Minutes of the ICE section
41th meeting on Wednesday 12/10/2011 (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), 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), Tatiana Pieloni (TP), Werner Herr (WH), Xavier Buffat (XB).
Present/Excused: BS, CH, CZ, HD, EB, EM, EW, FS, GI, GR, JLN, KL, NB, NM, OB, TP, WH, XB, Alexey Burov, Chandrashekhara Bhat, Georges Trad, Miriam Fitterer, Rama Calaga, Simon white.
1) Newcomers / visitors
- None.
2) Comments on the minutes of the previous 40th meeting + Actions
- None.
3) General infos
- No particular comment.
- SL meeting:
- Matlab: OliverB mentioned this issue at last BEMB => We will now ask IT for a cost estimate (thanks for the input you sent me!).
- Sasha (AM from KEK) => Long-term visit delayed for the moment and still ongoing discussions for a shorter visit.
- LHCb reached its goal of 1 fb^-1 on 03/10/11!
- Django Manglunki will be the new SPS light ion project leader as Stephane Maury became the ELENA's project leader.
- New group leader for the BE/ASR (Administration, Safety and Resources Group) group as Jean-Pol Matheys will go to HR. Ronny Billen will become the new ASR group leader.
- CERN pension scheme for new recruits (as of 01/01/2012). Reminder: Fellows are considered as staff members as concerns the pension as they contribute to it.
- SD1 TS (Technical Stop) => Certainly (at least) 2 years without beam => Earlier November 2014. As concerns the injectors, the restart is foreseen for June 2014.
- Follow-up of the transverse emittance blow-up from PSB till collisions in the LHC => VerenaK followed this up and it seems to come (at least partly) from the long LHC injection plateau and that a potential candidate could be IBS. GianluigiA will make a summary of the observations at this afternoon's LMC.
- BE retreat summary: A total of 7 posts for ABP in 2012.
- News on the LHC:
- LHCb reached its goal of 1 fb^-1.
- ATLAS and CMS with more than 4.5 fb^-1 (the 5 are within reach in the next few days).
- LHC is now alone as the Tevatron stopped on October 30th.
- LHC MD with 25 ns last Friday => High chroma (~17 Qprime) helped as predicted in the past by EB and FrankZ (very good!) and we succeeded to store many bunches (732b at 25ns circulating in B2 for some time with 5h lifetime), which is a very good start. Next MD on Friday to do the scrubbing run.
- Email from Gerhard Schneider for the LHC BGI: ... We see a pressure rise with beam in the BGI => assumption is, that we see some electron cloud, responsible the first rise, then we some synchrotron radiation responsible for the 2nd small rise of pressure. The third raise could be explained by a temperature rise in the BGI. Has the impedance of the BGI been calculated and would you suppose that a temperature rise due to the beam seems reasonable?... => Being followed up by the impedance team (Action 1). See some work done in the past: RLC meeting (17/03/06).
- Discussion with Vincent Baglin from vacuum about possible ecloud build-up in some LHC chambers with very large diameter (800 mm) => Being followed up by ecloud team for simulations's predictions (Action 2).
- Beam-beam team (XavierB) to study the evolution of the transverse emittances during stable beam during the high-pile up MD and deduce the Yokoya factor (as proposed by WernerH): Picture of high pile-up parameter space and Picture of Pi mode.
- Ecloud meeting: For the heat load, both for 25 and 50 ns it seems that we have more heat load for flat than for Gaussian bunches. Not yet understood why. Humberto will check his simulations and in particular the energy distribution for the next time.
- HDWG: KevinL scanned the octupole current needed at injection to stabilize the elcoud-induced fast vertical instability (assuming 4E11 m^-3, whereas the threshold is ~ 2E11 m^-3) => Need more than 100 A in the octupoles at LHC injection, which should not be possible in practice. What could be the maximum value? To be followed up.
- PS LIU meeting on TU=> Reminder: (At least) 10 kCHF/year are reserved if we want to invite someone etc. and this for the 6 years of the project until 2018.
- TCTP collimator impedance follow-up => Meeting with Fritz
and the impedance team on Monday and tomorrow => 2 directions:
Identify how dangerous these trapped modes would be. Try and damp them if
needed. No success for the moment.
- Suggestion from RalphA: Really look in detail at the ferrites installed in the LHC as it seems that all the structures were some heating is observed in the LHC are equipped with ferrite.
- Meeting on Friday (with PSB and PS experts and RolandG) about 3 questions EM raised in the past to try and increase the beam-brigthness: the 3-batch scheme, longer bunches from the PSB and longer bunches at PS injection => The 3 propositions were studied in full detail by all the experts and it was concluded that they cannot bring a significant improvement (if any) in beam performance => Some minutes from SimoneG should be available soon.
- Charged moving particle => Nice paper from GI, sent to him by RiccardoDM on the Lorentz-Dirac equation: http://arxiv.org/pdf/gr-qc/9912045v1.
- Final transverse emittance due to the ecloud-induced fast instability => Already in the list of actions of the HDWG.
- BEMB (03/10/11): Following the presentation at the LMC on the strategy of collimators production during LS1, P. Collier confirmed the decision that the EN Department will now buy the materials for 26 collimators (23 TCTPs and 2 TCSPs). A call for tenders will be sent out early next year for 18 of these collimators.
- Last LSWG => In particular discussion about future TDI MDs to try and improve our knowledge of both longitudinal and transverse impedances.
- Follow-up of beam-beam studies by Ji Qiang: Beam-Beam tune footprint.
- Computation of the impedance for the PS dummy septum (for MTE) => Being followed up by the impedance team (Action 3).
4) Highlights from IPAC11 (IPAC participants)
- WH => Nothing more that CERN's studies.
- NM on space charge, wake field and LHC transverse beam distribution (which is important for us for the stability diagram).
- GR:
- Ecloud related topics with in particular the collaboration with GSI to compute the beam energy loss due to ecloud (linked to the synchronous phase shift).
- Ecloud at LFNL (from PAC11) => Different behaviours with a-C compared to CERN's experience!
- Satellite meeting with German partners for project financing (CERN representatives: G. Arduini, S. Gilardoni, G. Rumolo, F. Zimmermann) => Possible subjects on which we can write a common project:
- 3D ecloud, long-term simulations with ecloud, materials & impedances, space charge.
5) Summary of Fermilab's MDs (FS): ppt
- Very interesting results on:
- Beam-beam resonances vs. beam separation.
=> Some observations could be consistent with some predictions that the situation is the most critical at ~ 1.5 sigma (in the plane of separation).
- Coherent beam-beam modes.
=> In the presence of beam-beam, many possibilities to choose the chromaticities, which is not the case in the presence of only 1 beam. In the latter case, linear coupling can also clearly help.
- AC dipole with colliding beams.
- Reminder: the goal was to excite the weak beam through the strong beam using the AC-dipole However, without excitation of the strong beam.
=> The measurement is tricky and once one eats into the beam distribution it is over.
- Betatron phase averaging.
- Reminder: the goal was to collide bunches at different beta* / bunch length ratios, as the theory predicts that the magnitude of beam-beam effects is strongly affected by this ratio.
=> Produced excellent data, in qualitative agreement with expectations!
- Side-show:
- Lots of expertise concerning space charge => Collaborations discussed.
6) Actions to be taken for the next meeting
- Old actions.
- New actions:
- Action 1: Impedance team to check the impedance and the induced heating of the LHC BGI as some heating might have been observed.
- Action 2: Ecloud team to study the ecloud build-up in some LHC chambers with very large diameter (800 mm), after some observations made by the vacuum people.
- Action 3: Impedance team to compute the impedance for the PS dummy septum (for MTE) => Will/could be studied by Mauro Migliorati when he comes to CERN as PJA.
7) Miscellaneous
- The next (42th) meeting will take place on 19/10/2011 => Agenda:
1) Can circular optics be useful for upgrades of the LHC complex (Alexey Burov).
- See preliminary agendas for the next meetings.
Minutes by E. Metral, 12/10/2011.
