From: "Werner Herr" To: "Francesco Ruggiero" Cc: "Bruno Zotter" ; "Daniel Schulte" ; "Elias Metral" ; "Frank Schmidt" ; "Frank Zimmermann" ; "Gianluigi Arduini" ; "Helmut Burkhardt" ; "Hiroshi Tsutsui" ; "John Jowett" ; "Robert Gluckstern" ; "Werner Herr" ; "Luc Vos" ; "Maxim Korostelev" ; "Alex Koschik" ; "Eric D'Amico" ; "Walter Wittmer" ; "Gregory Penn" ; "Lifshitz Ronen" ; "Elena Benedetto" ; "Jean-Pierre Riunaud" ; "Karlheinz Schindl" ; "Louis Rinolfi" ; "Michel Martini" ; "Oliver Bruning" ; "Roberto Cappi" ; "Charles Hill" Subject: Re: LCE team meeting next Friday 20 June Date: Friday, June 20, 2003 9:09 AM Summary of the BISpeC WG meeting of the 18th June 2003 Present: O. Bruning, C. Fischer, R. Schmidt, J.P. Koutchouk, Invited for topic 1: H. Schmickler, W. Herr, F. Schmidt, A. Burns, W. Hofle, L. Ducimetiere, S. Fartoukh Excused: J.J. Gras, J. Wenninger. 1. Beam excitors The two classes of beam excitors, kickers and shakers were considered separately: a. Kickers Q-kickers: The Q-kickers foreseen allow kicking the beam to 2.6 sigma at 450 GeV and 0.7 sigma at 7 TeV. This is fine for Q-measurement but insufficient for non-linear studies. Aperture Kickers for 450 GeV: The aperture kicker (8 sigma) is felt mandatory at injection. Indeed the machine performance limit at 450 GeV is a single particle issue. Furthermore the non-linearity is distributed. In thiese conditions, the kick-methods are most appropriate. This functionality is presently provided by the aperture kicker (8 sigma at 7 TeV, 32 sigma at 450 GeV). Aperture Kickers for 7 TeV: At 7 TeV on the contrary, the non-linearity is localized in the triplets and IR’s. It can be reduced to an insignificant level by optics detuning and the choice of the beam current (long-range beam-beam effect) at the expense of a lower performance. The localized non-linearity can be studied by several methods (e.g. bump method demonstrated in RHIC). The kick method involves kicking the pilot beam to about 8 sigma. This should be safe with collimators withdrawn but limiting the aperture (R. Assmann). The safety margin is however only 2 sigma beyond which the damage limit is approached or reached. Discussion: The consensus is that aperture kicking at 450 GeV is mandatory while it should be an open option at 7 TeV, to be decided soon after the LHC commissioning. A one year notice (Laurent) is required to build and install the required power generator. This is felt acceptable. If the option was abandoned today, the savings in kicker hardware would be insignificant. It is therefore agreed to cancel the request for a 7TeV aperture kicker power generator and to keep the kicker hardware compatible with an upgrade. The aperture kicker at injection remains a requirement which can no longer be fulfilled using the former option. The use of the dump kicker is totally excluded for safety reasons. The use of the injection kicker could be contemplated, but it would requiredan increased complexity in interlocks and kick in only the vertical plane. It is agreed to boost the power generator of the Q-kicker to produce 8 sigma oscillations at 450 GeV (2 sigma at 7 TeV). This can be done technically with a very small cost increase. The drawbacks were discussed and accepted: 1. ¼ (instead of 1/12) of the bunches will be kicked simultaneously: this does not change the situation when debugging the machine with one or a few bunches. Furthermore, a factor of 2 or more in bunch selectivity may be gained by shifting properly the timing (Stephane) at the expense of a larger emittance blow-up for the bunches kicked several times. At injection, the damper may be used in few turns to kick only few bunches at about 1 sigma (2 urad per turn at 450 GeV, Wolfgang). Finally, the kick method is to be used only until the PLL is operational (Hermann). 2. Repetition rate: to be clarified (Alan looking into it) 3. The hazards to the machine are increased but the oscillation amplitude at 7 TeV remains small (2 sigma). Interlocks based on beam current should be provided to limit the kicker charge. Rudiger will investigate the situation which looks, a priori, OK. The cost saving should be invested in R&D on an AC dipole (frequency outside beam eigen-frequencies) which would be the ideal safe excitation means in LHC if it can produce large enough amplitudes. A new specification for the Q-kicker summarizing the above-mentioned changes will be written by Alan and sent to Rudiger for MP analysis. The goal is to finalize by Email within 3 weeks to present the conclusion to LTC on the 9th July. b) Shakers Interpretation of the table: The oscillation amplitudes quoted are that needed at equilibrium. Stephane questions the tickler in bunch-by-bunch mode for the measurement of the beam-beam transfer function: the beam-beam coupling is weak and an excitation to only 0.1 sigma might be insufficient in bunch-by-bunch mode. This of course depends very much on the PU sensitivity. The issue is to be resolved but not for the baseline programme. Werner will investigate whether bunch-by-bunch excitation is useful for other purposes, e.g. study of coupling between bunches. Wolfgang says that the damper can easily produce a 0.1 sigma oscillation within its bandwidth at any energy. For the low amplitude envisaged, Wolfgang proposes the damper to be used as `tickler’ with a bunch-by-bunch selectivity. Hermann underlines that the advantage of the dedicated tickler is the ability to increase the frequency bandwidth beyond the 20 MHz of the damper. c) Other diagnostics of the Non-linearity Hermann suggest considering as well other means in measuring the non-linearity. Transverse profile monitors with a high dynamic range (10^5) could be used to study the tails. There is interest in such a device if it can be built. Stephane recalls that the bump method is best suited for the low-beta sections at 7 TeV. The method of blowing up the beam emittance gradually is well adapted to LHC as well (loss control). It was fully operational in the SPS. 2. Specification of the Beam Intensity Measurement The ion parameters are expected from J. Jowett very soon. 4.1 to 4.3: OK 4.4: the 1% resolution applies to all uses except lifetime. 4.5: it should be noted that the lifetime is `instantaneous’, i.e. that its equation does not assume necessarily an exponential decay. 4.5.1: There is probably a mis-understanding of JBJ’s table of lifetimes in the Beam loss spec. To be clarified by JPK. This would most likely make the CT’s useless for quench prevention. This is not an issue as the occurrence of a beam loss without information on its location, of the collimation status and efficiency, makes the interpretation of the CT information ambiguous. Nevertheless, RS proposes to consider as an option the possibility of using the loss rate for interlocks (e.g. for stopping some operation steps,…) 4.5.2: OK 4.5.3: depends on the interpretation of the beam loss table (see above). May have to be suppressed. Machine protection: RS wrote the corresponding section. The CT’s are asked to produce a reliable signal to allow high intensity injection in the form of a GO/NOGO signal from the CT’s. This comes in addition to the intensity interlocks needed for the screens, WS,…which have to be added. JP -- --- W. Herr, SL-Division, CERN, CH-1211 Geneva 23, Switzerland Tel. +41 22 767 4781, Fax. +41 22 767 8480, E-mail: Werner.Herr@cern.ch Internet: http://cern.ch/Werner.Herr/