---------------------------------------------------------------- minutes ABP-LCE meeting 28.02.03 present: EB, TdA, JJ, AK, MK, EM, BM, DS, FR, LV, FZ ---------------------------------------------------------------- (1) Discussion of action items were largely postponed to after Chamonix. (2) LHC beam commissioning parameters (FR) New parameter sets are proposed for 25-ns and 75-ns bunch spacing. Main difference to previous cases is that the normalized emittance is kept at the nominal value 3.75 micron, assuming that smaller emittances may not be reached during commissioning. Beam dynamics considerations favor 75-ns spacing (reduced long-range effect, no electron cloud), whereas the experiments are thought to favor nominal spacing and smaller number of events per crossing. FR's slide with parameters is attached. (3) Progress on e-cloud simulations (DS, EB, FZ) Stripe position was simulated with ionization as source of primaries and for different magnetic fields. The observed stripe position is consistent with simulations for a field of 120-150 G, slightly above the nominal field. Also the maximum yield has some influence on the position. Program was debugged and new jobs were submitted for all cases. ACTION FR: Get updated value for the available cooling capacity from L. Tavian Some discrepancies remain in the energy spectrum. ACTION FZ + DS: run simulations without elastic reflection HEADTAIL simulations by EB show a strong emittance growth (this could be due to a small number of macro-electrons; simulations will be rerun with better statistics). DS and FZ have met with A. Ferrari to discuss electron cloud at collimators. AF will run a simulation for 7-TeV protons with impact parameter 100 nm and provide energy spectrum and fluence of secondaries. In parallel we are looking for measured secondary emission yields at keV energies for electrons. (4) Collimator Impedance (LV, et al) SLAC measurements by M. Seidel are slightly larger but consistent with our estimate (less than factor 2 difference). Incoherent resistive quadrupole wake will be implemented in HEADTAIL by EB. EM will collect and survey all available analytical, numerical, and experimental papers on collimator impedance, and maintain overview. The origin for a factor 2 discrepancy in the resistive heating estimated by LV and A.Chao remains to be understood. EM will help in this comparison and report in two weeks. ACTION EM LV will document his calculations for the impedance of coated layers. ACTION LV At top energy, inductive impedance is especially important. Therefore, the idea of using different collimators at injection and in collision may not offer a great relief. FR forgot to mention that there are several collimator-like objects, such as TAS, TCL, TCP, or TCDQ that should still be included in our impedance budget. Steve mentioned that he would like to see the final LHC impedance and instability budget including all sources known today. (5) Beam-beam simulations (BM) Sixtrack simulations are underway for the 75-ns case of FR's commissioning scenario. Simulations will give the dynamic aperture in the presence of head-on and LR beam-beam, triplet errors, and corrections. There will be no LCE meeting on Friday next week, due to Chamonix, and no meeting in the following week, due to the LHC MAC. The meeting could be held at another day of the week, or otherwise on March 21. FR will send out invitations.