Minutes of the ICE section
93rd meeting on Wednesday 02/10/2013 (08:40-10:30, 6/2-004)
ICE members: Adrian Oeftiger (AO), Andrea Passarelli (AP), Benoit Salvant (BS), Carlo Zannini (CZ), Danilo Banfi (DB), Daria Astapovych (DA), Elias Metral (EM), Elena Wildner (EW), Frank Schmidt (FS), Giovanni Iadarola (GI), Giovanni Rumolo (GR), Javier Barranco (JB), 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: AO, AP, BS, CZ, DB, DA, EM, EW, FS, GI, GR, JB, KL, NB, NM, OB, SP, SRF, TP, WH, XB, Alexex Burov (FNAL), Andrea Passarelli, Simon White.
1) Newcomers / visitors
- DariaA will now be supervised by NM (as AlexeyB left CERN in July) and we continue to work on the LHC transverse stability for HL-LHC.
- Coombs George Rufus is a trainee (from EPFL, and in fact an ERASMUS student from Imperial college) with beam-beam team (TP et al.) to work on leveling etc. for after LS1. He will be here from October 2013 till July 2014, 3-3.5 days / week.
- PHD student with MassimoG (HIRLANDER Simon) to work on Laslett tune shift etc., started on 01/10/2013.
- Technical student with ElenaB to work on PSB (Magdalena Kowalska), started on 01/10/2013.
2) Comments on the minutes of the previous 92nd meeting + Actions
- No comment.
3) General infos
- No particular comment from anyone.
- SL meeting (I was not present):
- Changes in HR: Sudesha Datta will be the new ombudsperson.
- The students committees will take place from now on in January and June.
- A VIA cannot apply to a CERN fellow position.
- Several reports at the last LMC: BB workshop (TP) and Ecloud (GR).
- Recent LHC TCTP issue => Action for us (impedance team): any pb if gap of 0.5 - 1 mm with a beam screen cut in 2 or 3 pieces? (see Action 1 below).
- Some decisions taken for the Cu coating of the LHC TDI.
- LHC-CC13 workshop => http://indico.cern.ch/internalPage.py?pageId=2&confId=269322.
- Change in the contract extension procedure for the doctoral students (minutes of the Technical/Doctoral/Administrative Student Committee which took place on 23.04.2013) => The initial doctoral student contract will be for 6 months (instead of 1 year), followed by two extensions of one year each and then by the final extension of 6 months. The advantage of this scheme would be the following:
- The first 6 months are considered as a probation period. If the student is performing well his contract will be extend for 1 year by a simple PAF without progress report. In case of major issues this will enable a face-saving termination for both parties.
- 1.5 years are seen as a milestone where a progress report is required and the Professor should confirm that the doctoral student is on track for achieving a PhD. Ideally for these discussions the University Professor should be invited to CERN by the group concerned. If everything is going well, the contract is extended for one year.
- At 2.5 years: A progress report is required and the doctoral student should be on track to complete the thesis during the next six months. An extension of six months is normally granted upon production of a progress report signed by all parties.
- 3 years: Maximum doctoral student contract length (this is unchanged). The thesis should normally be complete by this time.
- Discussion between AlexejG and AlexeyB about additional Landau damping with an RF quadrupole => Ongoing (to be put in the NHTVS).
- SC meetings => Discussion in particular about all the LIU requests and work program => Add also the values for emittance BU and beam loss per machine (which are still the same as initially proposed, as they were checked last year in the injectors as GR mentioned).
- Seems that RaymondW obatined nice results with IMPACT code for the case of the SC studies at PS injection with the nTOF beam => To be discussed soon.
- WP2 meeting where BS presented the scaling beam-induced RF heating to HL-LHC parameters => See actions today (http://emetral.web.cern.ch/emetral/ICEsection/2013/2013-10-02/ActionsForRLIUPandWP2_EM_02-10-13.pdf).
- IBIC conf. and EM discussed there in particular with Monika Balk (=> Reminder: CST course next week). Several new and interesting features, as for instance the possibility to define a parent design and children projects (eigenmode, thermal, stress and sensitivity) and if we change a dimension of the parent design then it updates all the children simulations...Seems nice... Another interesting subject was on SOLEIL (1st light source with extensive use of NEG coating, ~ 50% of the circumference) => After 6 years of operation, damages occurred (this is understood and known at CERN, as discussed with Paulo Chiggiato: due to fluorescence induced by synchrotron radiation and the use of Cu is in this case much much better than Al, as used in SOLEIL).
- Workshop on Instabilities, Impedance and Collective Effects on 16-17 / 01 / 2014 at SOLEIL (GR involved).
4) Debriefing and follow-up of the LPL review (EM): pdf
- EM discussed
- Debriefing, comments from OliverB and some comments made during the workshop.
- Cogging MD:
- After some more analysis, it seems clear that the B2H signal disappeaed at the (very) beginning of the cogging process, i.e. while the 2 beams were still seeing each other and not when they did not see each other anymore.
- More data analysis being done by GI, in particular on the induced tune split, etc. => To be followed-up.
- Follow-up and next steps.
- We all agree that we should have an automatic logging to be made (a la Riccardo or something else) to be sure that there is neither duplication nor data loss => Somebody needed and this would be discussed inside the group.
- Comments from RalphS (by email) about the BBQ (reminded also by NM):
- The nominal BBQ system (as used for the Tune-FB) has been gated on the first six bunches on a regular basis since about October last year. Thus the regular system was blind for most of the instability effects (first six bunches very stable).
- However, we (eventually) added a second 'high-sensitivity' BBQ system that retained the non-gated 'instability monitoring' functionality and that was also logged in the MDB/LDB.
- The end-of-squeeze instabilities seemed to be -- for most of the observed cases -- related to intra-bunch motion, as indicated by
a) the large signals seen by the BBQ/MIM (close to saturation) while not being detected by regular BPM-type electronics measuring the rigid-bunch oscillation component (i.e. ADT, LHC-BPMs),
b) fundamentally different MIM spectra amplitudes in the 0.4, 0.8, 1.2 and 1.6 GHz bands that were beyond what one would expect due to simple chromatic effects (-> see IBIC'13 talk). While this is indicative of intra-bunch motion, due to the limited number of bands one cannot fully disentangle whether these were head-tail or TMCI-like effects. There are about 3 TB of MIM data confirming that the effect was fairly reproducible for every fill since Summer last year: /afs/cern.ch/project/ACAS/HeadTail .
5) Reflections on LHC Transverse Instabilities (Alexey Burov): pdf
- 3-beam instability model developed, but which does not pretend to be fully exact => Need to check all the assumptions and what the precision is (order of magnitude? More? Less?).
- Ecloud => Both wake (in fact it is a generalised wake which depends on both z and z' and not only z -z' as for a classical wake, but here the classical wake is assumed) and nonlinearity (which was not included in the work of Peredeventsev for instance).
- Some discussion about the model of AlexeyB and the several assumptions.
- GI proposed to check the model of impedance and ecloud with HEADTAIL => Still to be done. AlexeyB could compare his approach to the ecloud instability at injection as there ecloud dominates over impedance and we can remove BB effect => Would be very interesting to see the result.
- Stability diagram with ecloud => To be thought about how we can extract it from HEADTAIL and what it really means.
- AlexeyB compared the case for LOF > 0 and for LOF < 0. Reminder: in the plots, q is in unit of Qs.
=> LOF < 0 is much better as no instability is predicted (with this model. There is still the possible issue of BB and octupoles fighting against each other at few sigmas but cannot be treated here and possible strong HT instability if the ecloud would be an order of magnitude higher).
- GI and GR commented that they expect a very small effect of transverse beam emittances on ecloud build-up.
- Reminder on the non-monotonic behaviour of ecloud instability.
- AlexeyB explained
- Why at the EOS,
- What happen at injection compared to 4 TeV,
- The possibility to explain the observed humps mentioned by KL,
- The poor reproducibility,
- Why he does not believe in damper imperfections.
- AlexeyB suggested his MD priority list.
- Finally, AlexeyB suggested to communicate in the future via a web-based "ICE forum" for those interested to sign, which he proposed to start soon.
- SUMMARY AND CONCLUSION:
- The current model developed by AlexeyB (3-beam instability) is a first attempt to describe analytically a very intricate problem, which is therefore very nice and it contains for sure several very interesting features.
- BUT, there are several important assumptions which need first careful analysis and check and it can therefore reasonably not be used at the moment to make predictions or try and explain observations at the required level of precision.
6) Actions for the RLIUP workshop and HL-LHC WP2 (EM): pdf
- Could not be discussed during the meeting due to time constraint => Please have a look to all the actions... (see Action 2 below).
7) Actions to be taken for the next meeting
- Old actions.
- New actions:
- Action 1 (Impedance team): Some problems found recently with the TCTP (more precisely with the vacuum firing of the steel plates that go along the collimator jaws, and also serve as screen of the ferrites, to absorb the emitted heat). The problem is probably related to the sandblasting procedure used to improve the emissivity. One possible solution to reduce deformations during the vacuum firing might be to cut them in 2/3 pieces and then assembled. This procedure risks however to leave some small transverse gaps, probably below 500micron. Do we see any potential issues if there are these gaps?
- Action 2 (All the team): Actions for the RLIUP workshop and HL-LHC WP2.
8) Miscellaneous
- Deadlines and important dates for ICE.
- The next (94th) meeting will take place on 23/10/2013 => Agenda:
1) Brief reports of the 4 WGs (by the WG leader or replacement) => Plan, activities, deadlines, issues, etc.: BB, SC, EC, IMP.
- See preliminary agendas for the next meetings.
- See List of Actions.
Minutes by E. Metral, 02/10/2013.