----------------------------------------------------------- Minutes of the ABP-RLC team meeting of 19.05.2006 present: EM, WH, TP, GR, RT, FZ excused: UD, FR web site: http://ab-abp-rlc.web.cern.ch/ab-abp-rlc/ ------------------------------------------------------------ (1) Minutes of Last Meeting, Pending Actions -------------------------------------------- Actions from 05.05.2006: => ACTION => Discussion with Elena Shaposhnikova & rf group on strategy for longitudinal parameters at LHC injection (FR). Pending since FR is absent => ACTION => SPS e-cloud simulations at 26 and 60 GeV for a dipole field (GR). Simulations were run for the two energies and also for 450 GeV, both without field and for a dipole. The 450 GeV case is more stable thanks to increased longitudinal emittance. => ACTION => Contact rf group for possibly higher-quality bunch profiles (GR). This question was addressed in the APC of 18.05.2006. Higher resolution is possible with the Faraday-cage scope according to Thomas Bohl. Other and older actions: => follow-up impedance of LHC septa, 07.04.2006, EM PLANNED => add 2003 minutes and presentations to the RLC web site, 17.03.2006, FZ IN SLOW PROGRESS => contact D. Macina to organize meeting with experiments on TCTV aperture, 17.03.2006, FR STATUS UNKNOWN => contact M. Mayer to question chamber dimensions, 17.03.2006, EM, AG PROBABLY DONE, TO BE CHECKED WITH AG => contact Stefano Redaelli to clarify number of TCTV, 17.03.2006, EM, AG DONE, RESULT PRESENTED ON 07.04.2006 by EM => GR and FR will follow-up ideas on debunching transverse impedance measurements with GA, EM, and FZ, 10.03.2006 PLANNED. FZ commented that raw data from earlier MD should be available from Thoms Bohl. He recommended performing a HEADTAIL debunching simulation, with for example 2 resonators, to check whether growth rate indeed is proportional to impedance at the chromatic frequency. EM reported that the FP420 Cu-pipe thickness was checked. It is only 200 micron instead of several cm. Federico Roncarolo is now re-computing the impedance as a function of the Cu thickness. WH encouraged all RLC members and friends to inspect the list of actions posted at http://ab-abp-rlc.web.cern.ch/ab%2Dabp%2Drlc/Actions/actions.htm and to send any comments to FZ. Especially team members should let it be known when an action under their responsibility has already been completed and reported. (2) Follow-up of GSI-CERN Meeting: Simulation Results from Burkhardt Doliwa on SPS MKE Kicker Impedance and Numerical Results from Rainer Hasse on LHC Collimator (EM) -------------------------------------------------------------------------------------- At GSI, it was agreed that the Darmstadt team computes the impedance of SPS kickers and LHC collimators using their own simulation programmes and formulae, respectively, for benchmarking purposes. The impedance of the SPS MKE kicker was simulated by Burkhardt Doliwa, using his code, which was developed in the group of T. Weiland. Both real and imaginary part of the simulated kicker impedance are close to the curves which EM has computed previously using either the Burov-Lebedev or Bruno Zotter's theory, as well as to the result of the two-wire measurement by Fritz Caspers and Tom Kroyer. EM and GR discussed that in order to include the kicker impedance in the HEADTAIL code, either the wake field of AK could be used, which corresponds to Luc Vos' approximate bypass impedance, or a new wake field may be derived possibly starting from Bruno Zotter's most general expression. Rainer Hasse has numerically calculated the impedance of an LHC collimator in the LHC and in the PS booster, respectively, using Al-khateeb's formulae. The PS booster case was chosen for investigating the effect of a beta much smaller than 1. The impedance was computed with or without the space-charge contribution. All the results are preliminary. The transverse impedance from Rainer Hasse peaks at about the same frequency, ~1 MHz, as the one computed from B-L's or Zotter's theory, but the value of the maximum impedance is larger by a significant factor. Also strikingly, in Rainer Hasse's calculation the imaginary part of the impedance approaches zero for low frequencies and not a constant large value. The large differences between the CERN and GSI results need to be clarified. Rainer Hasse has also computed the longitudinal impedance, for which no CERN prediction exists. Unlike for the transverse case, the imaginary component of the longitudinal impedance goes towards a constant large value as the frequency decreases. FZ suggested to calculate the longitudinal impedance using the old LAWAL code. Even if not fully exact, it might allow for a verification of the order of magnitude at least. EM informed the team that the derivation of the longitudinal impedance will be a first task of the new student, Benoit Salvant?, together with debugging the transverse notebook of Bruno Zotter (the impedance values derived by which appear to be closer in magnitude to Rainer Hasse's, as remarked by FZ). (3) AOB ------- If FR does not return next week, the meeting on 26.05.2006 (Friday after Ascension) will be cancelled. Posted on the web: Slides by EM Web site: http://ab-abp-rlc.web.cern.ch/ab-abp-rlc/