Minutes of the ICE section
21th meeting on Wednesday 23/03/2011 (08:40-10:30, 6/2-004)
ICE members: Benoit Salvant (BS), Christian Hansen (CH), Carlo Zannini (CZ), Hugo Alistair Day (HD), Elena Benedetto (EB), Ewen Hamish Maclean (EHM), Elias Metral (EM), Elena Wildner (EW), Frank Schmidt (FS), Giovanni Rumolo (GR), Jean-Luc Nougaret (JLN), Kevin Shing Bruce Li (KL), Maria Carmen Alabau Pons (MCAP), Nicolo Biancacci (NB), Nicolas Mounet (NM), Olav Ejner Berrig (OB), Tatiana Pieloni (TP), Werner Herr (WH).
Present/Excused: BS, CH, CZ, HD, EB, EHM, EM, EW, FS, GR, JLN, KL, MCAP, NB, NM, OB, TP, WH, Alessandro Vivoli, Fritz Caspers, Hannes Bartosik, Javier Cardona, Rama Calaga.
1) Newcomers / visitors
- Javier Fernando Cardona from Universidad Nacional de Colombia, Bogota (JFcardona@unal.edu.co or Javier.Cardona@cern.ch) will be at CERN from 14/03/11 to 04/06/11, working on optics with RogelioT.
2) Comments on the minutes of the 20th meeting + Actions
- No comments.
- List of Actions => Discussed in detail later.
3) General infos
- No particular comment from anyone.
- SL meeting last week:
- Nothing particular to mention.
- News on the LHC:
- 08:30 meeting on Monday 21/03/11:
- 21:30 on SU 20/03 => 1st fill of stable beams with 136 bunches (good lifetimes).
- Some vacuum activity was observed and is followed up. It seems that the solenoid was OFF for ATLAS and ON for the 3 other experiments.
- The intensity per bunch over the week was very stable between 1.1E11 p/b and 1.2E11 p/b, and same thing for the (computed from the initial peak luminosity) transverse emittances: slightly above ~ 2.5 microm (with ~ 2 microm measured at injection).
- Yesterday's fill (with 136 bunches) => Slightly more than 1.6E32 cm-2s-1, i.e. close to last year's luminosity record (~ 2.07E32 cm-2s-1).
- Yesterday's night (i.e. on 22/03/2011) fill (with 200 bunches) => ~ 2.5E32 cm-2s-1, i.e. more than last year record (~ 2.07E32 cm-2s-1)! Note that the record last year was obtained with 348 colliding bunches.
- SPS => Work of NM for the RW instability of the SPS and the comparison between SB and CB instabilities etc. (after some discussions with GR of SB instability studies made in the past) => Nice non-monotonic plot of instability rise-time vs. intensity for negative chromaticity done last year by BS, which still needs some thinking to fully understand what happens (see http://Paf-spsu.web.cern.ch/paf-spsu/meetings/2010/m25-03/TMCIIntensityThresholdForLHCBunchesInTheSPS.ppt, page 28): effect of quadrupolar impedances, mode coupling, etc.? Action1: HTWG. Idea from ElenaS to measure and simulate the case of batches of 72 bunches spaced symmetrically in the SPS to avoid ecloud and then put them closer and closer to see the effect on the coupled-bunch instabilities => May be with this method we could disentangle the contributions from impedance and ecloud. To be followed up.
- Email from OliverBF (on 16/03/2011) for the visit at CERN of Vladimir Kornilov => We said yes for 1 or 2 weeks in May in the past (exact dates still to be found by Giovanni) and GSI will pay for the trip and CERN for part of the accommodation. Action2: EM to check what we can do.
- Shields in the SPS => Email from GA after discussions in the SPSU etc.: the idea is to insert a shield, which is coated with carbon instead of coating the chamber itself (for the half of dipoles whose aperture is less a problem in the SPS). Action3: Impedance team to follow this activity as Mauro Taborelli will come with some questions at some point (after the proper choice of material/thickness etc. to avoid Eddy currents etc.) + send to Mauro the formula for the power loss. Action5: OB to check the maximum aperture we could remove in ~ half of the dipoles.
- Info from J.L. Nougaret (for the ZBASE activity): It is not clear yet when he will be back.
- Reminder on the info I sent for the OPTICS studies: Please check with / inform Massimo for all the MDs you would like to do in the LHC, which are related to OPTICS as it has to be added to the whole list of optics studies. This is important to avoid duplication and in particular when priorities will be discussed.
- SPS BPM studies: BS presented an update on BPM impedance in the SPS at the last SPSU. Action 6: BS (impedance team) check why the resonance at ~ 2 GHz, above cut-off according to FC, has such a high Q, which would mean that the mode does not couple to boundaries etc (to be checked by changing the boundaries). Action 7: Impedance team to answer to a request from ElenaS in ~ 1-2 months: Study the SPS BPM enameld flanges(all, i.e. ~ 200, SPS BPMs are electrically isolated by enamel flanges (one in each side) => We could also contact Yoshihiro Shobuda (shobuda@post.kek.jp), who developed a 3D analytical model for small gaps, to compare with our simulations.
- Reminder on the deadline (from Marc Timmins) for the DS collimators: The deadline for providing all the manufacturing drawings to the main workshop is end of April. So the models will be frozen at the latest at that time (Action 8 for the impedance team).
- LHC scrubbing run:
- It is foreseen for the end of next week => GianluigiA will certainly organise a meeting and disucss it at the next LBOC.
- We will try and summarize what we measured last year and what we learned from the several months of simulations/studies before the scrubbing run (end of next week and beginning of next one).
- Beam-beam:
- GianluigiA mentioned that the 1st bunch of the trains with 75 ns bunch spacing (24 bunches) is always smaller in bunch intensity (~ 10%). It seems it is known (from Steve Hancock) and due to beam loading in the RF cavities => We should try and check what the bunch lifetime is for this low intensity bunch.
- Reminder on the info I sent you on Induction Interview for Fellow: new EDH document => https://edh.cern.ch/Document/Personnel/InductionFellows. In this new document, the supervisor should write the objectives (work and training) to be reached by the fellow during the first year following an induction interview, which is highly recommended and which should take place within the first 6 weeks after the start of the contract. Link to the Induction Programme = https://admin-eguide.web.cern.ch/admin-eguide/formalites/proc_induction.asp.
- Discussions at the beginning of the meeting with Rama on the impedances of taper IN and OUT etc. => Would be good at some point to review this subject as there were many formulae circulating in the past for different regimes, with some confusion. To be followed up in the impedance team (Action 8).
- Approved ICE participation to IPAC2011: WH and GR. The other people from the ABP group are: Gianluigi Arduini, Oliver Bruning, Frank Zimmermann, Richard Scrivens, Ralph Wolfgang Assmann, Laurent Deniau, Helene Mainaud Durand, John Jowett, Daniel Schulte, Roderik Bruce, Piotr Krzysztof Skowronski, Stephan Maury, Jochem Snuverink, Piero Antonio Posocco, Simone Gilardoni. Action 9: All the ICE members (who want to present a paper and have someone to present the results there) to send the abstracts to Oliver Bruning and myself on Monday 4 April 2011 at the latest (the deadline for abstract submission is 13 April 2011, but the abstract must firstly be approved by our group leader (+ project leader if necessary) and then one should send it to Anna Mackney by Thursday 7 April for approval by the Department Head ).
4) Status of the list of Actions
- We reviewed it altogether.
5) 1st LHC beam-beam observations in 2011 (TP) => POSTPONED TO THE NEXT MEETING
6) General wall impedance theory for 2D axisymmetric and flat multilayer structures: Part II (NM): ppt (the last week talk was slightly updated)
- See summary of last week => http://emetral.web.cern.ch/emetral/ICEsection/2011-03-16/ICE%20Min%20meeting_16-03-11.htm.
- NM added some formulae (page 13 for instance) as discussed during last week meeting.
- NM discussed in some detail the longitudinal impedance at low frequencies (FritzC's comments) and high frequencies, where the impedance tends to 0 in both cases. For high frequencies, this is due to the fact that there is no more induced currents in the wall because the EM fields from the beam (=direct space-charge, i.e. the fields present if no boundary was there) decays before reaching the wall (=> due to the finite gamma).
- NM explained in some detail the flat case, where a similar approach is used, replacing the discrete decomposition and sum (due to the 2 Pi periodicity of the azimuthal angle) by a continous decomposition and integral (in Cartesian coordinates instead of Cylindrical ones).
- FritzC made a comment about the ansatz of the separation of variables, which assumes orthogonality and therefore prevent coupling between longitudinal and radial which might occur in some cases => To be followed up.
7) Review of Hamiltonian treatment of synchro-betatron motion: Part I (KL) => POSTPONED TO THE NEXT MEETING
8) Actions to be taken for the next meeting
- Old actions.
- New actions:
- Action 1 (HTWG): Check that idea from ElenaS to measure and simulate the case of batches of 72 bunches spaced symmetrically in the SPS to avoid ecloud and then put them closer and closer to see the effect on the coupled-bunch instabilities => May be with this method we could disentangle the contributions from impedance and ecloud. To be followed up.
- Action 2 (EM): To check what we can do for the visit from Vladimir Kornilov (GSI).
- Action 3 (impedance team): Discussions to insert a shield in the SPS, which is coated with carbon instead of coating the chamber itself (for the half of dipoles whose aperture is less a problem in the SPS) => Follow this activity as Mauro Taborelli will come with some questions at some point (after the proper choice of material/thickness etc. to avoid Eddy currents etc.) + Send to Mauro the formula for the power loss.
- Action 4 (OB): For the previous idea discussed in Action 31, check the maximum aperture we could remove in ~ half of the dipoles, to give a value to Mauro Taborelli.
- Action 5 (impedance team): BS presented an update on BPM impedance in the SPS at the last SPSU => Check why the resonance at ~ 2 GHz, above cut-off according to FritzC, has such a high Q, which would mean that the mode does not couple to boundaries etc (to be checked by changing the boundaries).
- Action 6 (impedance team): Try and answer to a request from ElenaS in ~ 1-2 months: Study the SPS BPM enameld flanges(all, i.e. ~ 200, SPS BPMs are electrically isolated by enamel flanges (one in each side) => We could also contact Yoshihiro Shobuda (shobuda@post.kek.jp), who developed a 3D analytical model for small gaps, to compare with our simulations.
- Action 7 (impedance team): The deadline (from Marc Timmins) for providing all the manufacturing drawings for the DS collimators to the main workshop is end of April. So the models will be frozen at the latest at that time.
- Action 8 (impedance team): Review of the impedances of tapers (IN and OUT).
- Action 9: All the ICE members (who want to present a paper and have someone to present the results there) to send the abstracts to Oliver Bruning and EM on Monday 4 April 2011 at the latest.
9) Miscellaneous
- The next (22th) meeting will take place on 30/03/2011 => Agenda:
1) Review of Hamiltonian treatment of synchro-betatron motion: Part I (KL)
2) 1st LHC beam-beam observations in 2011 (TP)
- See preliminary agendas for the next meetings.
Minutes by E. Metral, 24/03/2011.