Minutes of the ABP-LCE team meeting on 09.01.04 present: EB, PE, AK, EM, JRL, FR, DS, EV, FZ excused: WH ---------------------------------------------------------------------- (1) New Members --------------- FR welcomed two new group members, Peder Eliasson (PE) and Javier Resta Lopez (JRL). Both are PhD students supervised by DS. JRL will develop a nonlinear collimation system for CLIC and a possible application to LHC, with help by FZ. PE will investigate CLIC main-beam tuning. (2) Minutes & Pending Actions ----------------------------- OLD ACTION -> FR will contact LV concerning factor 4 Pi. Done. LV has been contacted by email, but no response so far (he is still thought to be in Australia). OLD ACTION -> ZBASE progress & examples Pending. Tutorial by O. Bruning had been suggested. ACTION -> Fr will contact OB regarding tutorial. OLD ACTION -> FR will check the Zbase afs access rights -> DONE All "young ZBASE users" have now read/write access to /afs/cern.ch/eng/lhc/impedance OLD ACTION -> CB head-tail growth rates for updated LHC impedance (FR) Pending. Requires response to JPK. OLD ACTION -> AK will check CB rise time for Roman-Pot impedance. Computation has started, but data have not yet been analyzed. The acceptable Q value is to be determined. OLD ACTION -> Stability Analysis for TOTEM Beam (EM) Done. Draft note by EM & AV was sent to FR & AV. The note displays minimum (for stability) and maximum emittance (for physics) as a function of gap size. OLD ACTION -> Study McGinnis paper and impedance of Schottky monitor for LHC (EV) Done. Number was given in EV's email for 3-GHz and 6 GHz systems (the email is attached). ACTION -> AK will check if the effect is important in simulations. OLD ACTION -> Organize ABP-RF-BDI meeting on beam-beam diagnostics with feedback (EV). EV discussed this with WH. The meeting should focus on beam-beam simulations with feedback and the interpretation of tune-meter measurements for colliding beams. OLD ACTION -> The optics team will be informed by FZ about inconsistencies in BPM numbers and types -> DONE Various formulae for the impedance of a shallow cavity exist (L. Vos, Palumbo/Zobov). The Palumbo/Zobov expression for a tapered chamber gives the opposite sign to that for a shallow cavity with steep edges. OLD ACTION -> FZ will contact M.Zobov. Not yet done. FZ will send email. DS mentioned that he could simulate the cavity with Gdfidl (ACTION?). FR pointed out that M. Dyachkov had a web site with an online program for computing this type of impedances. OLD ACTION -> FZ find web site. Not yet done. FR will help searching for this site at CERN and TRIUMF. -> The CERN web site is at http://wwwslap.cern.ch/collective/misha/. However the cgi-bin script does no longer work. (2) Electron Cloud ------------------ DS presented a draft version of his talk for the LTC (the next meeting has been postponed until after Chamonix). After changes to the code (force at the center no longer diverging and image charges added for rectangular chamber), qualitative good agreement between measurements and simulations. In particular, the effect of a magnetic field is well reproduced, namely the larger electron flux with magnetic field, and the dip in the flux around zero as the magnetic field is scanned from negative to positive values. Which change in the code gave rise to the dip is not known, but this might provide some insight into its origin (EM). DS compared results for 25 ns and 75 ns for the warm and cold strip detectors, and spatial distributions for 3e10 and 5e10 protons per bunch. The simulations rolls off more slowly for higher fields than the observation, which could be due to the effect of the detector holes on the multipacting process (FZ). The stripe position is systematically offset by about 2 mm compared with the observation. FR recommended to add the 2003 data to the plot. DS also simulated the dependence on the chamber height, and found that the largest multipacting occurs for a half height of about 40 mm. Experimental data may not be available from the vacuum group for the variable-aperture detector due to technical problems. DS also compared two different geometries for LHC (original and elliptical) and found almost the same result. This is different from FZ's simulations. The reason why the simulations are different is under investigation. The two versions of the code are not exactly the same. DS showed results for variable number of batches at injection into the LHC. The heat load for the second batch can be 20 times higher than for the first (e.g. 2.5 W/m in dipoles for d_max=1.5). The injection simulations should thus be extended to cover several batches. DS and FZ held a meeting with Vincent Baglin. The minutes are on the web at the meeting site: http://project-ecloud-meetings.web.cern.ch/project-ecloud-meetings/default.htm VB interprets the data as there being no scrubbing at all. FR wondered whether the WAMPAC detectors perhaps measure impedance effects and not electron cloud. VB observed a factor 2 change in the heat load by applying a magnetic field at WAMPAC2 in 2002. EB is continuing the analytical study of the pinch effect and she revised results for the Sacherer distribution. She also conducted HEADTAIL simulations for different tunes. She will report next time. (3) Abstracts for EPAC04 ------------------------ The preliminary list of abstracts was discussed. Several comments were given. EV's paper only focuses on CNGS and not LHC. AK's paper on inductive bypass should include LV as co-author. SPS impedance localization technique, if not converging to unique results at the SPS, could be tried at another machine, perhaps HERA? There should be a paper on HEADTAIL simulations by EB (et al?). A joint paper with Tom Katsouleas on HEADTAIL-QUICKPIC is preferably submitted to ECLOUD'04. FR suggested submitting an overview and comparison of electron-cloud build up and instability codes. Also there is a programmatic paper on LHC upgrades. The last two papers reflect the future ESGARD activities. FR will collect EPAC abstracts from the team and forward them to JPR and later SM. CLIC abstracts should be send to Ian Wilson. (4) AOB ------- The APAC04 abstract deadline is January 17. EM will represent ABP group at this conference. Attached: email from EV on Schottky-monitor impedance.