Minutes of the ICE section
75th meeting on Wednesday 13/02/2013 (08:40-10:30, 6/2-004)
ICE members: Benoit Salvant (BS), Carlo Zannini (CZ), Danilo Banfi (DB), Daria Astapovych (DA), Hugo Alistair Day (HD), Elias Metral (EM), Elena Wildner (EW), Frank Schmidt (FS), Giovanni Iadarola (GI), Giovanni Rumolo (GR), Jean-Luc Nougaret (JLN), Kevin Shing Bruce Li (KL), Nicolo Biancacci (NB), Nicolas Mounet (NM), Olav Ejner Berrig (OB), Serena Persichelli (SP), Sergio Rioja Fuentelsaz (SRF), Tatiana Pieloni (TP), Werner Herr (WH), Xavier Buffat (XB).
Present/Excused: BS, CZ, DB, DA, HD, EM, EW, FS, GI, GR, JLN, KL, NB, NM, OB, SP, SRF, TP, WH, XB, Alessandro Vivoli, Alexander Molodozhentsev (from KEK), Alexej Grudiev, Alexey Burov (from FNAL), Andy Butterworth, Bettina Mikulec, Cedric Hernalsteens, Chandrashekhara Bhat (from FNAL), Christian Carli, Christine Vollinger, Daniel Valuch, Daniel Wollmann, Eirini Koukovini Platia, Elena Shaposhnikova, Fanouria Antoniou, Frank Zimmermann, Fritz Caspers, Gabriel Mueller, Gerad Tranquille, Gersende Prior, Giulia Papotti, Giuliano Franchetti (from GSI), Georges Trad, Hannes Bartosik, Harry Renshall, Haryo Sumowidagdo, Helmut Burkhardt, Humberto Maury Cuna, Javier Fernando Cardona, Ji Qiang (from LBNL), John Jowett, Kazuhito Ohmi (from KEK), Lajos Bojtar, Massimo Giovannozzi, Mathilde Favier, Michel Martini, Miriam Fiterrer, Octavio Dominguez Sanchez de la Blanca, Rama Calaga, Raymond Veness, Raymond Wasef, Riccardo de Maria, Roderik Bruce, Rogelio Tomas, Sandra Aumon, Simon White, Tatiana Libera Rijoff, Theodoros Argyropoulos, Tom Mertens, Uli Wienands (from SLAC), Valeri Lebedev (from FNAL), Vittorio Vaccaro (from Naples), Wolfgang Hofle, William Andreazza, Yannis Papaphilippou, Yuri Alexahin (from FNAL), Mauro Migliorati (from Rome, La Sapienza), Letizia Ventura, Michael Bodendorfer, Humberto Maury Cuna, Simone Gilardoni.
1) Newcomers / visitors
- Daria Astapovych started on 01/02/13 as oPAC (she will also do a PHD with Alexey Burov and EM on "Longitudinal-to-Transverse Landau Damping for HL-LHC") and Kevin Li as LD => Welcome and we are very pleased to have you in our team!
2) Comments on the minutes of the previous 74th meeting + Actions
- No comment.
3) General infos
- No particular comment.
- SL meeting:
- ABP group structure: Discussions ongoing but EM did not mention anything until now as there is no (major) change for ICE => Few people should join the team. Need also to discuss/clarify the the role, mandate and responsibilities of the different ICE working groups. These discussions were reported by EM in some detail at the beginning of this meeting. All comments and suggestions and more than welcome (please do not hesitate!).
- New document to be filled by the supervisor for any request of training language: http://emetral.web.cern.ch/emetral/SomeUsefulLinks/20130204%20BE%20Language%20Training%20-%20Supervisor%20Grids.docx. Note that in the case of the level 0 in English (for BE integration), the request should be sent directly to Eric Montesinos (i.e. without going througb EDH). Otherwise the table should be completed, signed by the supervisor and attached to the EDH request.
- Comments on the last HL-LHC PLC meeting: Crab cavities require the LLRF electronics at less than 40 m from the cavity. This might imply civil engineering work to provide the required space in the tunnel. The number of modules is still under discussion. The global optimisation of the layout should be started urgently.
- LIU-HL-LHC workshop: The need of the upgrades (injectors and LHC) will be re-discussed in ~ September.
- LHC Machine Protection (MPP) workshop, Annecy, 11-13/03/2013: https://indico.cern.ch/conferenceDisplay.py?ovw=True&confId=227895.
- Several MDs took place in the PSB and PS.
- Changes in LHC IR3 (Adriana Rossi) => The idea is to install a new passive absorber in front of Q5 and the main changes are the moving of the BPM from the Q5 towards D2, and a reduction in aperture on the beam lines of the absorber. The reduction seemed to be the most rational way of avoiding an "accordion" like beam pipe, and reduces to the minimum the RF transition. One of the transition in the BMPW is from 59/44 to 30/52, but this should already exists somewhere else in the machine.
- LHC beam stability diagnostics review after LS1 organised by RalphS on : https://indico.cern.ch/conferenceDisplay.py?confId=234589.
- SF stepped down as HL-LHC WP2 Task 2.4 leader and he will be replaced by GA after the steering committee on 14/02/13.
- EM and FritzC went to the Mini-workshop on "Simulation of Power Dissipation and Heating from Wake Losses in Accelerator Structures", Diamond Light Source, 30/01/2013 => http://www.diamond.ac.uk/Home/Events/Past_events/Simulation-of-Power-Dissipation---Heating-from-Wake-Losses.html.
- SAPPHIRE (Small Accelerator for Photon-Photon Higgs production using Recirculating Electrons) day on 19/02/13: https://indico.cern.ch/conferenceDisplay.py?confId=231263.
- TLEP3 day 4-5/04/13 => We need to make some estimates for the TMCI which was the limitation for LEP.
- From 21/02/2013 to 22/02/2013: Joint Snowmass-EuCARD/AccNet-HiLumi LHC workshop 'Frontier Capabilities for Hadron Colliders 2013', CERN (https://indico.cern.ch/conferenceDisplay.py?confId=223094).
4) E-cloud activities - 2012 achievements & plans for 2013 (FZ): pptx
- Several meetings in 2012, ECLOUD'12 workshop, ICAP'12 and IPAC'12, preparation for, participation in, and analysis of the 2012 scrubbing run.
- Main work:
- Analysis & benchmarking of 2011 & 2012 surface conditioning (heat load, vacuum, phase shift).
- PS studies: effect of bunch shape & bunch length.
- Numerous ECLOUD-PyECLOUD comparisons.
- Simulations for various LHC upgrade scenarios.
- Journal publications.
- GI studies LHC:
- Reproducing measured 2011 heat load by PyECLOUD simulations => Scrubbing in the arcs: deltamax decreased from 2.1 to 1.52 in the arcs.
- Comparing simulated and measured energy loss (from stable phase shift).
- HumbertoMC:
- Arc heat load vs. bunch spacing => Dramatic increase for bunch spacing < 10 ns spacing.
- Heat-load ration ECLOUD/PyECLOUD => ECLOUD heat-load smaller for small deltamax and Nb ~ 5E10 p/b.
- Arc heat-load in 2012 scrubbing => Arc SEY evolution during 25 ns scrubbing: ~ 5% decrease (starting at ~ 1.5-1.6).
- ChandraB:
- Comparison between ECLOUD and PyECLOUD simulations => Faster build-up and earlier saturation with ECLOUD.
- Inconsistency of photoelectrons in dipole field between ECLOUD and PyECLOUD (with HumbertoMC) => ECLOUD sees only ~ 40% of the photoelectrons. The difference in the photoelectrons between the 2 codes should be explored (Action 1 below). The large difference seems to indicate that the physics is not the same in the 2 codes, according to FZ. FZmentioned that there is a good reason why many photoelectrons are quickly lost in the presence of a dipole field (because they bounce back against the wall within one cyclotron period) as seen in ECLOUD. The fact that PyECLOUD does not show any such loss is a bit puzzling. The problem could also be in ECLOUD, but then we should understand the mechanism by which all the electrons survive.
- Landau cavity & e-cloud @ PS ejection => Experimental results similar to simulations predictions. Comparison between experiment data and simulations sets tight range on the SEY parameters: epsmax= 287 eV (±3%), deltamax =1.57 (±1%) and R0=0.55 (±3%) in region of PS e-cloud monitor.
- Average heatload for HL-LHC w Landau RF => ECLOUD and PyECLOUD results agree: Landau cavity will not suppress e-cloud build up in the LHC, but it will not make it worse.
- LHC heat load vs. bunch length => Bunch shortening (or bunch lengthening) needed during high bunch intensity operation for the HL-LHC using a Landau cavity has no impact on e-cloud growth.
- OctavioD:
- SEY in straight sections - pressure benchmarking => Clear reduction of deltamax according to observations.
- PyECLOUD vs. ECLOUD for benchmarking studies (test of sensitivity to number of macroparticles) => PyECLOUD seems to be more robust wrt number of macroparticles and other parameters explored such as grid size.
- Ecloud maps (to reduce the computing time by ~ 7 orders of magnitude) => Suggested filling schemes fro scrubbing.
- ECLOUD vs. PyECLOUD: According to GI the physics is the same in both codes as he implemented the same equations => Differences could/should only come from numerical issues and we need therefore to check the convergence very carefully.
- ECLOUD'12 workshop:
- WARP-POSINT code at LBNL from J.L. Vay => Can simulate the whole SPS for build-up and instability.
- ICAP'12 workshop.
- 2 papers in PRSTAB for LHC and HL-LHC.
- Ongoing effort and plans for 2013:
- e-cloud simulations for extremely short bunch spacings in HL-LHC (proposal by S. Fartoukh): 5 ns, 2.5 ns, 1.25 ns (OctavioD).
- e-cloud for HE-LHC and VHE-LHC (OctavioD).
- 3D photon simulations for LHC, HL-LHC, (V)HE-LHC (HumbertoMC, visit to Cornell last week)
- StephaneF's scenario: average intensity is constant.
- It is better to go to very short spacing and the enegry gain is 0.
- Parameters list for LHC, HL-LHC, HE-LHC, VHE-LHC.
- OctavioD:
- HL-LHC studies => Stripes at 25 ns - 7 TeV (and 5 ns - 450 GeV and 2.5 ns - 450 GeV) and deltamax = 1.05. Comment from SimoneG: with the 5 ns we could scrub more but the stripes are not at the good place but we could move the beam.
- HE-LHC studies.
- Soon, VHE-LHC: a 50 ns beam at 50 TeV!
- HumbertoMC => Future work on LHC photon map:
- Synrad3D developed at Cornell (for Cesr-TA) by David Sagan and Gerry Dugan (seems very similar to PHOTON code written by FZ).
- Modifications for LHC already made and the code is ready to simulate LHC-like machines.
- Good luck to OctavioD and HumbertoMC for the finalization of their PHD theses by late summer 2013!
- Comment from W. Herr that for the pile-up what is important is the total number of events IN the detector.
- 50 ns is no pb for ecloud for HE-LHC.
- One could have TLEP and then VHE-LHC.
- Comment and suggestion from AlexeyB:
- When he is looking to the understanding of the LHC stability, one input is missing => How much e- on average is inside the proton bunch? We have the central density but it is not enough => How much e- are inside the beam on average over the machine? (Action 2 for the e-cloud team).
5) Transverse impedance localization update (NB): pdf
- NB reviewed briefly the method and then discussed the measurements in the PS, SPS and LHC (not yet and will be done at the next ICE meeting).
- Meas. done in the past in CERN SPS and RHIC and also lepton machines.
- Observable = phase advance => The uncertainty chain
- Accuracy of phase advance detection for noisy sugnals.
- Accuracy of slopes for measurements with error bars.
- Impedance induced phase advance beating.
- Numerical studies by NB of the accuracy, extension of Sacherer's formula to include the beating (=> deltas is the Dirac function as there is a kink there).
- Measurements in the PS:
- QSE quadrupole current variation in the PS to check the model => NB could localize the 2 QSE (both slope and reconstruction were good), which is perfect, proving that the reconstruction method can work.
- Meas. with a single bunch in the V-plane:
- 2 GeV, nTOF bunch.
- Intensity scan from 1E12 p/b to 6E12 p/b.
- TFB used as vertical kicker.
- Smallest bunch length acheived = 90 ns (4 sigmas).
=> Measurements rather clean but difficult to conclude. What about contribution from RW and SC?
- Trying with tunes closer to half resonance Qy ~ 0.5, to increase the signal => But the optics model is very complicated close to the resonance due to the natural optics errors.
- Where are we vs. theory => NB replied that we have ~ 1/3 of the impedance compared to theory (only kickers included for the moment).
- Comments/suggestions:
- Is it interesting to constrain the model by imposing the relation between the different (computed) impedances that we (think we) know?
- Can we take the amplitude of each line, compute the impedance and compare with predictions (putting the results in a table below the plots)?
- Measurements in the SPS:
- Long time spent to improve the BPM situation (MOPOS system).
- Intensity scan from 4E10 p/b to 1.6E11 p/b with a LHCINDIV type beam on FB at 26 GeV. Chromaticity ~ 0 in V-plane.
- ~ 1000 turns analysed.
- Typical decreasing behavior and some hints on impedance locations (MKP, MKQ and MKE kickers).
- Plan to do test also with the TCSM collimator.
- Measurements in the LHC => To be discussed during the next ICE meeting.
6) Actions to be taken for the next meeting
- Old actions.
- New actions:
- Action 1 (e-cloud team): Explore the difference in photoelectrons between the ECLOUD and PyECLOUD codes in dipole fields.
- Action 2 (e-cloud team): One useful output of the ECLOUD-PyECLOUD codes could be the number of e- on average over the machine which is inside the proton bunch. We have the central density but it is not enough for some estimations.
7) Miscellaneous
- Deadlines and important dates for ICE.
- The next (76th) meeting will take place on 27/02/2013 => Agenda:
1) Impedance localization update for PS, SPS and LHC: Part 2/2 (NB),
2) Review of the 2012 activities and current plan for the 2013 ones for SC (FS).
- See preliminary agendas for the next meetings.
- See List of Actions.
Minutes by E. Metral, 26/02/2013.