----------------------------------------------------------- Minutes of the ABP-RLC team meeting of 16.12.2005 present: EB, UD, WH, DK, TP, FR, GR, FZ web site: http://ab-abp-rlc.web.cern.ch/ab-abp-rlc/ ------------------------------------------------------------ (1) Minutes of Last Meeting, List of Actions (FR) ------------------------------------------------------------ => OLD ACTION => Check exact time distance of bunches (RA) => ACTION => FZ will send a reminder to RA => ACTION => literature search for 2-beam wake field effects (EM, FZ). Bruno Zotter has given to EM two papers on this topic, who has distributed copies to several team members. => ACTION => HFSS simulation (EM, AG), may require 3D drawings, not yet existing Pending. => ACTION => Draw tentative conclusion for two limiting cases (EM) Pending. EM has reported to the APC and will present the results to the RLC team next year. => ACTION => Check adequacy of conducting boundaries (GR) Partly done. The NEXT RLC MEETING will be held on January 14, 2006. On the agenda are a review of pending actions and a presentation of EPAC abstracts. (2) Results of the beam-beam tracking campaign (DK+WH) ------------------------------------------------------ DK presented the results of a dynamic-aperture tune scan in collision. He used a weak-strong model, with collisions only in IP1 and IP5. Two crossing schemes were compared, HV and HH, and both nominal and extreme PACMAN bunches were considered. The tune scan was performed parallel to the diagonal, between Qx=0.25 and 0.33. The vertical tune was chosen 0.01 units higher than the horizontal. A second tune scan with a tune difference of 0.02 units is presently underway. Dynamic aperture was computed by tracking over 1e6 turns, using the BOINC system. Particles were launched along different angles in the x-y plane in steps of 5 degrees. The zero-amplitude tune was set to be the same for all simulations, while in reality the PACMAN bunch would have a different tune in the HHH crossing scheme. Triplet errors and their correction is included. Both the HV and, even more, the HH scan exhibit a smaller dynamic aperture and stronger resonances at angles near the horizontal plane. The dynamic aperture, both loss and chaotic border, are on average about 1 sigma lower for the HH scheme than for the HV one. At angles closer to the vertical, above 45 degrees, the HH scheme shows an enhanced stability, which is basically unlimited near the vertical direction. Chaotic particles are found at 4 sigma for many of the tunes with both crossing schemes and both types of bunches. The question was raised why also the HV scheme is more unstable in the horizontal direction. This is probably an artifact of the working point, above the diagonal. FZ thought that either VV crossing or a working point below the diagonal might look better than the HH case studied. WH described the planned next groups of studies: A. scan at a different distance from the diagonal (in progress) B. scan for VV crossing C. scan with imperfect triplet correction FR suggested to lower the start amplitude of the scans in order to detect the onset of chaos also below 4 sigma. It was mentioned that the simulation did not use self-consistent orbits, which are not thought to be important for this type of study. In the future, DK will spend 30% of his time on LHC which is 'at the corner of his screen'. He will also make a presentation to the LOC on Tuesday 20.12.2005. Presently the BOINC system is not fully loaded. On 19.12.2005, WH will make a clear statement whether we want to continue and how much computing power is needed. If we do not use BOINC with a high average load, it will likely be discontinued. (3) Reports from meetings (LHC-MAC, LTC, etc.) and AOB ------------------------------------------------------ FR mentioned that PAF is presently holding meetings twice per week. A meeting with the DG is scheduled for Monday 19. 12. 2005. PAF's physics counterpart POFPA has been making good progress. It concluded that the first priority for CERN is the LHC luminosity upgrade, followed by the LHC energy upgrade (after successful LHC commissioning). Next in the list of priorities comes neutrino physics, where a decision between superbeam and betabeams has not yet been taken, but is urgently awaited. Lower priorities are assigned for kaon physics, muon physics, ep collider, and heavy-ion physics. FZ reported on the LHC MAC. Recent LHC progress was applauded by the committee. LHC seems on track for start up in 2007. Some open questions related to the LEIR commissioning (lifetime, cooling, vertical chromaticity). FZ proposed an EPAC abstract for the HHH code repository. Y.-H. Chin, M. Giovannozzi, M. Furman, J. Qiang, L. Farvacque, J. Payet, D. Abell, F. Schmidt, R. Basset responded positively, many already providing additional information and adding new codes. FR suggested to contact A. Wagner regarding a different version of TRISIM. FR and FZ reported from the last LTC, with presentations by T. Linnecar on beam losses at injection energy in the SPS, by B. Dehning on beam-loss monitors, and R. Bailey on the organization of LHC commissioning. Schottky monitor signals show that parts of the beam close to the longitudinal center are lost. This may be consistent with the resonance-trapping model for the effect of the electron cloud, which would lead to transverse losses. FR recommended to simulate the Schottky scan using the HEADTAIL code. FR questioned the beam-loss simulations presented by BD, which show the losses concentrated at the entrance of the quadrupoles. FR recommend a cross-check with the collimation team. FZ asked whether the aperture changes at the quadrupoles are properly taken into account in the LHC impedance budget. ABP is heavily involved in the commissioning, with Oliver Bruning as a machine coordinator in parentheses, 5 out of 7 (8) commissioners in charge, and strong presence in the systems support teams. Posted on the web: Slides by DK Web site: http://ab-abp-rlc.web.cern.ch/ab-abp-rlc/