From: "Francesco Ruggiero" To: "Bruno Zotter" ; "Daniel Schulte" ; "Elias Metral" ; "Frank Schmidt" ; "Frank Zimmermann" ; "Gianluigi Arduini" ; "Helmut Burkhardt" ; "Hiroshi Tsutsui" ; "John Jowett" ; "Robert Gluckstern" ; "Stephane Fartoukh" ; "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 18 July 2003 Date: Friday, July 18, 2003 5:02 PM ---------------------------------------------------------------- Minutes of the ABP-LCE team meeting of 18.07.03 present: TdA, WH, FR (secretary), LV excused: AK, EM, DS, EV, FZ ---------------------------------------------------------------- TdA recalls that FR should name some "young users" of the impedance database program ZBASE. ACTION -> FR will discuss with EM, DS, and FZ and then inform TdA. LV confirms that the collimator resistive impedance computed by HT is in excellent agreement with his previous estimates. However there is a significant disagreement concerning the effective impedance. This can be traced back to the fact that, according to LV, fast waves on a train of rigid bunches can not stabilize slow waves. The effect of a 2 micron Cu coating on a Carbon collimator jaw is to reduce the transverse impedance at all frequencies above ~10 MHz (see enclosed slides). For very low frequencies, in the 10 kHz range, there is an increase of the impedance caused by the fact that image currents have to flow in the thin Cu layer. Although it is intuitively clear that a Cu coating should help, especially in view of the limited power of the transverse feedback system available at ~20 MHz, Fig. 10 in the draft report by HT seems to indicate that the real effective impedance for the most unstable multi-bunch modes is actually increased by the metallic coating. ACTION -> LV will further clarify the differences of his approach compared to the standard approach by Sacherer, Chao, and HT. Discussions with HT will continue next week to clarify the implications of Fig. 10, before HT's report is published. FR reports about a discussion with Ralph Assmann about future collimator impedance studies. 3D calculations with GDFIDL will be needed soon for several alternative geometries, including possible L-shaped collimators. The LCE team member who will perform these simulations should also attend the meetings of the LHC Collimation working group. Fritz Caspers will perform transverse impedance measurements with two wires, using movable collimator jaws housed in a suitable (LEP?) tank. The possibility to perform impedance measurements with two bunches at the SLAC test facility will be further investigated and a collimator survival test, possibly also with impedance measurements, is forseen in the SPS by September next year. FR reports that AK has succesfully implemented the fast resistive wall kick summation with discretized version of the convolution theorem. The gain in CPU time for the case of the LHC is by orders of magnitude. ACTION -> AK will now include a model of the feedback system and apply his code to study injection oscillations in the LHC. WH reports about a meeting on future beam-beam tracking studies. Next week he will attend the LHC Optics team meeting and discuss the best strategy to share the work concerning tune scans for dynamic aperture. The LCE team will contribute to tracking studies to investigate alternative crossing schemes and compare them to the nominal H-V scheme. TdA needs read-access to ZBASE files under HT's AFS account in order to merge the wake interpolation routine with the version of ZBASE recently modified by OB. TdA also reports that he has suggested some CVS instructions to overcome the problem with the LineFeed at the end of each line in the ECLOUD code. ACTION -> TdA will merge the wake interpolation routine with the new version of ZBASE as soon as he can access HT's files. After the meeting FR has contacted HT and now the problem should be solved. ACTION -> FZ will implement the suggestions by TdA or report back on possible outstanding problems. The next meeting of the LCE team will take place on Friday 1st August. -- 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/