Minutes of the ICE section
89th meeting on Wednesday 21/08/2013 (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, Berengere Luthi, HannesB, GuidoS, SimonW, JosephK.
1) Newcomers / visitors
- Johannes HERBST (short-term student from Vienna University of Technology, with M. Benedikt) will join our team to work on impedance measurements on Monday 16th September and stay for 8-10 weeks.
2) Comments on the minutes of the previous 88th meeting + Actions
- No comment.
3) General infos
- No particular comment from anyone.
- SL meeting:
- M. Benedikt should be the study leader for future accelerators (mainly the 80km tunnel) to integrate requests for hadron and lepton machines.
- Staff Association is preparing a survey for the 5yearly review.
- Space-management: Any damage to CERN property should be reported to GhislainR, staff should feel responsible to report this.
- New CO building opposite the CCC: The company has liquidity problems, work has stopped for a month.
- Issues with the "new" CERN website => Please forward me any comment you would have as there are currenlty discussions at the BE department level.
- Indico site prepared, as forseen, for the LPL review of September => https://indico.cern.ch/conferenceDisplay.py?confId=267783.
- PS TFB kicker (97) measurements last week by F. Blas, J. Kuczerowski and G. Sterbini => To be discussed next week (GuidoS).
- Discussion with F. Blas on the necessary bandwidth to damp an instability at a certain frequency? => Action 1 below.
- Anthony Hawkins (PHD student from Lund university => Lower right in the picture) is looking to get some experience in Hardware/Accelerators and would love to learn more and help in the ongoing accelerator work. The ideal project for him would be 3-6 months from October (due to personal constrains he would prefer not to be at CERN for the whole time but perhaps could come for a month, go home for a month and then come back, or something to that extent) => Anybody interested? Please tell me asap.
4) Recommendation for the SPS high-bandwidth kicker (CZ): pptx
- CZ first showed some slides on kicker impedance calculation from the high bandwidth damper system review held on 30/07/2013:
- Slotted kickers (studied by INFN team) => Better suited for the high-frequency range. Several options have been studied (slotted-waveguide, slotted-ridged, slotted-coaxial).
- Stripline kickers (studied by LBNL team) => Better suited for the low-frequency range.
- Note that ferrite kickers were not discussed as certainly the rise time would be much too long.
- Final slide is the recommendation for the SPS transverse impedance budget:
- The effective impedance of the new wideband kicker should be compared with the effective impedance of installed devices.
- The total measured effective vertical impedance of SPS is around 18MΩ/m. Based on 3D simulations, coaxial wire measurements, beam induced heating measurements and history of the measured effective vertical impedance the kickers are the most important contributors (around 7MΩ/m).
- Presently there are 19 kickers installed in the machine, an average contribution per kicker of ≈ 0.37 MΩ/m.
- The beam coupling impedance of the new wideband kicker should not exhibit narrow resonances and must contribute by less than the average contribution per kicker, i.e. ≈ 0.37 MΩ/m. Preferably the beam coupling impedance should not exceed about 1% of the total SPS impedance, i.e. ≈ 0.18 MΩ/m.
5) Benchmarking CST impedance simulations and application to the BGV project (Berengere Luthi): pptx
- Berengere Luthi is Summer student with BS and CZ.
- Berengere compared the 2 CST solvers (Eigenmode and Wakefield) for both longitudinal and transverse impedances of a simple cavity:
- Reminder about the factor 2 difference between LINAC and CIRCUIT (convention): 1 LINACOHM = 2 CIRCUITOHM.
- Strategy suggested:
- Wakefield values should be used as references when the unit Omh is used.
- With the Eigenmode solver it is better to talk about LinacOhm or adapt the value to obtain Ohm.
- Longitudinal studies (changing the length and radius of the cavity, changing conductivity, studies on both magnitude and Q, first mode only, first check with ferrite materials):
- The ratio of the shunt impedance with Eigenmode to the shunt impedance with Wakefield seems to be converging to a ratio close to 2 (as expected if Wakefield is using the CIRCUIT convention and Eigenmode the LINAC one) and ~10% error is still obtained even though the wake decayed by a factor 100. When the wake field decayed less (as for instance when using a higher conductivity), the ration increases.
- ~ 10-20 % error in the Q value.
- Using ferrite, the orders of magnitude between the two solvers are the same, but a significant difference in the Q value is revealed (50%). R/Q looks reasonable but which code should we believe? => Further checks with HFSS. CZ commented that Wakefield has be checked a lot with ferrite (e.g. compared to Tsutsui etc.) => The eigenmode solver should first be checked as carefully as done in the past with the Wakefield solver.
- Transverse studies (studies on both magnitude and first mode only ):
- Need a way to know which modes are really transverse modes => Should be a function of d^2.
- ~ 10% error in impedance and ~ 20% error in Q.
- Application to the BGV project:
- BGV = Beam Gas Vertexing => The goal is to provide another transverse emittance measurement in the LHC.
- The initial radius of 147 mm was reduced to 106 mm, which is much better.
- The influence of the length, taper and angle of the taper have been studied in detail.
- With the Steel/Copper structure, longitudinal and transverse modes seem to be under the acceptable limit => We are still waiting for the final structure to confirm these first studies.
- Typo on slide 26 => Frequency in GHZ should be replaced in fact by number of modes.
6) Brief reports of the 4 WGs (by the WG leader or replacement) => Plan, activities, deadlines, issues, etc.:
a) BB (TP):
- Tatiana: working on beam-beam impact on chromaticity in squeeze, adjust and stable beams. LHC note on measurements of beam-beam deflections during van der meer scans is ready for publication with J. Wenninger and W. Kozanecki (=> CERN-ACC-NOTE-2013-0006). A second one on MADx modeling and calculation of multiple IPs van der Meer scans is in preparation.
- Xavier (adjust and IP8 bunches), Danilo (Lumi data analysis ATLAS and in contact with LHCb) and Tatiana (squeeze data ) all working on data analysis for the review of september.
- Xavier: presented last beam-beam meeting some first studies with matrix model for beam-beam, impedance etc.
- Javier, checked 6D beam-beam lens finished. Writing relative documentation and prepare presentation for a future ICE meeting. Start looking into COMBI for implementing 6D beam-beam lens.
- We are waiting for the release of the new version of Sixtrack with crab crossing to perform DA studies for next LARP collaboration meeting.
- Werner at CAS and Tatiana will be absent again next week for same reason.
-WIth Ohmi-san, J. Qiang and S. Paret working on reproducing 2012 bunch shortening phenomenon on blown-up bunches. Work on-going.
b) SC (FS):
- Tough work on MPI and other code issues by Harry & Raymond.
- Check non-reproducibility of PTC-ORBIT by SNS team (very relevant >> indeed!).
- In-depth Benchmarking of CHEF code in SYNERGIA.
- SC benchmarking on 3 fronts!
- Progress on PS tracking and resonance analysis with Giuliano.
- Substantial code work to get MAD-X ready for SC tracking for real world examples
- Comment from EM: Concerning space charges studies (in fact coupled with the instabilities studies), do we foresee for instance to install some kind of very sensitive instrumentation to study in detail the evolution of the tune spectra with intensity and learn more on the effect of space charge on head-tail modes for instance (as done at GSI)? Furthermore, I think to remember that during the last space charge workshop we discussed the possibility to (re)-install for instance the quadrupolar pick-up to have a direct measurement of the space charge tune spread, which is the most important space charge parameter and which is usually not very well known... Will this be done? In the PS only? What about PSB and SPS?
c) EC (GR):
- PS: we are wrapping up all the information to write the the
part of the TDR concerning the electron cloud. This will include stuff on 1) the
measurements with the EC monitors, pressure measurements and RF voltage scans,
instability measurements with ad without transverse feedback system; 2) all the
simulation development that led to the possibility of simulating sections with
arbitrary magnetic field maps, the results of the simulation campaigns for the
main magnets as well as the drift sections, the simulation study of MU57 for the
installation of the new EC monitor, the evaluation of the expected stable phase
shift from simulations. Sergio has continued the simulations of the PS chambers
and he is also starting to write a note, which he will also use as project for
his graduation at the university of Zaragoza.
- SPS: no news, except that
the report from the reviewers of the HBWD has been released and they have
encouraged continuing the development, albeit some reservations on the choice of
the kicker and the possible interference between the existing damper and the
high bandwidth one. We'll meet with Wolfgang on 28 August to define the path for
the future work.
- LHC: Gianni has basically finished the scan of the
triplets and used the integrated results to compare with the experimental data
from heat load with both 25 and 50 ns.
d) IMPED (BS):
- Slides.
- Several systematic studies to understand better our simulation tools.
- Chapter 15 (of a High Lumi book) on Impedance and Component Heating written.
- Chapter on transverse impedance for the PS LIU TDR to be finalized.
- LHC ALFA detector => Good agreement between measurements and previous simulations.
- Comment from NM for the LHC impedance (work with MikhailZ): the geometrical wake of the collimators is important as it is equal to the resistive one when the half gap is 6 mm. This is due to the transition between round to flat (critical area already mentioned by AlexeyG in the past). Therefore, the transverse impedance could increase (still to be properly quantified) in fact during the squeeze. Current issue about wakepotential vs. wakefunction...
- A possible culprit for the 1.4 GHz line in the SPS longitudinal spectrum may have been identified by FritzC and Jose => Unshielded bellow. To be followed up.
7) Status of the work for the internal review on the LHC performance limitations during run I (on 25-26/09/2013) => All the speakers
- Meeting last Friday organised by NM => Things are progressing. Another meeting this Friday.
8) Actions to be taken for the next meeting
- Old actions.
- New actions:
- Action 1 ("instability and damper team"): Following a discussion with / request by F. Blas and following the recent work on the effect of a transverse damper on transverse coherent instabilities, can we give some recommendation on the necessary bandwidth needed to damp a transverse instability at a certain frequency? => Seems quite difficult question (depends on the type of instabilities, etc.) which we cannot answer now but which hopefully we will be able to discuss in the future => We should work in this direction.
9) Miscellaneous
- Deadlines and important dates for ICE.
- The next (90th) meeting will take place on 28/08/2013 => Agenda:
1) PS TFB kicker (97) measurements (Guido Sterbini)
2) Status of the work for the internal review on the LHC performance limitations during run I (on 25-26/09/2013) => All the speakers.
- See preliminary agendas for the next meetings.
- See List of Actions.
Minutes by E. Metral, 21/08/2013.
