Minutes of the ICE section
37th meeting on Wednesday 24/08/2011 (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, Giulia Papotti, Georges Trad, Hannes Bartosik, Octavio Dominguez, Rama Calaga, Raymond Wasef.
1) Newcomers / visitors
- None.
2) Comments on the minutes of the previous 36th meeting + Actions
- None (as not yet available...).
3) General infos
- SL meeting:
- Safety structure : The DG sent a memo to inform of a new safety structure for the whole accelerators complex (not based on the department). Steve Myers has been appointed as the Complex Manager.
- HIE-Isolde : the technical coordinator has been replaced by the project leader (Y. Kadi).
- Next BE retreat on September the 30th : ELENA posts to be discussed.
- CMAC:
- New problem reported by TE about diode connections. The situation is still preliminary, but it could be a serious issue.
- MDs should be preceded by a study to simulate possible results.
- oPAC fellows: eight are for CERN, and three Marie Curie fellowships have been agreed for ABP (three for BI). Job descriptions have been prepared by Oliver: H- injection, HL-LHC, LHeC.
- Mini-Chamonix => Action 1 for impedance team: evaluate impedance vs. bunch length (to try and understand LHC's observations of heating/outgassing). The bunch spectrum was measured and it will be used to review the estimates.
- LMC: new vacuum pipe for CMS was approved. It was mentioned that the central tracker cannot be installed during LS1 and it will be too late in LS2. Hence, CMS is going to request a five-month winter technical stop between LS1 and LS2. This request is not approved, yet.
- BEMB: special meeting on 20/9 for fellows.
- News on the LHC:
- Special LMC on Wednesday 17/08/11 to discuss the study of beta* = 1 m and 3rd LHC MD block.
- TDI => Some heating is observed on both TDIs (2 and 8) and the impedance (trapped modes) is suspected. SteveM would like to have a calculation of the impedance vs. gap => To be followed up by the impedance team. We could also plan some bench measurements on spares. See the link http://lhc-impedance.web.cern.ch/lhc-impedance/LHC_equipments.htm#TDI where we collected all the (historical) info about TDI. I contacted Oliver Aberle to have more info. BrennanG is organising some meetings to follow this up.
- SLAC phase 2 collimators => I sent an answer to TomM to tell him that they have to damp their transverse trapped modes which are ~ 1000 times higher than in the current CERN collimators.
- News from Ji Qiang on the PS Montague resonance simulated using the 3D IMPACT code => Dynamic crossing starting from Qx = 6.245 instead of 6.15 (i.e. from above the diagonal instead of from below): Picture1. To be compared to the other case presented at ICE 03/08/11.
- StefanoR informed me that on Sunday 21/08/11 they did the test (end-of-fill) with the tight collimators' settings and everything went fine., i.e. no instability and even no tune shifts measured => Summary in the ELogBook (Sunday 21/08/11 at 16:07) from SR and DW:
- We worked on B1 and moved in the TCPs of IP7 to tight settings (4 sigmas). We observed loss spikes while getting close to the beam in steps of 5 microns. The BLM spikes were under good control and far from dump limits. This suggests that the population of the tails between 5.7 sigmas (initial settings) and 4 sigmas (tight settings) are moderate even after 8 hours of physics. While moving the TCPs, we observed reductions of lifetime for b1, down to a minimum of ~25h. Once the TCPs were in place, the lifetime was going back to previous values. We managed to move in all the TCGSs of IP7 to 6 sigmas.
- We observed no apparent impact of main beam parameters (lifetime, tune, losses) - to be confirmed by detailed analysis. We stayed in these conditions during about 5 minutes, which can be considered a proof of principle of tight settings in IP7. While moving in the TCSG in IP6, beams were dumped by the SIS interlock that checks the retraction between TCSG and TCDQ.
- Email I sent on new job positions: https://ert.cern.ch/browse_www/wd_portal.search_results?p_web_site_id=1&p_category_id=1&p_show_results=Y&p_form_type=CHECKBOX&p1=2&p1_val=Staff&p2=4&p2_val=Physicists&p_text=&p_save_search=N.
- Observation of instability (cured by octupoles?) during studies with beta*=1 m during the night between Saturday 28/08/11 and Sunday 29/08/11 => See talk given by EM at the LBOC (30/08/11) + talk given by Jorg where it seen that the BBLR plays a crucial role in these observations.
- NM computed the tune shifts with tight collimators' settings => See talk given by EM at the LBOC (30/08/11).
- Action 2 for the ecloud team from LBOC meeting (30/08/11): Stabilization of the fast ecloud instability at LHC injection with octupoles (instead of chroma): Which octupole's current would be needed?
4) Preliminary analysis of the ADT data from LHC ecloud MD 26th August (Hannes Bartosik): pptx
- Analysis of 2nd dump of LHC 25ns injection MD:
- (after 12 bunches) B2 injection of 48 bunches with 25ns spacing with transverse dampers off,
- Protection dump due to losses after around 500 turns (previous injection with transverse dampers was dumped after around 1000 turns),
- Injection itself looked clean,
- Around 30s before injection: perturbation on 3.3kV line => Cryo plant in point 2 lost around 30s after injection.
- No particular observation on BBQ data (probably due to fast time scale).
- Analysis of 73 turns before the dump from the ADT (damper) pickups (Q9) of all bunches is presented .
- Increased coupled-bunch motion after ~ 20 bunches.
- Several analyses done: SVD (spatial and time reconstruction), mountain range of bunch motion, single-bunch FFTs (over 73 turns), tunes along the batch (with NAFF) => ~ + 5E-3 in QV (with a possible ecloud saturation after ~ 28 bunches?), estimations of the rise-times => ~ 10-20 ms?
- It seems therefore that there is a low-frequency coupled-bunch instability, which the ADT should be able to damp! To be followed-up.
5) Headtail simulation studies of Landau damping through octupoles in the LHC (Raymond Wasef): pdf
- Successful check (with HEADTAIL) of the (theoretical) shape of the stability diagram (for a Gaussian transverse distribution) for a single LHC bunch at 3.5 TeV with an octupole current of - 10 A.
- Next steps:
- Check the reason why there is a factor 2 between HEADTAIL and the theory (HEADTAIL needs ~ 2 times less octupole current):
- Error in stability diagram implementation,
- Error in the HEADTAIL conversion of the octupole current,
- There is a difference between theory and simulation.
- Finalize the work with the + 10A curve.
- Study several transverse distributions and in particular the quasi-parabolic one used for the LHC estimates made in the past.
6) Electron Cloud Observation in the LHC (GR): pdf
- Several electron cloud effects seen in the LHC in 2010 2011:
- Pressure rise around the machine, especially pronounced in the common vacuum chambers,
- Heat load in the arcs measured with 50 ns and 25 ns beams,
- Electron Cloud Instability observed with 50 ns beams and incoherent effects for 75 ns beam,
- Bunch spacing dependent synchronous phase shift to compensate for energy loss due to the beam-cloud interaction.
- Visible mitigation of electron cloud could be achieved thanks to machine scrubbing => Smooth operation with 50 ns beams now possible.
- 25 ns beams for future operation?
7) Observations of Beam-Beam Effects at High Intensities in the LHC (WH): pdf
- First clear beam-beam observations in the LHC are presented.
- Obtained large head-on tune shifts above nominal.
- Effect of long range interactions clearly visible.
- Number of head-on and/or long range interactions important for losses.
- All observations in excellent agreement with expectations and well understood.
- Beam-beam effects should allow nominal luminosity (at 7 TeV).
8) THE EUROnu PROJECT: A High Intensity Neutrino Oscillation Facility In Europe (EW): pdf
- FP7 Design Study.
- Focus on possible next generation neutrino oscillation facilities in Europe:
- CERN to Frejus Superbeam (SB),
- Neutrino Factory (NF), in collaboration with IDS-NF,
- Beta Beams (BB),
- Performance of baseline detectors and physics reach.
- Aim: comparison of physics, cost & risk.
- Reported to CERN Council via SG/ECFA.
- Project started: 1st September 2008.
- Duration: 4 years completion in August 2012.
- Superbeam favored by T2K hints.
- The Superbeam is a well proven technological option for the next round of experiment towards CP violation!
- CERN Specific, Beta Beam favored by T2K hints:
- End-to-End simulations and optimisations needed,
- Handling space charge & collective effects in PS and SPS.
- Planned experiments at CERN ISOLDE.
9) Actions to be taken for the next meeting
- Old actions.
- New actions:
- Action 1: Impedance team to evaluate impedance vs. bunch length (to try and understand LHC's observations of heating/outgassing). The bunch spectrum was measured and it will be used to review the estimates.
- Action 2: Ecloud team to study the stabilization of the fast ecloud instability at LHC injection with octupoles (instead of chroma). Question raised during LBOC meeting (30/08/11).
10) Miscellaneous
- The next (38th) meeting will take place on 14/09/2011 => Agenda:
1) Past predictions for Longitudinal Loss of Landau damping and Longitudinal Mode Coupling and comparison with the recent results from Alexey Burov (EM)
2) May resistive-wall drive longitudinal coupled-bunch instability? (Alexey Burov)
- See preliminary agendas for the next meetings.
Minutes by E. Metral, 09/09/2011.
