Minutes of the ICE section
33th meeting on Wednesday 27/07/2011 (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, Eirini Koukovini Platia, Fritz Caspers, Georges Trad, Hannes Bartosik, Raymond Wasef.
1) Newcomers / visitors
- None.
2) Comments on the minutes of the previous 32nd meeting + Actions
- The last 2 minutes are already available with the general infos but the summaries of the talks are still missing.
3) General infos
- Comment from AlexeyB => Discussions with NM, HeikoD and JoachimT on the longitudinal coupled-bunch instabilities:
- How do they look like when the bunches are not equally spaced / the machine is not filled?
- Do they always exist?
=> AlexeyB could discuss this subject at some point. Next week Alexey will talk about the (single-bunch) loss of longitudinal Landau damping.
- SL meetings of the last 3 weeks:
- M. Jimenez will take over the role of deputy Consolidation project leader and has been appointed as TE/MME group leader.
- SAPOCO (SAfety POlicy COmmittee): S. Maury will be replaced by V. Mertens.
- ELENA was approved by the Research Board. S. Maury will be project leader for 2.5 years with C. Carli as deputy project leader, who should then take the role of project leader.
- PAX Experiment (in AD) was not approved.
- The neutrino at PS physics case is taking momentum.
- The BE Workshop will be organised also this year.
- American and Australian colleagues have reported difficulties in opening a bank account in UBS. In principle, the CERN salary can be transferred to any Swiss (and maybe even in French) banks.
- R. Veness is going to join BI Group.
- No more cryo-collimators development following the collimation review. Installation of DS collimators will not take place on LS1.
- RCS could be ready by LS2!
- News on the LHC:
- Mini-Chamonix workshop took place on 15/07/11: http://indico.cern.ch/conferenceOtherViews.py?view=standard&confId=144632 => Talks in particular of GR on Instabilities and transverse feedback etc., of WH on beam-beam limits and of JanU on beam induced heating and bunch length dependence.
- If I understood well, at the mini-Chamonix workshop there were some discussions about the observation (or not) of a transverse coupled-bunch instability with a head-tail mode higher than 0. I think that we saw it for instance during the LHC scrubbing run in 2011 => Following link: http://emetral.web.cern.ch/emetral/ICEsection/2011%20LHC%20Scrubbing%20Run.htm (paragraph on (Clear) coupled-bunch motion in H observed on Wednesday 13/04/11...).
- The LHC is now using the double-batch 50 ns beam from the PSB (instead of the single-batch) to have smaller transverse emittances. These days the maximum number of bunches (1380) is used with ~ 1.2E11 p/b (above this value many problems are observed with vacuum etc.) and transverse emittances of ~ 2.4 microm in collisions, giving peak lumies of ~ 1.6-1.7E33 (1.8E33 was seen with ~ 1.3E11 p/b but the beam did not reach stable beam conditions).
- Some vacuum problems mentioned the last days might be explained by the wrong polarity used for LHCb leading to larger LR effects than normal => The polarity was corrected.
- Beam-beam MDs on both HO and LR => For the LR studies the nominal machine was used, with trains of 36 bunches (50 ns spacing) and then the crossing angle was reduced to enhance the LR effects. Data still being analyzed but all the observations seem close to the predictions: loss of DA as predicted, PACMAN effects as predicted (orbit, tune and DA) => ~ 1 sigma lost between all the LR interactions and 1/2 the LR interactions.
- Observation by Sandra et al. at PS transition of an instability at a much smaller intensity as usual: Picture 1. The threshold intensity seems to be ~ 280E10 p/b for a longitudinal emittance of ~ 2.2eVs, whereas in the past we could send more than 8E12 p/b with this longitudinal emittance => To be followed up.
- Email from Federico Carra => TCTP tapering => To be followed up by impedance team.
- OMCM workshop => Talk by Michael Plum on the well understood extraction kicker instability: the measured and simulated instability rise-times are both equal to 1036 turns!
- Kick-off meeting for LIU-SPS ecloud study organised by Miguel Jimenez on 20/06/2011:
- Action for us there: which part of the SPS machine needs to be coated? Put the info on some slides, present it at some meeting and then we could refer to it in the future.
- Discussions about impedance issues and communication (to be followed up by the impedance team):
1) Thickness of copper coating needed => Should be consistent with what was recommended in the past by L. Vos: ~ 0.8 mm copper coating for diameter of 80 mm => Then scaling with the radius (1 / b^3) for the coated thickness requested. Did we say something else at some point?
2) Effect of the NEG coating => It was measured and mentioned by Fritz that NEG coating (of few microns I imagine, tbc) is OK. Do we have now different results? In which conditions? etc.
- Follow-up of the different possible heatings observed in the LHC (before my vacation):
- Collimator => Is it real? At the LHC 08:30 meeting of 21/06/11 it was reported that the collimator cooling capacity was increased => Let's see the effect on the temperature increase. Is it real or a measurement error?
- MKI => It seems to increase steadily and therefore seems real. Can we reproduce it?
- Beam screen => It seems there is a threshold effect from cryo measurements from Serge? What is the real impedance?
- We are in contact with RF (PhilippeB) to have the bunch spectrum. RalphS already sent us a spectrum taking the FFT of a measured longitudinal profile.
- Some BSRT measurements by FedericoR for the fills 1883 and 1875: Slides.
- Circular modes, beam adapters, and their applications in beam optics (by A. Burov, S. Nagaitsev and Y. Derbenev): http://pre.aps.org/abstract/PRE/v66/i1/e016503.
- Effect of bunch length on the cryo system (from Serge Claudet and Laurent Tavian): 2 slides.
- Arcs: about 2K increase due to injection of 2x1092 bunches, followed by avg 1.6K due to ramp, but from 0.6K if bunch length > 1.2 ns to 2.5K if BL < 1.13 ns (see file).
- Stand-alones: most likely dominated so far by static losses that we have to better understand, Q6 mostly affected by the beams.
- Triplets: Very sensitive to injection, rather moderate effect of ramp, L8 & R2 receiving the maxi power.
- Moreover, the recent efforts to better control the beam screen temperature helped them to identify few loops in some arcs that have largest beam induced heat loads than the rest. They continue with this and should come with less than 5% of the cases were NC could be identified, and hopefully fixed during next long shut-down.
- For this summer and now that they better master the effect at injection, they have in mind to restore some calibrated cells (standard and abnormal) for more accurate measurements in mW/m.
- Joint HL-LHC and LIU Brainstorming Session on Friday 24/06/11 morning: https://indico.cern.ch/conferenceDisplay.py?confId=138437 => EM gave in particular the following talk: Single-bunch intensity limit in the LHC (transverse). The summary can be found at: https://edms.cern.ch/document/1154537/0.1.
- IMPORTANT (reminder): Concerning IPAC2011, please note that the deadline is 31/08 (for IPAC). But we need first to send the papers to OliverB for the 22/08 (the papers will then be sent to PaulC for 26/08).
- Email from Ralph Assmann about written report for collimation review:
- Committee report now linked at http://indico.cern.ch/event/collreview2011.
- The feedback from the report reflects on the excellent work performed by all of you. My compliments and thanks to you and your colleagues for the performance that we can deliver. Our collimation system (on which we spent so much time and effort over the last 9 years) is a full success and we can be proud of this achievement! We will organize a drink after the summer break to strengthen ourselves for the work ahead. Please feel free to distribute this info to anybody concerned. My selection of key statements from the report:
- "The general progress of LHC, and particularly the performance of the collimation system, is outstanding."
- "It is worth noting that the collimation system performs two critical roles: in its cleaning role it prevents protons from impacting the LHCs cold mass; its secondary role is as passive protection in certain beam loss scenarios. In both roles it has performed impeccably."
- "The committee is impressed by the quality of the design and preparatory engineering work on the special collimator units foreseen for installation in the cold magnet string of IR3."
- "collimation performance and limitations are properly analyzed and adequately addressed by the upgrade plans"
- "On the basis of the evidence presented, the committee concludes that the nominal proton beam intensity of LHC at 7 TeV can be achieved without the installation of additional collimators in the IR3 dispersion suppression region during the LS1 shutdown."
- "For heavy ion beams less experimental evidence exists and thus the extrapolation to full energy entails more uncertainty."
- "the committee feels that the proposed installation of BPMs embedded collimators should take high priority"
- "The committee feels nevertheless that the upgrade of collimation in the IR3 and IR7 DS should be carried out in the long term (LS2) as it will allow for increased machine performance."
- "If the proposed mitigation measures go ahead as planned, they should be sufficient to reduce R2E effects at IR7 to an acceptable area. In this case, the shift of betatron cleaning to IR3 will not be required. It is felt, however, that preparation for the move should be undertaken."
- A possible surface treatment for increasing the Q-value of Nb cavities at least at low field (from prof. V. Palmieri, Legnaro): http://www.youtube.com/watch?v=Hqv7lkVeasI.
- An instability has been observed with a pilot bunch in the LHC with a negative chroma (email from Riccardo. Thanks!) => In the logbook at 2:15 on 3/7/2011 (https://ab-dep-op-elogbook.web.cern.ch/ab-dep-op-elogbook/elogbook/eLogbook.php?shiftId=1036348). According to our predictions (NM), the instability rise-time should be for these parameters (1 bunch of ~ 1.25E10 p/b, Q' ~ -14, at the start of the ramp): ~ 1-2 s, which should not be too far from what we could roughly deduced from the picture (to be done properly).
4) Main activities and news from the HEADTAIL WG (GR): pptx
- GR reviewed the general simulation principles of the HEADTAIL_ecloud and HEADTAIL_impedance codes and explained the reason of this working group.
- HEADTAIL has been already used (successfully) in many machines (PSB and LHC are missing in the list...).
- GR reviewed the mandate, goals and organization etc.
- There are now only 2 versions of the HEADTAIL code, HEADTAIL_impedance and HEADTAIL_ecloud, which can be found under svn:
- CERN Central SVN Service page.
- The svn repository can be accessed via WEBSVN for CERN users or WEBSVN outside CERN.
- HEADTAIL repository: hdtldev => Here the code can be downloaded. Any HDWG member can then modify it and upload it. The code will be then assigned a new version number and all changes are tracked.
- HEADTAIL_ecloud repository: hdtl-ecld => Same thing as above.
- Several meetings already took place, with many interesting subjects to follow.
- Comment by FritzC: As it seems we observe some unexpected heating in the LHC, Fritz proposed another subject to study in detail by careful numerical simulations => Coherent magnetron effects which could lead to heating of the cold bore (behind the beam screen). For the magnetron effects to take place, we need electrons, a beam and trapped modes. Some electrons could then go through the beam screen holes and heat the cold bore. Fritz mentioned also the transition from incoherent to coherent emission.
5) PSB beam brightness increase by a factor 2 (EM): pdf
- EM presented a possible new scheme using a 3-batch injection between the PSB and PS machines (3 times 4 = 12 bunches in the PS on h14) instead of the nominal 2-batch scheme (6 bunches in the PS on h7).
- Some issues are discussed.
- Next step: AlanF in the PSB will do some tests in the next few weeks to try and see which bunch length can be achieved at extraction.
- Discussing with ChristianC, it seems this scheme could also be useful with LINAC4 in some cases.
6) Update of the impedance of new LHC experimental beam pipes (BS): ppt
- The vacuum group is looking at the opportunity to replace
the current LHC experimental beam pipes by composites:
titanium (or Aluminum) + carbon-carbon. NEG coating of 3 micron would still be
put on the inside.
- Recommendation: Use a thickness for the Aluminum coating of (at least) 5 microns.
- Discussion to check the properties of the NEG with the experimental setup of CZ for the ferrite characterization.
7) Actions to be taken for the next meeting
- Old actions.
- New actions => Followed up in the different working groups.
8) Miscellaneous
- The next (34th) meeting will take place on 03/08/2011 => Agenda:
1) Impedances of the new PS wire scanner (JLN and OB)
2) Loss of Landau damping for longitudinal bunch motion (Alexey Burov)
- See preliminary agendas for the next meetings.
Minutes by E. Metral, 27/07/2011.
