Minutes of the HSC section

Transcription

1 Minutes of the HSC section 49 th meeting on Monday 22/06/2015 (14:00, 6/R-012) HSC members: Olav Berrig (OB), Christian Carli (CC), Elias Metral (EM), Giovanni Rumolo (GR), Frank Schmidt (FS), Elena Wildner (EW), Elena Benedetto (EB), Michael Bodendorfer (MB), Kevin Li (KL), Tatiana Pieloni (TP), Benoit Salvant (BS), Guido Sterbini (GS), Daria Astapovych (DA), Meghan McAteer (MM), Nicolo Biancacci (NB), Alexander Huschauer (AH), Giovanni Iadarola (GI), Adrian Oeftiger (AO), Serena Persichelli (SP), Tatiana Rijoff (TR), Letizia Ventura (LV), Claudia Tambasco (CT), Magdalena Kowalska (MK), Andrea Passarelli (AP), Annalisa Romano (AR), Michael Schenk (MS), Vincenzo Forte (VF), Javier Barranco (JB), Aaron Paul Axford (APA), Malte Titze (MT), Francesco Paciolla (FP), Mario Stefan Beck (MSB), Stefan Hegglin (SH), Alpo Valimaa (AV), Hannes Bartosik (HB), Lee Robert Carver (LRC). Present/Excused: OB, CC, EM, GR, FS, EW, EB, MB, KL, TP, BS, GS, DA, MM, NB, AH, GI, AO, SP, TR, LV, CT, MK, AP, AR, MS, VF, JB, APA, MT, FP, MSB, SH, AV, HB, LRC, XavierB, Na Wang, LottaM, Themistoklis Mastoridis, Philippe Baudrenghien, WolfgangH, RamaC, AlexejG, YannisP. 1) Newcomers / visitors - None. 2) Comments on the minutes of the previous 48 th meeting + Actions - No comment. 3) General infos - SL meeting => Short SLM as we had the ABP info meeting. - For supervisors: be careful with extension of students as COAS if they have a lot of vacation which would cover most of the COAS extension => Encouragement to the students to take all their vacation before the end of their contracts. - LBOC meeting with talk in particular from LeeC on chromaticity => Several actions and recommendations made. To be continued. - Task 2.4 meeting on the impedance of the Crab Cavities => To be finalized during the next

2 meeting on 01/07/ MSWG with i) talk from SerenaP on the PS tune shifts (good agreement now reached at 2 GeV. Next step: understand why the impedance increases with chromaticity, which has been confirmed). Reminder: SerenaP s farewell lunch on Friday. Many thanks for all SerenaP and good luck in the US!; ii) PS longitudinal coupled-bunch instability by LetitziaV. - Discussion with Andrea Latina about his recent work on a space charge code => He will present this work at some point to the SC WG. - Impedance meeting with talk by SerenaP on PS new elements (BGI and SMH42), NaW on impedance calculations for the new LHC triplet shielded bellows and the changes linked to 5th axis in LHC, AlpoV on update on SPS Wire Scanner Prototype Measurements (and proposed solution through feed-throughs and all-modes coupler). 4) Brief performance reports for the different machines - PSB (ElenaB) - A busy week for the PSB, after the TS. We started well as the PSB was back on its feet with beams happily running in the machine by 11 am. Unfortunately, we soon realized together with the BI experts, that the wire-scanner in ring 3 vertically, the one replaced during the TS, was broken. On Wednesday, with LHC in TS, experts could focus on 3 dedicated MDs: 1) A dedicated MD for the RFQ in Linac2 to check if the transmission could be improved. In the end, the Linac2 team could only gain in transmission (up to 5-6 ma) in conditions that are not very suitable for operation (significant beam loading, tank3 saturation, unstable RF conditions). The nominal settings run at the moment is still considered to be the best option. 2) A dedicated MD to investigate the position fluctuation, present since the beginning of the year, in the beam position monitors at the end of the BI line. The stability of these pick-ups is very important for the PSB operations/mds. It turned out that the BPMs are very sensitive to the bunching of the Linac2 beam and more work is needed to have the equipment robust against the L2 beam bunching. 3) A dedicated MD on the TFB to investigate the random losses in ring 4 which are quite disruptive for the PSB operations. A lot of work was done, few hardware parts were changes, but the losses are unfortunately still there. Some additional useful feedback may come from the Finemet MDs currently carried on in the PSB. Generally the issue is closely followed up by the TFB team in conjunction with the PSB crew. - PS (GuidoS)

3 - See picture: => MTE extracting 1.4e13 ppp. - This week was marked by the TS and the SPS scrubbing run. All required beams were delivered: LHC25 72b high intensity (2e11ppb), LHC50 36b, LHC50 6b, LHCINDIV and AD. "Beam for physics was sent to TOF, the EAST Area and SPS (from Saturday). During the TS the 68H wire scanner was installed again (Reminder: 68H is very interesting because it will give the possibility to measure bunch by bunch, thanks to the high-bandwidth cable). The bumper 14 power supply was exchanged by the bipolar spare for the MTE extraction and the intervention on the PFWs (FNI, FNP, DNI, DNP) power supply inductance was finished. The changes on the BSW14 and PFWs have provided very good results on the MTE beam, the island capture is stable and the extraction on the outer side of TPS15 is now working. Optimization is ongoing. - SPS (HannesB and/or BenoitS) - See picture => scrubbing run: - Started scrubbing on Tuesday evening until Friday. - When they stopped for MKP heating, some dedicated MD could be used (in the PSB for instance, which helped them to identify an issue with the BPM). - An estimation of the contribution of uncaptured beam has been made (~ 4%). - It was a good week for the SPS devoted to the technical stop, to a scrubbing run and to HiRadMat extractions for the HRMT-22 experiment. North Area physics restarted on the weekend. - During the technical stop the firmware of the rotational wirescanners was successfully updated, the COLDEX bypass was re-installed with new Y-chambers and the SLAC rotatable collimator was installed. The endoscopy of sector 101 (where a horizontal aperture restriction is encountered with LHC beams) revealed traces of beam impact on the vacuum chamber in the bending magnet LHC and HL-LHC (EliasM) - Delay with the scrubbing run, which should start tomorrow (still tbc)... - LEIR (MichaelB) - Excused.

4 5) Summary of 1-beam and 2-beam stability predictions for LHC in 2015, from injection till collision => Tune footprint at LHC injection with space charge and octupoles (FrankS): and st 14 slides as reminder. - Slide 15 => parameters used and then results presented in the slides after with space charge only, space charge and octupoles (LOF = as beginning of 2012) and space charge and octupoles (LOF = as end of 2012 and now). Also +/- 1 A and +/- 3 A in the octupoles discussed. - It can be seen that with LOF ~ - 1 A there is a significant reduction (compensation) between space charge and octupoles for the particles amplitude below ~ 3 sigmas, as seen on slide 54 of (where a distribution up to 3.2 sigmas was considered, whereas FrankS considered here particles up to 6 sigmas). Please note that the beams sent to the LHC are cut at ~ 3 sigmas in the SPS and it was checked in the past (2012) that there was not much tail repopulation on the flat-bottom of the LHC (discussion with VerenaK, 25/06/2015) => One should redo these plots with particles up to ~ 3 sigmas only (or do not consider in the plots shown here the particles above ~ 3 sigmas). - In his second file ( FrankS made a detailed scan in the octupole current, from 0.4 A to 2.3 A, where the resulting tune footprint is superimposed to the one from space charge only (which looks that the tune footprint from BB, BBHO + BBLR! => To be checked). 6) Report on NAG: Numerical Algorithms Group (FrankS): - There is no request from the section => Do we all agree? 7) Transverse emittance growth due to RF noise in the Hi-Lumi LHC Crab Cavities (T. Mastoridis, California Polytechnic State University, San Luis Obispo, USA): - Themis and Philippe derived 2 nice formulas for the phase noise and the amplitude noise. - The growth rate dependence on bunch length is opposite for the 2 (which was also checked with HEADTAIL simulations): - Phase noise: it is maximum for short bunch length and 0 for long bunch length. - Amplitude noise: it is 0 for short bunch length (and this explains why this is/was not a worry for certain machines) and maximum for long bunch length.

5 => Amplitude noise from the Crab Cavities is the issue for HL-LHC. - The target of ~ 5% emittance growth / hour is linked to the fact that it is what is expected for the IBS rate. - Chromaticity: for Themis studies, below ~ 10 units is something not too high. Furthermore, Themis added that the higher the chromaticity the smaller the emittance growth (seems to be due to some sharing between transverse and longitudinal. Still to be looked at in detail). - The ADT is less efficient in the tails (as the distribution enters in the averaging). Furthermore, the ADT excite also in the tails (in opposite direction in head and tail due to the effect of the long bunch => See slide 10 on the left). - Reminder: factor 2 between the amplitude and noise because the sampling is higher by a factor 2 for the latter. - They used 3E-3 for the rms spread. As a first step this spread was introduced in HEADTAIL by playing with the octupoles to approximate the beam-beam tune spread. - Summary: All this need to be measured in the SPS and they could inject deliberately more noise in the Crab Cavities to see something if needed (as there is already quite an important natural emittance growth in the SPS). - Conclusions - Future steps: look at distribution change (not just emittance). - Conduct two-beam simulations to estimate possible reduction of phase noise effect due to beam-beam (with ABP) => Ongoing discussions with beam-beam team (see below). - A wideband transverse damper ( 2 GHz) would help reduce the amplitude noise effects and thus relax the LLRF requirements - Request from Themis and Philippe to ABP - A past work from YuriA (FNAL) indicated a factor ~ 3 improvement with beambeam when the pi-mode is outside of the incoherent spectrum but it seems that with the mode inside the bunch spectrum, this factor 3 could be lost again (this is currently studied in detail by the beam-beam team). PhilippeB mentioned that YuriA s work was done for dipole modes and here this is not the case. => So what Themis and Philippe did seems to be the best approach for the moment. More info will come from the beam-beam team during this summer. - PhilippeB mentioned that all bunches will see the same noise => It is very low frequency and therefore this is where we will have all the gain. - Question from AlexejG: Would we gain something if Qloaded would be bigger? This answer is that no effect is expected.

6 8) Actions to be taken for the next meeting - List of all actions: 9) Miscellaneous - The next (50 th ) meeting will take place on 29/06/2015 => Agenda: 1) General info and follow-up (EliasM) 2) Brief performance reports for the different machines (PSB, PS, SPS, LHC and LEIR) => With ideally a picture of the week! - Important events and dates for HSC: - Preliminary agendas for the next meetings: - List of actions: - Web site: Minutes by E. Metral, 25/06/2015.