------------------------------------------------------------ Minutes of the ABP-RLC team meeting of 19.09.2006 present: OB, WH, EM, TP, GR, RT, FZ excused: FR web site: http://ab-abp-rlc.web.cern.ch/ab-abp-rlc/ ------------------------------------------------------------ (1) Reports from meetings & announcements ------------------------------------------ GR reported from the last APC meeting, which was devoted to the scrubbing run. Karel Cornelis gave an overview of the vacuum evolution. He concluded that the scrubbing run was too short this time. At the APC, Gianluigi Arduini commented that in his opinion there is no proof that the scrubbing run was too short. He mentioned that plenty of other problems badly affected the beam quality and the scrubbing efficiency. OB explained that there is a lot of pressure to meet the DG's schedule with the restart of LHC commissioning in April 2008. EM commented that the bunch length at injection into the SPS is shorter than before (3.7 ns full length compared to 4.2 ns in 2004), which could cause prolongated electron cloud. Another reason is the opening of large parts of the SPS ring during the shut down. The latter will repeat in each of the coming years. GR next reported that EB presented beam data collected during the scrubbing run. The e-cloud detector in a field-free region shows a rapid decay of the cloud after injection, but little change in behavior between the start and end of the scrubbing run. FZ analyzed BPM data. He found that the first bunches were horizontally far offset (up to ~10 mm) but that this offset was reproducible for successive injections. Changes can be observed on a day-to-day basis. For one set of data, the bunch-by-bunch positions on the 1st turn were non-reproducible in the vertical plane. In all other cases, the vertical position was stable and close to zero, without any bunch-to-bunch shifts. EM commented that the PS sees signs of an x & y instability which could be due to electron cloud. One problem is the lack of chromaticity control. The measured "matrices" which worked in the past, no longer function, The theoretical model, which did not work in the past, now seems to give better results. The matrices are being re-measured for the present PS. EM recalled that in 2001 e-cloud was observed in the PS, but at the time it occurred only on the last turns before extraction after bunch rotation and it had no effect on the quality of the extracted beam. However, it had been found that a coasting beam with 10-ns bunch length was unstable. The full bunch length before rotation used to be 16 ns, and now it is only 12 ns, which might explain why e-cloud could be more severe and set in long before the rotation. OB commented that scrubbing should be done at the expense of the CNGS beam since it is not needed for LHC commissioning. FZ added that at the APC Enrique Giaxola presented the results on kicker heating observed during the scrubbing run. This time, the heating was not limiting the scrubbing, as had been the case before. One reason is that the vacuum was much worse this year, and the other is the successful coating of the most sensitive kickers, which reduced their temperature increase by about a factor of 2. Gianluigi commented that only the MKQH kicker and one magnet of the MKE kicker in LSS6 have been shielded: the first with ceramic and the last with interdigital conducting strips. These kickers constitute a small fraction of the overall number of kicker magnets (which fraction is being clarified between GA and EG). GA also added that in LSS6 we are able to run with one kicker magnet less because the kicker magnets have been terminated differently (shorted) allowing to double the kicke strength for the same PFN voltage. This is possible only in LSS6, where the constraints on rise and fall times are not as stringent as in LSS4. OB summarized news from the ABMB. One topic was the APC discussed above. All requests for technical students have passed. There will be two in ABP. Jean-Pierre Delahaye has been asked to formalize the FP7 proposals. The rules for non-resident allowances will be changed. The distance allowance will be abolished, and the non-resindence allowance will disappear after 4 years, instead of decreasing to 50% in 8 years. The LTC next week will address the issue of LARP collaboration (discussed below). OB also reported from the PAF/POFPA meeting, which looked at medium/long-term planning of CERN. Some leading physicists expressed frustration that neutrino physics had not been properly discussed. PAF/POFPA will organize a colloquium on neutrino physics at the end of the year. It was remarked that neutrinos are one of the most interesting areas in particle physics. (2) Open Actions ---------------- OLD ACTION: Follow-up with Brennan the TDI gap requirements (EM) DONE. The TDI is closed only at injection. For 7.5 sigma available machine aperture the gap is set to 6.8 sigma at intensities above 2e12 protons. => ACTION: Check with RA that this gap is compatible with collimation requirements and whether the TDI can be a secondary collimator (EM) OLD ACTION: Check that beam-induced heating of several kW is acceptable (EM) EM reported that the acceptable heat load is 20 kW. OLD ACTION: Clarify TDI operation mode with Brennan (EM) The TDI is closed for about 20 minutes, during the full injection process. OLD ACTION: Follow up no. of TDIs w/o ferrite and spares (EM) DONE. Three TDI in total. One being installed now. The next one, to be installed in spring 2007, will have ferrites. The last one is a spare which will replace the first one installed in the 2007/08 shutdown. FZ pointed out that the measured TDI transverse broadband impedance corresponds to between the full LHC impedance budget and twice the budget. OB and EM concluded that we have to ask for rf fingers to be added in the final versions of the TSI which will be in the machine at high intensity. => ACTION: bring up this topic in the next ABMB (OB) => ACTION: beforehand inform Brennan with cc to Fritz and Tom (EM) (3) RW Benchmark with GSI calculation for SIS (EM) -------------------------------------------------- A new result sent by Rainer Hasse for the SIS RW impedance agrees perfectly with EM's result, both for the real and the imaginary part. The parameters represent the thin-wall regime. EM stressed that the LHC collimator case, where 4 orders of magnitude difference persists, does not belong to the same regime. (4) Crossing transition with TMCI (EM) -------------------------------------- Triggered by an earlier discussion at the APC, EM calculated how the chromaticity should be changed on the ramp in order to maintain a constant level of beam stability. In the PS a gamma_t jump is applied. The jump might be too fast to be followed with the sextupole strengths. (5) Review of theories for Landau-damping with space charge and nonlinearities (EM) ----------------------------------------------------------------------------------- EM summarized the historical evolution and characterized the main features of different theories of Landau damping. He pointed out that Alex Chao's book assumes an external frequency distribution, which is not correct if the frequency spread is in the plane of the coherent oscillation. Hereward had a more general treatment, in which the derivative of the distribution function enters. In the so-called Hereward-Laclare treatment the space-charge is introduced adhoc, which is not correct. The correct treatment is the one from Mohl and Schonauer. Berg-Ruggiero derived the same relations for octupoles only in a mathematically rigorous approach from the Vlasov equations. EM and FR finally gave the solution for the case of nonlinear space charge, with some assumptions. FZ remarked that at HB2006 a comment was made that the most refined theory available is the one from Mike Blaskiewicz, and that the latter might possibly be in better agreement with PATRIC simulations than the Mohl-Schonauer equations. EM received a comment from Bill NG, who could reproduce all equations and plots except for the first bump of the stability diagram in the case where tune shift and octupolar detuning have opposite signs. FZ asked for the physical significance of a curve in the negative imaginary plane. OB commented that such parts of the diagram do not make much sense, since the corresponding motion is always damped. (6) Preparation of meeting on LARP discussion (OB) -------------------------------------------------- OB explained the context. Hermann Schmickler will attend the US LARP meeting in October. He wants to make sure that the LARP money is spent in the way we want it to be spent. An example for what we are not interested in is the LER workshop at CERN. Another example how things can be changed is the demise of Nikolai Mokhov from LHC collimation studies. The FLUKA team took over these calculations. EM mentioned that Milorad Popovic is visiting CERN in the frame of US LARP for 2 weeks. He will work on the PS. OB will organize a pre-discussion meeting with Hermann some time this week, most likely on Friday. Everybody working with the US LARP should be prepared and/or send an assessment to OB. (7) Computing resources (OB) ---------------------------- Last week there was no tracking on lxplus due to problems with castor back up. OB highlighted that this vividly illustrates that the computer support is not God given. After major investments in lxplus this is an unpleasant situation. We need to prepare ourselves and compile reasons why lxplus LHC tracking studies are required until 2008 and beyond. The proposed alternative BOINC system was also interrupted last week. In the future it will be taken care of by Queen Mary College London. CPSS is the same as BOING but a system internal to CERN. It is in an undefined state. (8) Code repository (FZ) ------------------------ FZ illustrated novel features of the CARE-HHH code web repository, http://oraweb.cern.ch:9000/pls/hhh/code_website.startup which to a large extent were added by the summer student Cecile Lapoire. The innovations include an improved layout, new categories, additional codes, tables, and benchmarking support pages. FZ showed space charge and e-cloud as examples. OB commented that a new code G4beamline for loss studies could be included. This code was proposed by Roland Garoby as an alternative to FLUKA. A look at the "muons incorporated" web site http://www.muonsinc.com/programs/g4beamline.html reveals that the code is said to be a "Swiss army knife" for Geant4 and that it was written by Tom Roberts at FNAL. => ACTION: send code questionnaire to Tom Roberts (FZ) (9) Beam parameters for LHC upgrade (FZ) ---------------------------------------- FZ presented a list of possible LHC upgrade parameters, including a scenario with 25-ns spacing and 3.4e11 protons/bunch with larger transverse emittance. He created sample parameters sets for the PS2, PS+, SPS and SPS+ (see http://care-hhh.web.cern.ch/CARE-HHH/LUMI-06/default.html ), which will be discussed in a meeting organized by Michael Benedikt on Thursday morning. (10) AOB -------- RLC team members are asked to send information about their activity to Werner, in preparation for the group meeting. Posted on the web: Slides by EM Web site: http://ab-abp-rlc.web.cern.ch/ab-abp-rlc/