Minutes of the ICE section
29th meeting on Wednesday 25/05/2011 (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), Xavier Buffat (XB).
Present/Excused: BS, CH, CZ, HD, EB, EHM, EM, EW, FS, GR, JLN, KL, MCAP, NB, NM, OB, TP, WH, XB, Georges Trad, Javier Cardona, Raymond Wasef.
1) Newcomers / visitors
- None.
2) Comments on the minutes of the previous 28th meeting + Actions
- Still need to write them.
3) General infos
- No particular comment from anyone.
- SL meeting:
- Staff Association: M. Ludwig mentioned that Uniqa has decided that from May 31st, no claims for medical reimbursement will be accepted after one year (in the past one had 2 years to get reimbursed).
- The works in building 6, 8, 9 and 10 may lead to more trouble than expected due to asbestos around some pipes. Some temporary work places might be necessary.
- LMC: Discussion about the Technical Stops (TS): it seems that there will not be any changes this year except in the case of a VIP visit (one is already foreseen beginning of July). For next year the TS could be extended by one day (total of 4 working days) and take place 5 times a year.
- News on the LHC:
- New peak lumi record on Monday with ~ 1.1E33 and the integrated lumi is ~ 350 pb^-1.
- Issue still to be understood => Transverse emittance blow-up on some batches after injection => See today's talk: Analysis of some LHC fills with TEBU at injection.
- SPS: The (small) transverse emittances of the 25 ns beam seem to be confirmed => ~ 2.5 - 2.9 microm for ~ 1.15E11 p/b.
- Collimation review on TU 14/06 and WE 15/06 => An update of the impedance model (and related instabilities) is needed for several collimators' settings. Action 1: NM.
- MD report at yesterday's LBOC: beam-beam and TCBI => Several comments from Lyn Evans to take into account for the next presentation on this subject: (1) beam-breakup type (where the tail of the batch does not talk to the head) or TCBI type (where the tail of the batch talks to the head)?; (2) For the measurements at injection, when Qprime was negative, didn't we observe only the head-tail instability (and not the TCBI)?; (3) What about the tune shift vs. intensity at top energy? (=> Still to be done).
4) 1st LHC beam-beam observations in 2011 (TP): pdf
- Outline:
- 1st collisions in fill 1603 with Schottkys,
- Leveling in IP8,
- Beam-beam HO MD.
- 1st collisions in fill 1603 with Schottkys:
- Reminder: The ADT is always on in collisions so BBQ measurements are difficult. Furthermore, the BBQ cannot select bunches to measure (pacman or super-pacman bunches). The beam-beam optimization is based on the pacman and superpacman knowledge => Thats why the Schottky measurement is an important tool for tune optimization during collisions.
- Reminder: The Schottky measurements are good in relative but not in absolute. How to relate tune shifts to Schottkys still needs some work.
- The positive horizontal tune shift and negative vertical one could be observed for the bunches colliding in ALICE (IP2) with an horizontal separation of 4 sigmas, as predicted.
- Negative tune shifts in both planes could be measured for the bunches colliding in IP1 without separation, as predicted.
- Leveling in IP8:
- Reminder: LHCb (IP8) wants to operate at reduced luminosity and a separation of 0.5-2σ, which can give a reduction factor 3 in lumi, but the question was: Can we operate the LHC with a separation in IP8? => The tune diagram space occupied by the detuning with amplitude of particles is reduced thats why it should not be a worry, which was confirmed in measurements.
- Important:
- The fact that it is OK in this configuration doesnt mean that it will always be OK.
- LR will change the dynamics.
- Beam-beam HO MD:
- Reminder on the motivation => Experimentally probe the HO beam-beam effects by exploring the achievable beam parameter space to highlight future goals for the LHC and possibly HL-LHC (high intensity and low transverse emittance).
- MD conditions:
- Injection energy (450 GeV/c) & op/cs (β* = 11 m),
- Collision tunes Qh = 0.31 and Qv = 0.32,
- Nominal crossing angles and parallel separation,
- IP2 and IP8 spectrometers magnets off,
- ADT off during BB measurements.
- TP showed some predictions => Small and very slow emittance growths, which are currently re-studied by Ji Qiang with the real MD parameters.
- 5 fills were studied with bunch intensities between 1.6 and 1.95E11 p/b and transverse emittances between 1.2 and 1.6 microm => Several interesting measurements done, with as main results:
- Some emittance blow-up occurs during lumi scan optimization.
- Vertical BB tune shift brings the beam core on top of the 10th order => vertical plane affected.
- Horizontal tune shift well below the 10th order.
- BBQ raw data show instability developing in vertical, with a rise time of the order of 1 s.
=> Working point change to have Qh = Qv = 0.31:
- Collisions IP1 bring both beams tunes at Qh = Qv = 0.29, i.e. the beam core jumps the 10th order resonance.
- Observations: BB tune shift for 2 IPs = 0.034, with no lifetime drops and no losses.
5) Actions to be taken for the next meeting
- Old actions.
- New actions:
- Action 1 (NM): Prepare an update of the impedance model (and related instabilities) for several collimators' settings (to be sent by the collimation team), for the collimation review on TU 14/06 and WE 15/06.
6) Miscellaneous
- The next (30th) meeting will take place on 01/06/2011 => Agenda:
1) Main activities and news from the Impedance WG (BS)
- See preliminary agendas for the next meetings.
Minutes by E. Metral, 05/06/2011.