From: "Francesco Ruggiero" To: "Bruno Zotter" ; "Daniel Schulte" ; "Elias Metral" ; "Frank Schmidt" ; "Frank Zimmermann" ; "Gianluigi Arduini" ; "Helmut Burkhardt" ; "Hiroshi Tsutsui" ; "John Jowett" ; "Robert Gluckstern" ; "Werner Herr" ; "Luc Vos" ; "Maxim Korostelev" ; "Alex Koschik" ; "Eric D'Amico" ; "Walter Wittmer" ; "Gregory Penn" ; "Lifshitz Ronen" ; "Elena Benedetto" ; "Elmar Vogel" Cc: "Jean-Pierre Riunaud" ; "Karlheinz Schindl" ; "Louis Rinolfi" ; "Michel Martini" ; "Oliver Bruning" ; "Roberto Cappi" ; "Charles Hill" Subject: Minutes of LHC Collective Effects team meeting 4th July 2003 Date: Friday, July 04, 2003 8:25 PM ---------------------------------------------------------------- Minutes of the ABP-LCE team meeting of 04.07.03 present: TdA, WH, AK, FR (secretary), HT excused: DS, EM, LV, FZ ---------------------------------------------------------------- FR says that the contribution on Collective Effects to the new LHC design report should be considered as a top priority task, especially in connection with related contributions from other groups. At the moment there is only a (rather complete) draft of section 5.08 on Beam-Beam Effects by WH and a skeleton of section 5.04 on Electron Cloud Effects by FZ. The next priority task is to document and publish the recent work done on LHC collimators and MKE kickers. ACTION -> everybody AK asks where he can find the nominal LHC bunch filling scheme, not accessible through the official LHC web page. WH replies that it is accessible through the beam-beam web page at http://wwwslap.cern.ch/collective/zwe/lhcbb/. HT reports about ongoing work on the SPS MKE kicker impedance, power deposition, and collimator impedance. Bunch power spectra recently measured at the SPS by the RF group are not yet available. HT has an analytic model of the kicker impedance and will give an analytic estimate of the power deposition as a function of the bunch length (e.g. for Gaussian bunches). He has HFSS results for the geometric impedance of the LHC collimators including a finite collimator resistivity. The results are in quantitative agreement with the estimates by LV. HT is also investigating the case of electrically isolated collimators, proposed by F. Caspers. ACTION -> HT will publish soon a comprehensive report: a draft will be available before the end of next week (when he will leave CERN). AK has discussed his future working plans with FR. He has implemented a test fortran code for the fast computation scheme of the multi-bunch multi-turn resistive wall kicks using convolution theorem and FFT. A problem related to the linking of a library for the FFT module has been solved and the code now runs under LXPLUS. After a few further checks it will be turned into a working subroutine. ACTION -> AK will use the new code, also including resistive wall with the inductive bypass effect (impedance is sufficient instead of wake?), resonator impedance and space charge, i) to clarify previous discrepancies with analytic estimates of resistive wall instability growth rates, by increasing the multi-turn memory for the wake calculation, ii) to study injection oscillations and emittance growth in the LHC including a model of the feedback system, iii) to analyze future SPS measurements in collaboration with H. Burkhardt and if possible iv) to interface his simulations of multi-bunch instabilities to the LHC impedance database. FR remarks that for a proper modelling of the feedback system AK should discuss with L. Vos, W. Hofle, and also with our new fellow Elmar Vogel. TdA reports that CVS will be used to maintain and upgrade the ECLOUD code under LXPLUS. A minor problem, related to Line-Feed conversion of the binary source, should be solved soon. He also reports that he is currently working on the plotting routine of MADX and that GG is preparing a new INB report (Installation Nucleare de Base) for the LHC: the new LHC design report may be useful in this respect. WH reports that the LHC crossing scheme has been slightly modified by the Optics team to increase the available aperture in the triplets. The new scheme has ~0.5 mm transverse offsets of the collision points and will presumably require rubber-stamping by the experiments (LEMIC+LTC?). Meanwhile WH will estimate orbit effects with beam-beam and the new crossing scheme. Although the differences will be small, we should be prepared to use the new scheme in case it is adopted for the LHC design report. In connection with concerns recently expressed by FZ about the long term stability of the collision point at the SLC, where the IP moved by about 1 mm over a few weeks, WH reports that at LEP the fill-to-fill stability of the collision point was much better than 1 mm. At the LHC we can rely on "golden orbits" and BPM reproducibility of 10-20 microns as well as vertex measurements by the experiments with a few micron accuracy. P.S. At the Accelerator Performance Committe meeting in the afternoon, R. Garoby has reported that the 75 ns beam for LHC is likely to have 1-10% of the intensity distributed in ghost bunches or uncaptured beam. What is the maximum acceptable limit to avoid electron cloud effects? And what about maximum acceptable beam losses at the start of the ramp? -- E-mail: Francesco.Ruggiero@cern.ch, Location: Building 9/1-008 Address: CERN, A&B Division, CH-1211 Geneva 23, Switzerland Telephone: +41 (22) 767 3726 or 767 5272, TeleFax: +41 (22) 783 0552 WWW: http://wwwslap.cern.ch/~rgo/