----------------------------------------------------------- Minutes of the ABP-RLC team meeting of 07.07.2006 present: OB, UD, DK, EM, WH, TP, GR, RT, FZ excused: FR web site: http://ab-abp-rlc.web.cern.ch/ab-abp-rlc/ ------------------------------------------------------------ (1) Follow Up of Actions from Previous Meeting ---------------------------------------------- In the previous meeting Ernst Radermacher, assisted by Fritz Caspers, had asked whether the copper coating of the Roman Pots can be dropped. Since the Roman pots are closed only with low-intensity beam, the change of impedance will not be an issue. FZ mentioned that electron cloud effects may occur with Roman pots closed and/or open, if the uncoated material has a high secondary emission yield (material not known at the time of the meeting) but since this would occur only over a limited region it would not compromise beam stability. A green light was given to the proposed change. (2) Reports from Meetings ------------------------- ABMB (OB): Resource problem for vacuum support. Only 4 PS magnets can be exchanged next shut down instead of the 8 planned. Support for CTF-3 is also problematic due to shift in operation schedule. CERN staff should be reduced to less than 2000 by 2010. AT is mainly affected. Vacuum group will suffer 48% reduction. 28% reduction foreseen in ABP group. Retiring staff will no longer be replaced. LTC (WH): Discussion of collision run at 450 GeV; RLC team is asked whether any problem is expected with regard to collective effects This is not the case. (OB): Paul Cruikshank reported on carbon-fibre cryosorber material which is sticking 0.5-1.0 mm far into the beam pipe after a mistake in processing. The aperture reduction is acceptable according to Bernard. APC (GR): Discussion on alternative scenarios of LHC filling in case the PS rotating machine breaks again. Three alternatives were considered: injection into the SPS at 26 GeV/c (longer cycle), 14 GeV/s or 20 GeV/c. Most favored is 26 GeV/c. The second best would be 14 GeV/c, which involves transition crossing. Studies on beam stability and electron cloud would be needed. Reports by GA, Michel Martini, EM, ES, and FZ . LHCCWG (FZ): Discussion of new 2007 schedule and outlook to 2008. 2008 schedule on hardware and beam commissioning already very tight. Physics run would start in the summer. Presentations by Roger Bailey and Roberto Saban. Also report by Jorg Wenninger on orbit response measurements in the LHC, with examples from transfer line commissioning and SPS. Scrubbing Mtg (GR): SPS scrubbing run will take place starting 17 July. Planning meeting was organized by GA. Lifetime, emittance growth, tune shift, profile, and e-cloud signal measured in regular intervals to monitor progress of conditioning and look for possible correlation of poor beam lifetime with electron cloud. (3) Other Short Communications ------------------------------ a) RW Impedance of LHC Collimator - GSI Result EM reported on an EPAC'06 paper on the resistive-wall impedance from the GSI team. Rainer Hasse, Al-Khateeb et al here computed the LHC collimator impedance. Their result dramatically differs from our impedance model: (1) the imaginary part also goes to zero at low frequency instead of approaching a large constant finite value; (2) The peak value of the impedance is found at about the same frequency but is about 50 times lower in magnitude; (3) at high frequency the imaginary part of the impedance goes against a constant, instead of decreasing. If the GSI result is correct, it would change all our conclusions on LHC collimator impedance. FZ remarked that the GSI model should be applied to the SPS collimator tests and compared with the experimental data. Since our model agrees within a factor of two or exactly (depending on whether Piwinski correction is taken into account), the GSI result is very likely to be inconsistent with the experiment, especially in view of the different peak value and the completely different behavior at higher frequencies. There is no derivation in the published paper. => ACTION => EM follow up of GSI result. b) Stability Diagram with Pinched Electron Cloud ------------------------------------------------ FZ presented a first attempt to compute the Landau damping and stability diagram from the frequency spread induced by the pinched electron cloud, with varying tune shift along the bunch. Considering a quasi-parabolic profile and a linearly increasing tune shift and proceeding in analogy to Hereward, Mohl-Schonauer, Chao and Metral-Ruggiero, he obtained a non-trivial result without any external nonlinearity, in contrast to the know space-charge case. He expressed concern that the result may violate momentum conversation. There was some discussion by EM and FZ on the differences or similarities between Hereward and Mohl-Schonauer, i.e., whether they disagree or whether Hereward did not study the same case. FZ mentioned that he could not find the 1969 paper of Hereward quoted by Kornilov. => ACTION => Clarify differences in dispersion relations? (EM?) FZ mentioned that he presented two new results on the scaling of the e-cloud TMCI threshold with beam energy at the last APC. c) Impressions from EPAC ------------------------ TP - Most impressive was the talk by Roger Penrose; Contacts were established with several groups working on beam-beam. An attempt will be made to simulate RHIC experiments with the CERN codes, e.g., COMBI; TP will profit from the presence of Rama Calaga at CERN. Tevatron will soon take data with turn-by-turn bunch-by-bunch position measurements. This will allow comparison with strong-strong simulations; FNAL contact is V. Lebedev. GR - e-cloud is finally observed in DAFNE, limiting the performance. Emittance growth seen in RHIC polarized p run could be due to e-cloud; contact is W. Fischer. Talk on modelling of e-cloud instability failed to address the topic. RT - impressive general trend to refined BPM spectral analysis, e.g. for coupling correction at FNAL, RHIC and new light sources; two weeks commissioning of SOLEIL. UD - beam wire compensation reported to be successful at DAFNE; lifetime is significantly improved; doubts in DAFNE simulations: - based on mad8 (insufficient precision); weak dependence on wire current; large ~30 degree phase advance between important parasitic collisions and wire; UD will receive a DAFNE MAD-X file from Catia Milardi soon. WH suggested including radiation damping in the DAFNE simulations. d) HHH Summer Student --------------------- FZ reported that a HHH summer student, Cecile Lapoire has started this week. Her tasks are to update the code repository, to help setting up the code benchmarking, and possibly to modify the dynamically created web pages (or copying these pages into a static version). The last task implies getting familiar with ORACLE and SQL, which may be challenging. OB and WH offered some introductory ORACLE tutorial material for CL. Posted on the web: Slides by EM and FZ Web site: http://ab-abp-rlc.web.cern.ch/ab-abp-rlc/