------------------------------------------------------------ Minutes of the ABP-RLC section meeting of 05.12.2006 present: OB, FC, UD, WH, JJ, EM, FRo, GR, BS, FZ excused: FR web site: http://ab-abp-rlc.web.cern.ch/ab-abp-rlc/ ------------------------------------------------------------ (1) Report from Meetings ------------------------ LHCCWG (FZ) The squeeze was discussed with 3 presentations, by M. Giovannozzi on optics, R. Assmann on collimation, and M. Lamont on software implementation, sequencer and power converter tests. ABMB (OB) 7 PAC participants from ABP were approved, 3 of which from EUROTeV, plus 2 out of quota. The deadline for PAC abstract submission is middle of next week. Any abstracts should first be sent to OB prior to the official submission. PAF (OB) Malika Meddahi joined for the 1st time as secretary. PS2 (JJ) Discussions on more optics solutions, space-charge compensation with e-lens, and PS2 rf systems. LCWG (EM) First results of collimator impedance measurements in 2006; including instability growth rates. (2) Informal meeting on incoherent e-cloud effects (GR) ------------------------------------------------------- EB, WB, GR, DS, and FZ participated. Features and merits of different codes were reviewed. HEADTAIL code: one IP excites all resonances; frozen field approximation is implemented; uses e-cloud distribution from ECLOUD. MICROMAP: refined lattice model; correct resonance lines are excited; but rough model of bunch/e-cloud interaction; need to improve the pinch model in MICROMAP; always frozen field approximation; Faktor2: so far ion and electron build-up code; arbitrary 2d arbitrary boundary conditions; fine meshing; ideal for modeling grooved surfaces and clearing electrodes; presently being extended to 3D code, which needs many days of computing time; action of e-cloud back on the bunch so far not included; missing is a macroparticle model for the bunch and beam propagation. Different proposals were made: FZ: import MICROMAP to CERN DS: improvement in HEADTAIL code by some clever way so as to reduce the number of kicks to be applied while preserving the resonance strengths; EB: upgrade of HEADTAIL, and/or inclusion of e-cloud module in MAD-X It was noted that MICROMAP was benchmarked against HEADTAIL. The emittance growth agreed within a factor of two or better, depending on the pinch model. What actually is our goal? FZ suggested that a reasonable goal is to predict emittance growth in the LHC. WH commented that emittance growth has never been successfully predicted. OB proposed as the goal and conclusion: - estimate of emittance growth rate in LHC - who does this depends on the road we take (or vice versa) In view of lacking resources in ABP, FZ suggested that we could try to involve US-LARP in this effort. A possible candidate may be Mauro Pivi, who is already using an incoherent code MAD_CLOUD, based on mad8, at SLAC. Another possibility could be help from Theo Demma (U. Sannio), who would like to visit for a couple of weeks next year. EM recalled the space-charge benchmarking of MICROMAP which he had done at the PS, where simulations were in good agreement with measurements. He presented slides from his talk in Senegalia, where 2 measurement campaigns were discussed which successfully validated the beam loss and emittance growh mechanism proposed by G. Franchetti and I. Hofmann. Namely, depending on location of resonance line with respect to tune necktie one can find either a regime of loss-free core-emittance growth or a regime where continuous loss occurs. This result was published PRST-AB 6, ... (2003) The emittance growth and beam loss measured when lowering the working point towards the resonance emittance growth were in good agreement with simulations. WH asked how good the agreement actually was. This will be discussed in a future meeting. FZ commented that the agreement was continually improved from month to month, by G. Franchetti, who added more and more features to the model, and the latest simulations differ from the experimental data at the level of 10-20%. => ACTION => examples for agreement between G. Franchetti's simulations and PS measurements of emittance growth and beam loss (EM, FZ) EM recalled the similarity of these observations with the beam losses seen in the SPS, which had given rise to his idea that a similar effect could be at work in the SPS. => ACTION => OB will talk to Wolfram on US-LARP activities, and possibility of Mauro contributing to incoherent e-cloud studies and MAD-X module; => ACTION => FZ will discuss with Frank Schmidt; perhaps Frank Schmidt has other contacts who can help (e.g., in other sections). (3) Report from LNF Scientific Committee (JJ) --------------------------------------------- DAFNE has been dramatically modified: change of detector - Finuda moved in; clearing electrodes were removed; collisions since 4th of November; 5% reduced wiggler field; optimization in various regards; e+ current limited by fast x instability to 0.5 A (0.7 A), ~two times lower than in previous years; instability nature not understood; some speculation that it could be electron cloud; the instability depends on the orbit in the wiggler; similar effects is said to be seen in the e- ring, which is not current limited; HOM in wiggler chamber could be another explanation; no consensus on the cause yet; parasitic beam-beam effects from second IP reduced by lowering beta there; luminosity of 0.6e32 reached so far in this run (1.3e32 previously with KLOE); goal is an integrated luminosity of 1 fb-1 by April next year; 0.6-0.8 are expected at the present rate; the run may be extended by a few months; now still vacuum conditioning (90/110 bunches at present). Plan of luminosity upgrade with crabbed waist to get above 1e33; simple IP with large crossing angle; modified wigglers, symmetric with respect to the orbit; cheap upgrade scheme. Crabbed waist will be operational together with Siddharta; results on the scheme's benefit expected by early 2008. Basis of new approach to energy upgrade instead of DANAE. SPARC FEL start up: good understanding of beam dynamics, found in good agreement with simulations. All LNF SC talks can be seen on the web site http://www.lnf.infn.it/committee/33opensc.html (4) AOB ------- In view of the ABP Christmas party, there will be no further section meeting before the end of the year. Posted on the web: Slides by GR Web site: http://ab-abp-rlc.web.cern.ch/ab-abp-rlc/