway, regardless if isolators are used. Can the C-Hook on the Forward end (HEB downstream) be stiffened to minimize peak deflections in a non-isolated EQ? This must be done without significantly increasing the size of the cut-out in the detector door. These issues will be worked on by M. Nordby, J. Krebs, and H. Lynch, with reports back at future meetings. Diagnostics for the I.R. Stan Ecklund presented a first-cut list of diagnostics for the I.R. This includes: Temperature monitoring of machine components, RGA on the vacuum system, real-time alignment monitoring, beam-loss monitoring, SR fan position information on the dumps, bunch timing info at the I.P., and a Luminosity Monitor to detect the collision axis and angular spread. These monitors, and the information they collect, need to be tied into the machine- and detector protection systems. This raises the issue of what are the abort criteria for the various monitors, especially with respect to protecting the detector from high backgrounds and during injection. More work and discussions on this topic will be forthcoming in the months ahead. These minutes, and agendas for future meetings, are available on the Web at: http://www.slac.stanford.edu/accel/pepii/near-ir/home.html