minutes ABP-LCE meeting 31.01.03 present: Td'A, JG, WH, JJ, AK, EM, BM, GP, RP, DS, FR, LV, FZ ------------------------------------------------------- (1) There were no remarks on the previous meeting or minutes. (2) In response to the estimated loss of longitudinal landau damping by FZ in the previous meeting, and the ensuing discussion on different treatments, Elias Metral presented a beautiful analysis of the longitudinal stability criterion for dipole and higher-order modes, including synchronous phase shift and potential well distortion. He showed that the latter give rise to a correction factor which increases the threshold found by Boussard&Brandt&Vos by a factor 1.4 for the LHC inductive impedance. Jacques Gareyte presented historical calculations by Besnier for space charge below transition, which also apply to an inductive impedance above transition. These show that the coherent tune shifts into the incoherent frequency spread exactly when the spread is equal 4 times the tune shift. This is the same criterion as found by Elias and used by BBV. Slides of EM's and Jacques' presentations are attached. (3) Francesco Ruggiero (and Luc Vos) presented draft slides on collimator wake impedance in preparation for a meeting of the collimator working group. Only general guidelines were given, in particular, any thick insulator should have a thin metallic coating of several skin depths, and low-frequency resonances can arise in thick dielectric layers. Thin layers might be ok, as resonant frequencies move out of the bunch spectrum. Microbunching could still occur. Hidden metallic layers under a thin dielectric could ensure reasonable impedance below 50 mOhm, while avoiding metal on the surface. The heating for graphite jaws would be about 1 kW at top energy; while it would be 10 kW for ferrite material. It was also pointed out that at high frequencies the image current follow the collimator geometry and are independent of the conductivity (thesis by A. Mostacci). An AB note on the effect of thin metallic coating summarizing the CERN results has just been published. Slides are attached. (4) FZ reported of the ongoing discussion on the location of the rf buttons to be installed in the SPS. Presently favored locations are in BA2 and BA3. A meeting will be convoked next week to finalize the choice of position. A meeting was held with Ian Collins, Roberto Cimino and John Byrd where recent measurements of secondary emission and electron reflections at low incident energy, experiments on photon backscattering, the initial photoelectron energy spectrum, and possible future studies including contributions from the LBL/ALS were discussed. Our present simulation model is not consistent with the secondary emission yield at low energies. DS mentioned that in the APS 1-3 eV electrons are dominant. (5) Follow-up on actions and round-table discussion of ongoing activities. ACTION FR -> ask for disk space (e.g. for electron cloud) LV in discussion with Rathjen and Veness from the vacuum group on recombination chambers in IP2 & IP8 and the welds in the warm parts of the machine. DS attended Daresbury DR2003 workshop. E-cloud effects are relevant for linear colliders. S. Heifets points out that plasma effects must be taken into account. Input data from surface measurements are very important, incl. temperature dependence and surface roughness effects; bias voltage of 10 V is required for reliable results. JJ - agenda of LHC MAC in March is prepared. Only LCE contribution is by FZ on electron cloud. Steering for LHC ion project has been set up. ACTION JJ -> Report on tracking with imperfections and beam-beam in the coming weeks GP - CLIC studies BM - discovered that MAD-X gave different results on different lxplus machines; problem is understood (WH) ACTION FS and WH -> will inform LHC optics team BM also studies luminous regions for ions. AK - working on code originally developped by A. Wagner and J.-L. Sabbi that computes multi-turn multi-bunch wake field effects; AK checked that code uses correct units, but the kicks are still too large for reasons yet to be understod; applications to the SPS and LHC; presently res.wall ACTION AK -> 2 bunch calculation, with improved SPS impedance model, also including space charge, res.wall, by end of February RP - prepares seminar for Hamburg, finishes thesis on Landau damping due to overlap of pi mode with synchrotron sidebands WH - exercising MAD-X to study effect of linear imperfections on beam-beam; footprints, geometry, PACMAN bunches; also developing strong-strong model including PACMAN; completed two reports on different crossing schemes and aperture & beam-line stability for TT41 LHC commissioning options are under study for Chamonix; 75 ns spacing and low-luminosity operation at 1e33 (2 options with same brightness and different beta-star) ACTION FR WH -> FR will send relevant informations to beam-beam team ACTION FZ DS -> stricter handling of ECLOUD code; fix date to freeze the code, incl. input file and example; introduce version numbers, and documented changes; tracing of old versions; use cvs; time scale 2 weeks FZ - prepares e-cloud talk for Darmstadt, started e-cloud simulations for PS (historical observations), SPS, LHC