Minutes of the ICE section
85th meeting on Wednesday 26/06/2013 (08:40-10:30, 6/2-004)
ICE members: Adrian Oeftiger (AO), 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), 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: AO, BS, CZ, DB, DA, EM, EW, FS, GI, GR, JB, JLN, KL, NB, NM, OB, SP, SRF, TP, WH, XB, Alexey Burov, Andrea Mostacci, Guido Sterbini, Simone Gilardoni.
1) Newcomers / visitors
- None.
2) Comments on the minutes of the previous 84th meeting + Actions
- Answer to Action 14 (Is a minimum separation of 10 sigmas OK / enough for the new IR8 crossing schemes at injection?) by WH => Slides:
- Reminder: In IP8, there is the superposition of the crossing angle and the spectrometer => Good for the good spectrometer polarity (1 crossing) but bad for the bad polarity (3 crossings).
- Summary: for the critical encounters, the 2012 separation (with 50 ns, 2.5 microm) is recovered (with 25 ns, 3.75 microm and new separation proposed by StephaneF of 3.5 mm and vertical angle).
=> Should work most likely, provided:
- Emittance for 25 ns is not larger than 3.75 microm.
- No additional surprises for 25 ns spacing.
- Reminder on the 10sigma value:
- The criteria of 10sigma should be taken only as a preliminary assumption on a very early design stage, applicable only for low beta insertions and alternating crossing and a static case (and the present machine).
- Other effects but the separation such as number of encounters, intensity, presence of other non-linear fields, SB coupling, noise, tune (!), interplay with impedance, e-cloud a.m.m. have to be taken into account for a reliable estimate and evaluation.
- Any design has to be accompanied by tracking and analytical estimates like the ones developped with Dobrin Kaltchev.
- Expect: as large as possible !!
- So for a first target one should aim for at least 10sigma in any design, but especially for higher intensities this should not be enough in the presence of many LR encounters.
3) General infos
- No particular comment from anyone.
- Lionel Prost (FNAL) was at CERN for one day on Monday 17/06/ 13 and gave a talk at AP forum (Project X overview).
- The RLIUP will be moved to another date (not 8-10/10/13) => Still under discussion.
- SL meeting:
- Reminder about the request of information concerning Knowledge Transfer made by the KTT group (Tracking KT through Teaching, Technical Trainings and Consultancy) => Form to be filled (which I sent at some point).
- From the Research Board => BASE approved. BASE is a new experiment (line from AD).
- MTP:
- AWAKE facility spread over 5 years instead of 3.
- CENF: Money for studies of the transfer line and of the extension of the experimental North Area.
- Conceptual Design of a new frontier high-energy hadron machine to be ready by 2017.
- PS 40 MHz status: A major damage was discovered when the amplifier and cavity were connected to the spare HV power converter for testing on 14 August 2012. The RF low level measurements have shown a frequency displacement of the cavity resonance by 600 kHz, likely something has happened inside the cavity. The maximum tuning range is 200 KHz and the cavity needs to be opened.
- MTE HW changes approved by IEFC.
- High-bandwidth feedback meeting from WolfgangH on FR 21/06 => Discuss the motivations of the high-bandwidth feedback.
- Impedance meeting on MO 24/06 => Good model now of the PS kicker (with segmentation) from MauroM with CarloZ.
- News about satellites (from PS to LHC ) and info from SteveH:
- StephaneF proposed to correlate the fact that we have 25 ns satellites sent from the injectors (or not) with our unexplained instabilities => EM contacted SteveH who answered that Lene Norderhaug Drøsdal tried to correlate this with losses in the past and she found no convincing correlation => We should try and correlate this time no woth the (injection) losses but with instabilities. Here is a summary of the actions of satellites (many thanks SteveH!):
- 2012-10-12 12:24 - At the request of Mike Lamont, SteveH switched on the enhancement of satellites.
- 2012-10-19 pm - At the request of the Mike Lamont, SteveH switched it off.
- 2012-10-25 12:27 - At the request of the LHC Coordinator, SteveH switched it on again, but the poor initial condition already produced strong satellites.
- 2012-10-25 20:42 - It was switched off by the PS OP crew.
- 2012-10-26 ~13:00 - SteveH found and corrected the underlying problem that caused the previous attempt to be aborted.
- 2012-10-27 10:16 - It was switched on by the PS OP crew and it remained untouched for more than two weeks.
- 2012-11-12 ~10:15 - With the agreement of the LHC Coordinator, SteveH switched it off, which is how it remains.
- New request from Witold Kozanecki:
- Reminder: Due to the beam-beam deflection (in fact 2/3 from deflection and 1/3 from dynamic beta) generating a systematic orbit deformation at the interaction point, the luminosities had to be re-normalised by 1-2% .
- The next step is to check the effect of the wake fields => Question: What is the kick at the TCT and the orbit displacement at the interaction point (ATLAS)?
- Transverse impedance finite length => Promising results from NB.
- TCTP => Visit yesterday and meas. could start next Monday and for the week.
- Talk by KL at the optics workshop on "Observations on dispersion (2011-2012)".
4) Main 2013 MD results / issues on collective effects in the PSB, PS and SPS (GR): pptx
- Some studies have already been reported in detail during some ICE meetings => Not discussed today.
- Most of the results are still preliminary!
- PSB:
- Transverse instabilities
- C370 => Effect of single and double RF, C04 voltage, chroma, transverse damper gain.
- C480 => Effect of double RF.
- Data recorded with Q-meter and TFB PU => Nice movies.
- PS:
- Transverse feedback system:
- Damp the HT instability at injection.
- Damping of injection oscillations.
- Damping of H (ecloud?) instability at 26 GeV/c => Delayed.
- Study at transition with a single bunch 45E10 p/b with ~ 0.2-0.3 eVs => Different frequency seen compared to nTOF (with ~ 800E10 p/b with ~ 2.5 eVs) but the bunch length is different! The feedback was found ineffective for this kind of instability.
- LCBI and feedback:
- Spare 10 MHZ cavity C10-11 used as a kicker cavity for the feedback.
- Many studies already reported during recent talk of Mauro Migliorati (http://emetral.web.cern.ch/emetral/ICEsection/2013/2013-06-12/ICE_20130612_Coupled_bunch.pdf).
- Goal was to extract relevant voltage requirements and estimate performance of new longitudinal damper with wide-band kicker cavity (installed during LS1).
- Ecloud meas.:
- Before bunch rotation => Main contribution to the measured pressure rise in drift section.
- Possible mitigation strategies => Lower RF voltage, double-bunch rotation, shorter trains (60 or 48 bunches).
- No observed ecloud before bunch rotation with 50 ns.
- SPS:
- RF MDs:
- fs2 vs intensity as a reference impedance meas. before LS1 (single bunch, Q26).
- Spectra of long bunches with RF OFF in Q20.
- SB stability in single and double RF systems with Q20 and Q26.
- Nice beams produced by SteveH (with the new C16 knob in the PSB) to achieve beams with the same longitudinal emittance but different intensities (2E10 and 8E10).
- Comparison with 2008 shows that longitudinal impedance is reduced (serigraphy of MKEs).
- More studies ongoing on the identification of the 1.4 GHz impedance source.
- Transverse MDs:
- TMCI threshold with Q20 and Q26:
- Scans in chroma, RF voltage (always in double RF with voltage of 800 MHZ at 10% of 200 MHZ). Data recorded with Qmeter, BBQ, BCT, WCM, wirescanner, headtail monitor, PS longitudinal emittance, PS BCT => Many data available to be compared to simulations.
- Nice intensity threshold proportional to longitudinal emittance for Q26 => As expected from a broad-band resonator in the long-bunch regime.
- For Q20, an "island" of slow instability observed for intermediate intensity and small longitudinal emittance (different from Q26) => Is is a sign of mode-coupling decoupling, as observed in the past with Q26?
- Nice movies.
- Switching ON the transverse damper did not improve the situation.
- Doublet 25 ns beam => Potential of becoming the future scrubbing beam.
- High-bandwith transverse damper:
- Driven motion studies.
- Feedback studies of naturally unstable or marginally stable beams (making the beam unstable with negative chroma).
=> Many nice studies to be studied in detail!
5) Transverse impedance localization results from BNL (NB): pdf
- AGS:
- Impedance measurement from tune shift vs intensity => Zy ~ 1.3 MOhm/m (+- 0.1) at extraction. The machine is very stable and therefore measurements of very small tune shifts are possible.
- Meas. seems consistent with a longitudinal impedance Zl/n measured in the past of ~ 10 Ohms, assuming that it is mainly due to resistive wall.
- RHIC:
- Blue beam => Zx = 9.5 MOhms/m (+- 1.8) and Zy = 8.8 MOhms/m (+- 1.4).
- Yellow beam => Zx = 3.9 MOhms/m (+- 1.3) and Zy = 3.0 MOhms/m (+- 0.8) => Why are the impedances much smaller than for the blue beam?
- Meas. of phase advance slopes:
- The loss of accuracy in the measurement is mainly due to: i) short coherent time (< 500 turns) and ii) high NSR.
- Analysis ongoing.
- Outlook:
- AGS: H-plane will be measured as well (expected less impedance).
- RHIC: An estimation of some (big) impedance source could help understanding which impedance signal we want to localize. A better adjustment of chromaticity could help increasing the resolution.
6) Actions to be taken for the next meeting
- Old actions.
7) Miscellaneous
- Deadlines and important dates for ICE.
- The next (86th) meeting will take place on 03/07/2013 => Agenda:
1) Brief reports of the 4 WGs (by the WG leader or replacement) => Plan, activities, deadlines, issues, etc.: BB, SC, EC, IMP,
2) Effect of transverse impedance on luminosity measurements (EM).
- See preliminary agendas for the next meetings.
- See List of Actions.
Minutes by E. Metral, 01/07/2013.