Minutes of the ICE section
76th meeting on Wednesday 27/02/2013 (08:40-10:30, 6/2-004)
ICE members: Benoit Salvant (BS), Carlo Zannini (CZ), Danilo Banfi (DB), Daria Astapovych (DA), Hugo Alistair Day (HD), 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), Serena Persichelli (SP), Sergio Rioja Fuentelsaz (SRF), Tatiana Pieloni (TP), Werner Herr (WH), Xavier Buffat (XB).
Present/Excused: BS, CZ, DB, DA, HD, EM, EW, FS, GI, GR, JLN, KL, NB, NM, OB, SP, SRF, TP, WH, XB, RaymondW, JosephK, AlexeyB, MichelM, AlexanderH, MichaelB, VincenzoF, TatianaJ, LetiziaV, MauroM, ElenaB, FritzC, SimoneG.
1) Newcomers / visitors
- Joseph Kuczerowski (from PS-OP) who will help us with bench impedance measurements (started few days ago and until ~ May 2014) => In the new Impedance Lab in room 8-R-006. Welcome Joseph anf many thanks in advance!
2) Comments on the minutes of the previous 75th meeting + Actions
- No comment.
3) General infos
- No particular comment.
- TP asked whether we had news concerning the IPAC13 students' grants => EM to follow this up.
- WH is absent due the 80th birthday of Albert Hoffman => Happy birthday Albert!
- SL meeting:
- On 24/03 => Accelerator consolidation full-day review.
- On 12/04: LIU day.
- Staff children for 1 month.
- LMC and IEFC meetings will take place on Wednesday afternoons every second week (alternating) and the Friday mornings will be dedicated to LS1 follow-up (alternating between injectors and LHC).
- Review of LHC and injectors upgrade planned around September 2013:
- We should not reach the 400 fb^-1 before 2020 as the experiments (tracker) will not be able to digest that (the ~ 400 fb^-1 limit is similar to the one of the triplets).
- Goal is to review the plan and see what we really gain by major changes and long stops compared to minor changes and small stops.
- LHC open days: 27-30/09/2013.
- Impedance lab (8-R-006) + discussion about budget for impedance measurements. - We have already a network analyzer (from Christian Carli) and JosephK found already a 500 GHz/sample oscillo => We are on the good path!
- LHC Machine Protection (MPP) workshop, Annecy, 11-13 March 2013: https://indico.cern.ch/conferenceDisplay.py?ovw=True&confId=227895.
- CollUSmeeting => Talk by NM on HL-LHC collimator scenarios: some impedance considerations.
- Discussions with Rhodri for SC workshop and the involvment of BI. Also for HL-LHC impedance studies for BI.
- Bad news: After 2 years with us, AlexeyB has to come back to FNAL on June 1st.
- BSRT results and heating of the ferrite (to ~ 600 deg) => One should try to measure the mu’ and mu” of the ferrite vs temperature between room temperature and say ~ 800 deg (or as proposed by FC, check/measure the Curie point) => To be followed up.
- FC reported some BSRT impedance wire measurements with foam => Very strong effect of the foam, which acts as a microwave absorber, very effiecient for mode suppression in bench measurements but absolutely not usable in vacuum (Picture). Measurements were made on the BSRT tank (without the mirror etc.) => ~ 35-40 cm diameter, 5 cm thick foam. The cut-off frequency should be close to 1 GHz. there is a resistive matching. BS commented that this foam may kill in fact the modes we want to measure. The goal was to show that the foam can be used to remove the undesired modes. To be followed up.
- ZS review with talk from CZ (slides from BS).
- RF prototype received with slots perpendicular to the beam (for mechanical reasons) => Discussions ongoing (meeting with Teddy Capelli (EN-MME) and Alexis Vidal (TE/VSC), JK, FC, OB), but it will be a nice exercise to measure and simulate this subject => To be followed up.
- Question from Mike Barnes about possible issues with SS magnetic balls in the MKI => To be followed up and answer to Mike before the end of this week => Should be no pb but we should carefully check (HugoD is following this).
- Discussion with BS, FC and AlexeyG to try ad review all the techniques available to damp modes and compare them not only on the basis of the damping of the mode but also for the subsequent heat transfer => Would be a very interesting study.
- VittorioV will come to CERN on 18-22/03/13 and 25-26/04/13 to discuss in particular the Spring 2014 impedance workshop (which he would like to organise in Erice).
- Info from HugoD => Every couple of weeks CERN organises a Google+ hangout to interact with the public at large to discuss topics regarding the LHC/CERN/physics. Tomorrows one is concerning the long shutdown of the LHC and they're in desperate need of accelerator specialists for the event! It runs from 16.30-18 tomorrow (Thursday) afternoon, and all you need is either a webcam, or to join one of the other CERNies in the CMS centre (by LEIR) or near R1 => Please contact Hugo if you're interested and he'll forward you some more details.
- TP mentioned the opening of a new PHD position at Manchester to work on beam-beam effects for HL-LHC and LHeC.
4) Impedance localization update for PS, SPS and LHC: Part 2/2 (NB): pdf
- As there were new people today, NB briefly reviewed the first part of the talk he gave during the last meeting.
- EM reminded the 2 comments/suggestions: 1) put a table below the nice plots to see what is expected for the impedance value and what is deduced from the measurements; 2) check if imposing more constraints in the model by introducing the impedances we know (or we think we know) can help.
- Comment from AlexeyB to have an idea about the head-tail phase shift. Discussion about the possibility to make this measurement for mode 0 or 1. According to AlexeyB, the accuracy of this measurement is linked to the distance from stability: if we are too far from stability then the signal to noise ratio will not be good whereas if we are close to stability it will be much better but more dangerous => A trade-off needs to be found.
- Reminder: All measurements have been done with transverse damper off.
- LHC measurements:
- 2h MD time, Single bunch in beam 1 and 2, excited with an AC dipole.
- 3 meas. done with TDI IN and OUT => Fills # 3338, 3339 and 3340.
- Acquisition with both BPM system and ADT.
- Status of the analysis: the tune frequency is needed to correct the optics from the data measured at the AC dipole frequency: AC dipole tune (0.32) and free oscillation tune (~ 0.308).
- The vertical tune shift with intensity looks puzzling. More checks needed.
- Good agreement between accuracy expectation and measurements, but need to quantify the impedance now.
- Conclusion and overview:
- Better understanding of the major constraints in the impedance localization measurement.
- PS measurements are well between error bars but reconstruction is not straightforward.
- SPS measurements are still ongoing, especially for Q20.
- LHC measurements for LHC have still to be analysed in detail, especially to understand the puzzling tune behaviour.
- Clear simulation plan identified.
- Measurements in RHIC on 14-27/04/2013.
5) Review of the 2012 activities and current plan for the 2013 ones for SC (FS): pptx
- Review of 2012:
- General Plan => Main goal was to take data from all the machines before the LSD (for SC code benchmarking , to understand the relevant resonances without and with resonances) + PTC-ORBIT understanding/simulations etc. with SashaM (at CERN) + Re-start international collaboration
- Highlights:
- PSB => ElenaB and VincenzoF:
- Many MDs at 160 MeV (Linac4 injection energy).
- Ex. of a nice result with longitudinal losses due to 2Qy = 9 resonance crossing when the QNO correctors (used for 1/2 integer resonance compensation => Reduce the strength of resonance but keep the tunes ~ the same) are switched off.
- Tune footprint evolution vs. time.
- Study of the integer resonance (Qx = 4) effect => Measured horiz. norm. emittance vs. time over ~ 150 ms compared to simulations over ~ 100 ms.
- According to SimoneG, the fast wire meas. precision is few % in relative value.
- PS => RaymondW:
- Study of the 4th order resonance Qy = 0.25 to see if it is excited only by space charge (as it was not seen in some previous measurements by AlexanderH with a low intensity beam).
- Nice plots of intensity vs. time for different space charge tune spread.
- Nice plot of the vertical growth vs. SC tune shift on the long (1.2 s) injection plateau => ~ 5-10% at ~ 0.30 SC tune spread and ~ 30% at ~ 0.40 SC tune spread. In parallel to this one should also check the amount of beam losses.
- Very nice plots of compensation of 2Qx + Qy = 1 at 2 GeV:
- Without compensation, crossing the resonance from left to right or or from top to bottom, does not lead to the same result and therefore the 2 cases were studied.
- Using the model of the machine and performing simulations, some strengths of 4 skew sextupoles were predicted to compensate the resonance. Using these vales in the machine indeed considerably reduce the strength of the resonance => Congratulations! As often seen is such a case another resonance (3Qy = 1) is excited. It could be then also reduced
- SPS => HannesB:
- Studies performed on Q20 mainly with a single bunch and with many bunches (50 ns).
- Main message: Brightness achieved in SPS similar to LIU requirements! Beam also injected into the LHC for MDs.
- Study of blow-ups (in H and V) close to integer and emittance growth as a function of time (over 10 s).
- Simulations studies:
- Convergence studies and basic version of the lattice (no higher order multipoles apart from chromaticity sextupoles) done.
- Plan for the next steps.
- Collaborations:
- GSI => Started in December 2011, the GSI retreat, then PS MDs, visit to GSI to install PTC-ORBIT, etc.
- FERMILAB:
- 4 month visit.
- Frozen SC model in MADX already benchmarked.
- Micro-scale instability in ORBIT confirmed by experts and under study.
- Implementation at CERN of the SYNERGIA code as an alternative PIC code.
- Plan for 2013:
- Main goal of 2013 is to understand the experimental results with simulation.
- SC-13 workshop in April: http://indico.cern.ch/conferenceDisplay.py?confId=221441.
- A full code benchmarking is planned in the coming months => Helped by the SC-13 workshop in April and the following week with Jeff, Leonid and Eric to discuss all simulation issues and possible mitigations.
- After the SC-13 workshop => Decide how we should proceed with our simulations.
- Continuation of the various collaborations: SNS, GSI and Fermilab.
- Leonid could be the right candidate to spend some time at CERN in the future.
- Action FS: Check (asap) all the LIU requests and deadlines from PSB, PS and SPS linked to space charge and update them (if necessary) in agreement with all the involved/responsible people to set up a realistic plan (if necessary).
6) Actions to be taken for the next meeting
- Old actions.
- New actions:
- Action 1 (FS): Check (asap) all the LIU requests and deadlines from PSB, PS and SPS linked to space charge and update them (if necessary) in agreement with all the involved/responsible people to set up a realistic plan (if necessary).
7) Miscellaneous
- Deadlines and important dates for ICE.
- The next (77th) meeting will take place on 27/03/2013 => Agenda:
1) Lessons from 2012 as concerns the OP support (How can we prepare ourselves better for 2015: responsibilities, communication outside ICE or ABP, quicker answers, follow-up of the fills, data logging, post processing, for LHC but also the other machines etc.? => everybody).
- See preliminary agendas for the next meetings.
- See List of Actions.
Minutes by E. Metral, 27/02/2013.