To: Distribution 15 Sep 95 From: Martin Nordby Subject: Minutes of Near IR Engineering Meeting of 15 Sep 95 Announcements The PEP-II IR Group has been reorganized, such that the old "mid-IR" will be managed by the respective HER and LER organizations. For the HER, this includes all components up to, and including, Q4 and Q5. For the LER, this is everything up to the vacuum flange between Q4 and Q5. However, all supports, installation planning, and coordination of designs for PEP-II components for HER/LER commissioning in the IR-2 hall will be managed by the new IR group. This includes interfacing with BaBar subsystems. Furthermore, the new IR group is responsible to design and fabricate components out to the Q2 magnet and chamber. PEP-II BPM Spec's Steve Smith reported on the specifications for the BPM's used in the HER/LER straights, and how the system design could translate to the Near IR BPM at 0.72 m. The BPM system consists of four feedthroughs, with shielded cables running to a Filter/Isolator Box (FIB) within 36" - 80" from the feedthroughs. Cable runs any longer than that would prevent resolving of a single bunch. Because the IR BPM is near the first parasitic crossing of the beams, it will only be useful with one beam stored, or if gaps are added to the bunch train so bunches from only one beam at a time pass the BPM for part of the orbit. Although the relative arrival times of each bunch at the BPM could be used to diagnose a detector background problem, it was agreed that there are better methods of doing this. The FIB box has permanent magnets inside, and radiates 10's of watts, so it will need to be outside the detector field, somewhere. This will probably need space on the outside of the detector. The cables to the FIB are 0.20" diameter, and 100% shielded, with a -200 dB signal outside the outer coax (at Ghz frequencies). Steve felt like the SMA connectors and especially other beamline sources would pose a far bigger cross-talk problem. The long-haul cables from the FIB to the processor box are up to 60 m (o.40" diameter) in the arcs, so we do not have a problem in the IR. Resolution: 1 mm at 5 E8 e-/turn 100 microns at 1 E10 e-/turn 15 microns at 1 E10 e- Resolution scales with 1/(diameter), so the Near IR BPM will be 10% off. Reproducibility: 15 microns elec + 15 microns mech Accuracy: +/- 1 mm with respect to quad centerline Dynamic Range: 1 cm radius circle Precision of current measurement: 10% To maximize the range of the Near IR BPM, its center should be located between the orbits of the HEB and LEB, and not on the mechanical centerline of the detector. It was not clear whether this was possible to design into the chamber. M. Nordby will investigate this. The BPM should be mapped for dynamic range and signal. The Arc BPM calibration fixture may be able to be used, but it may not fit. If needed, the feedthroughs could be tilted to match the contour of the B1 chamber. This will not affect the signal, but may expose it to SR. Mike Sullivan and Martin Nordby will check on this. Near IR BPM Requirements: A First Pass Stan Ecklund presented a first cut at requirements for the Near IR BPM's: To monitor and correct for closed orbit changes, to locate the IP position, position SR fans, and restore/check running configurations, an absolute position accuracy of 500 microns is needed, and a relative accuracy of 50 microns. A relative accuracy of 100 microns will be needed to check solenoid steering compensation. Finally, if these BPM's are used to measure beta, it needs to have a relative accuracy of 0.1 sigma, or 20 microns. All of these values are within the capability of the current BPM's Holes Roy Kerth relayed that, as far as he and others of the SVT collaboration know, they do not need any access holes through the carbon composite Support Tube. However, they also agreed that it never hurts to have a few, just in case... However, since structural integrity, especially resistance to buckling, is critical for this tube, we made a working decision to NOT have any holes in the tube. Holes produce stress-concentrations and can provide weak spots to initiate buckling, so they are generally an undesirable feature.