Minutes of the Mucool meeting, Aug 6 1999. Present: Fermilab : J. Norrem, S. Geer, A. Tollestrup, P. Spentzouris, A. Moretti, W. Wan, R. Raja, M. Popovic, Zubao, ... Phone Connection: B. Palmer, BNL. (possibly others) Scribe: P. Lebrun. I. X-ray flux and energy spectrum measurement from r.f. cavity Speaker: Jim Norrem MuCool proposes to use low pressure TPC to reconstruct muon tracks in a solenoid-based spectrometer. These chambers will be located a few meter (or less) from the cooling apparatus. Almost by definition, the cooling channle contains high power r.f. cavities for re-acceleration. The X-ray emission from the cavity could generate unbearable backgrounds in the TPC. Jim presented measurements made by T. Krock from FNAL, collected by Al. Morretti. These measurements around a section of the 805 MHz LINAC, at FNAL. Behind a 3 feet concrete wall, the dose is about 2 mrem/h. Without shielding, it is 2 rem/h. This translates to 10^6 one MeV photons/cm^2 per sec, or 10^8 10 KeV photons /cm^2/sec,.. E rough estimate of the flux of photon conversions in the volume of the TPC (assuming a pressure of 8 Torr, methane gas) is about 1,000 /cm^2/sec, at 1 MeV. This number by itself is not overwhelming, given the 500 microsecond time window/trigger and the granularity of the device. However, the chamber will also be sensitive to softer X-ray's, so we need to measure... Jim is currently assembling a simple X-ray spectrometer at Argonne, close to a 1.3 GhZ, E < 120 MV/m. single cell, test cavity. The cavity can be in a 0.1 T. solenoidal field, to deflect low energy electron (coming from "dark current" or field emission). The X-ray will come out of the cavity through a Beryllium window, and will be collimated before reaching the detector. Foil of different materials (light Z) can be placed in between, in order to provide a crude measurement of the energy distribution (the absorption depends on the Z of the material and the energy). When these measurement are done, similar measurements could be done at FNAl, Lab G, with the high-power 805 MhZ cavity. 2. Status of Lab G preparation and 200 MhX cavity design (Al. Morretti). a. Lab G. Al reported on the site preparation and installation schedule to conduct the high-power 805 MHz cavity test at Lab. G. Drawing of the 20' by 24' cave (3' feet wall) were presented. Location of the climate control, cryo equipement, water cooling, heat exchanger, modulator racks, pulse forming network cabinets were discussed. Things are coming together: - the first test ofthe modulator will be conducted on Sept. 6 - The 5T. solenoid will be delivered in the first or second week of September. Mike Green (LBNL) recently caled Al, stating that this magnet is "physically complete", the testing at LBNL will start taking place on Aug. 23, and is expected totake 3 days. Mike volunteered to come and visit us, he will tentatively give a MuCool presentation on Friday Aug. 20. FNAL Safety people have been extensively briefed on our program, they currently think that our apparatus will qualify. b. 200 MHz cavity design. Al presented 4 designs, based on MAFIA (3D code) and SuperFish (2D code for cylindrically symmetric pillbox) calculation. Electric field maps were shown. The geometry of these cavities goes as follow: - Semi Open design, featuring two set of rods, crossing at 90 degrees, across the aperture. (e.g., 8 rods) Presumably these rods could be made of light material (e.g. Beryllium), as they are in the path of the muon beam. -Remove the central rods in the previous design, leaving a 16 cm (radius) opening for the beam. - Pillbox cavity, with foils. - Open Iris In all cases, the Iris has a radius of 32 cm. B. Palmer noted that the rods is a good idea with respect to mechanical/thermal engineering. The electrical charactristics are (all of them deliver the required peak field on axis, 15 MV/m). (no transit time factor) Type Z0 (MOhm/m) Q Power(c.w., in MW) Peak Field (MV/m) Pillbox 47.6 74,000 3.0 15 8 rods 32.0 63,000 4.6 24 4 rods 20.0 63,000 7.3 40.2 Open 10.0 63,000 14.6 40.7 The KilPatrcik limit is 14.7 MV/m at 201 MHz. Either we are well above that limit, or we put material in the beam. The scribe ventured that, at these large emittance, cooling is not necessarily dominated by multiple scattering consideration. Bob P. took exception at this statement: what matter is the ratio between the average scattering multiple angle and the average angle at beta min. To maximize cooling and yet have a sound transport system, track angle are typically 300 mRad, independent of the transverse emittance. Thus, multiple scattering always matters, imposing the same restriction on the amount of material. (The scribe is not entirely satisfied with this argument, however: The argument above works at fixed momenta. At large emittance, it is possible to reach ~ 300 mRad angles at a relatively higher momnentum, at a fixed maximum field (say 5 to 10 T.). This should help, because multiple scattering angles are inverserly proportional to the momentum. Thus, one could think about a channel where beta is almost constant, the absorbers are the cavity foils/rods, and the lattice is there to provide cancellation of the canonical angular momentum. The drawback is that we must have relatively high field everywhere, surrounding the large cavitities => phenomenal stored static energy from intense magnetic field over a large volume. To be discussed more..)