Minutes of the HSC section. 5th meeting on Wednesday 26/02/2014 (09:00, 6/2-004)

Transcription

1 Minutes of the HSC section 5th meeting on Wednesday 26/02/2014 (09:00, 6/2-004) 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), Adriano Garonna (AG), Meghan McAteer (MM), Nicolas Mounet (NM), Carlo Zannini (CZ), Nicolo Biancacci (NB), Xavier Buffat (XB), Alexander Huschauer (AH), Giovanni Iadarola (GI), Adrian Oeftiger (AO), Serena Persichelli (SP), Tatiana Rijoff (TR), Letizia Ventura (LV), Magdalena Kowalska (MK), Andrea Passarelli (AP), Vincenzo Forte (VF), Danilo Banfi (DB), Javier Barranco (JB), Joseph Kuczerowski (JK). Present/Excused: OB, CC, EM, GR, FS, EW, EB, MB, KL, TP, BS, GS, DA, AG, MM, NM, CZ, NB, XB, AH, GI, AO, SP, TR, LV, MK, AP, VF, DB, JB, JK, LottaM, MauroM, HannesB. 1) Newcomers / visitors - Reminder: Lotta Maria Mether started as FELLOW in January in the ABP-LAT section to work on the fast beam ion instabilities for future electron machines under the supervision of GiovanniR. She should also work on e-cloud for the CERN accelerators. 2) Comments on the minutes of the previous 4 th meeting + Actions - URGENT => Code specs please! Many thanks for HEADTAIL but where are the others (PyECLOUD, COMBI, etc)? - List of actions: 3) General infos - No particular comment from anyone. - SL meeting: - Possible micro-open days at the occasion of the CERN 60 th anniversary. - MiguelM has been appointed LS2 coordinator.

2 - DelphineR send 1 st invitation for ABP group info meeting. CarloZ will give a short summary for SPS impedance model. - Cooling for TDI will finally be installed and could be activated if needed. 4) A first trial to reduce collimation impedance by playing with the IR7 optics (NicolasM): - NicolasM presented his idea (and his initial test) to play locally on the IR7 optics to try and decrease the impedance there. - Until now (to my - EliasM - knowledge) the impedance has been optimized by looking at the scaling of the resistive-wall impedance in the plane of collimation. The new idea here is to optimize also the other plane. - The procedure adopted was to minimize an impedance scaling factor in IR7 (based on the two previous formulae), which can be done as a matching in MAD-X using macros => Playing with the quadrupole strengths of all MQTLI, MQTLH and MQW (A and B). Optics used = standard v6.503 (55 cm beta*). - Many matching conditions were needed: ~ 48, done in several steps. - The preliminary result is that we can gain up to ~ 15% on the total impedance budget at high frequency. - Reminder: only contributions of collimators studied but other effects not included yet. - Next step: discuss with the optics and collimation experts, as this first trial was impedance driven. 5) Simulations of high bandwidth feedback systems (KevinL): - KevinL reminded us that this is the work he did during his 3 rd year as COFUND fellow that he spent at SLAC. He also shared with us his experience, which could be useful for the future COFUND. - KevinL discussed first the principle of a feedback system and explained the role of the bandwidth. - KevinL then discussed realistic feedback systems and the implementation in HEADTAIL. - Notion of stability diagram for the beam but also for the controller.

3 - A realistic feedback system is bandwidth limited, which means that the amplitude and phase responses are not flat => Trade-off between increasing bandwidth and noise. - A realistic feedback system often incorporates DSP filters to correct for phase errors and provide some means of noise filtering. Might be well matched for low Qs synchrotron sidebands but problem for high Qs synchrotron sidebands. - Modeling of a feedback system - Block diagram => Formal solution => Z-transform of the solution. - Gain and stability => OK for SPS Q26 optics but issue found and understood for Q20 optics (good agreement between a simple model of the feedback without impedance etc. and HEADTAIL simulations). The problem was due to the fact that the FIR filter has been designed for Q26 and not for a high Qs as for Q20. - The numerical HEADTAIL feedback model - Pick-up transfer function and noise, - FIR and IIR filter coefficients, - Kicker transfer function and noise. - KevinL created a class to be as modular as possible. - Application of this feedback model to transverse mode coupling instabilities - For both SPS Q26 and Q20 optics. - Detailed studies / scans: gain and bandwidth. - Noise and saturation - Saturation maps - Kicker signal - Capture maximum kicker strength - Repeat for a series of cloud densities, each, for a series of gains and plot each point over the cloud density gain plane - Cut resulting graph at saturation level - Conservative approach but allows for wide range parameter studies to obtain a big picture

4 - Depending on the saturation, we can have a larger or not stability region => Saturation maps are really giving indications on where we expect instabilities. - Next step => Review of bunch-by-bunch transverse feedback models in HEADTAIL (NicolasM) and COMBI (XavierB). 6) Actions to be taken for the next meeting - List of all actions: 7) Miscellaneous - The next (6th) meeting will take place on 05/03/2014 (from 09:00 till 12:30) => Agenda: 1) Special meeting devoted to follow-up of the LHC performance limitations review during run I to prepare the LHC re-start in Note: As of 05/03/2014 (and until 16/12/2015), the usual room will be 6/R-012 but it will not be available on: - 26/03/2014 => Room will be: 6/ /04/2014 => Room will be: 6/ /06/2014 => Room will be: 6/ /09/2014 => Room will be: 6/ => This information can also be found on the web site: - Important events and dates for HSC: - Preliminary agendas for the next meetings: - List of actions: - Web site:

5 Minutes by E. Metral, 18/03/2014.