Minutes of the ICE section

3rd meeting on Wednesday 28/07/2010 (08:40-10:30, 6/2-004)

ICE members: Benoit Salvant (BS), Christian Hansen (CH), Carlo Zannini (CZ), Diego Quatraro (DQ), Hugo Alistair Day (HD), Elena Benedetto (EB), Ewen Hamish Maclean (EHM), Elias Metral (EM), Elena Wildner (EW), Frank Schmidt (FS), Giovanni Rumolo (GR), Jean-Luc Nougaret (JLN), Kevin Shing Bruce Li (KL), Maria Carmen Alabau Pons (MCAP), Nicolo Biancacci (NB), Nicolas Mounet (NM), Olav Ejner Berrig (OB), Werner Herr (WH).

Present: BS, CZ, EM, GR, JLN, NB, NM, OB + Rama Calaga.

Excused: CH, DQ, HD, EB, EHM, EW, FS, KL, MCAP, WH.

1) Comments on the minutes of the 2nd meeting + Actions

- Comments: None.

- Actions: Still waiting for some contributions of the last round table.

2) General infos

- REMINDER (See minutes of the 2nd meeting):

- All the next ICE section meetings will take place on Wednesdays, every week, in room 6/2-004 (I reserved it until the end of 2011):

• 08:40 - 09:00 (20 min) => Closed part (only for the members of the ICE section) => General info, hot topics, etc.
• 09:00 - 10:30 (1h30 max) => Open part (with interested colleagues from other sections, groups etc.) => "Collective effects meetings" (replacing the "impedance meetings"), where "informal" presentations (in particular on impedances, space charge, coherent instabilities, ecloud and beam-beam) will be given and discussed in detail.

- When I will send the invitations each week, I will send only those to the 2nd part (starting at 09:00) and I will send them also to the LIS and LCU members and members of the "impedance team".

- However, the ICE section meeting will always start at 08:40.

- Some useful links to follow the LHC activity:

- LHC (and other machines) vistar.

- LHC Commissioning with Beam (LHC coordination, Latest news).

- No SL (Section Leaders) meetings last week. From the previous SLmeeting, it is worth mentioning that it has been decided to stabilize the fellow distribution to the present numbers. This means that ABP quota will stabilize to about 20 fellows/year corresponding to ~34% of the overall BE quota.

- Tatiana Pieloni was selected to join the ICE section (Vacancy number: BE-ABP-LIS-2010-48-LD) and she will start in the next weeks (exact date still under discussion).

- Executive summary Collimation Review July 2010: http://indico.cern.ch/getFile.py/access?resId=0&materialId=minutes&confId=100156:

- The work on adding dispersion-suppressor (DS) collimators and upgrading the IR3 collimation system during the 2012 shutdown must start now.

- A decision on an IR2 collimation upgrade during 2012 for ALICE will be taken later.

- R. Assmann as collimation project leader will set up a project structure for the 2012 collimation upgrade of IR3 and the associated work.

- LHC status report at LPCC (LHC performance and planning reports by the LHC weekly coordinators) => Ralph Assmann: http://indico.cern.ch/getFile.py/access?contribId=0&resId=1&materialId=slides&confId=101927.

- Record physics fill: intensities (19 h stable beam, only ~ 20% loss of intensity over 19 h, i.e. ~ 1% / h, which seems to be very good) and peak luminosity (~ 1.6E30 cm^-2s^-1 at the start of the fill).

- 3rd talk by WH at yesterday's LHCBCWG (Beam observation during collisions): https://lhc-commissioning.web.cern.ch/lhc-commissioning/meetings/20100727/LHC-BC-WG-Min27July10.pdf.

- Only 5 fills performed since the last meeting. Only one fill (#1232) with some observed losses, with the exact same pattern as usual, this time following the collapse of the separation bumps and the correction of the orbit against the reference orbit.

- Clear losses when trying to put the beams into collisions for ALICE, especially during that fill, with collisions very hard to find!

- Suspicious Schottky spectra in the log-book, to be understood what exactly is plotted, but potentials useful information => For those interested, please find a recent and very interesting presentation by Oliver Boine-F (GSi) on (longitudinal and transverse) Schottky spectra: Transverse Schottky signals and decoherence with space charge.

- Luminosity with and without transverse damper: some observed lifetime degradation, but, very small so not significant.

- Reminder on the LHC commissioning (short-term) plan:

- Discussion with W. Hofle on the request for the transverse damper for the transverse coupled-bunch instability in the LHC (he has to give a talk next Wednesday at the LMC): Could be interesting to have an estimate in the following cases (but it will not be for next week as a lot of work remain to be done on HEADTAIL to be able to implement the correct bunch pattern => Will be done in the next months by NM as part of his PHD thesis):

- 25 bunches (foreseen scenario for the end of the week and physics in August) => Exact pattern to be checked with WH.

- 43-bunch and 156-bunch schemes, 25 ns and 75 ns schemes at 450 GeV/c, 3.5 TeV/c and 7 TeV/c => The different filling schemes can be found at: http://cdsweb.cern.ch/record/691782/files/project-note-323.pdf.

- Note that the 50 ns scheme should also be looked at.

- Reminder: To the question "Above which number of bunches do we need the transverse damper to damp the transverse coupled-bunch instability?" the answer is the same as for the single-bunch instability. If there are no intrinsic nonlinearities (and linear coupling between the transverse planes), there will be an instability even after few bunches => We should already anticipate that after few tens of "consecutive" bunches the beam will be unstable and be ready to damp it. This subject will be studied in detail in the future by NM.

- SPS status week by week (from the coordinators): 2010.

- Of particular interest for the team is the fact that the magnet MBB.20750 had to be replaced last week and it has a coil displaced longitudinally on the right (clockwise) of 10/15 mm. Because of the displacement the RF contact of the pumping port 2074 could not be put in place.

3) EM simulations of the SPS pumping ports (Olav Berrig): ppt

- OB showed results for the case where the source and the test particles are in the centre, considering the case where there is no contact resistance and the case with a certain contact resistance (BS mentioned that it was suggested by CST to simulate a contact resistance by adding a piece of material with a certain resistance => Which one? Frequency-dependent? etc.). To be followed up as simulations of contact resistance are not easy. The recommendation in the past (with Fritz) was the following: SIMULATIONS should be performed for the slots etc. (i.e. geometric part) and MEASUREMENTS should be performed for the contact resistance.

- Bunch length = 20 mm. Is it the rms or full?

- The quadrupolar wakepotentials and dipolar wakepotentials can be found here => To be discussed at another meeting.

- Reminder on the (final) goal of the study: Try and explain the measurements performed in the SPS, in both longitudinal and transverse planes, before and after the impedance reduction campaign (i.e. shielding of the pumping ports).

- Next steps:

- Compute the RF power dissipated with and without shielding vs. bunch length.

- OB mentioned some technical problems (memory exception) => Suggestion by Rama to move to Windows 7 (with 64 bits) asap with more than 4 GB of RAM.

- The quadrupolar wakepotentials and dipolar wakepotentials can be found here => To be discussed at another meeting.

4) Actions to be taken for the next meeting

- No other actions than ones of 1st meeting.

5)  Miscellaneous

- Reminder on the beam-beam tools needed (in increasing order of complexity):

1) Possibility to make some tracking with SIXTRACK when betax* ≠ betay*, called flat beams. It is worth mentioning that 3 cases might be referred to as flat beams: betax* ≠ betay* (the case of interest here), epsx ≠ epsy and flat longitudinal distribution. In the case of betax* ≠ betay*, the output of MADX is fine (it is well computed) but the problem is then the data transfer between MADX and SIXTRACK => Not all the parameters (betas, sizes, intensities) are transferred. For the other two "flat" cases it should be fine.

2) 6D beam-beam lens (in fact it is 4D + time dependence) => We need this even if the strong beam is a single particle. There is a lens in SIXTRACK but it is not debugged. For instance it is not clear if the crossing angle is defined for the strong or the weak beam.

3) Effect of the 6D beam-beam lens on the strong beam => Both the divergence effect of the strong beam and crab tilt.

- EM discussed with Dieter Mohl the possibility to have a review of all the cooling techniques at some ICE section meetings. He would be pleased if we are interested. Many people seem to be => I will therefore contact him for a presentation in fall.

- The next (4th) meeting will take place on 04/08/2010 => Agenda:

1) PSB ring 4 instabilities (GR)

2) First results with very high single-bunch intensity in the SPS (BS)

- The meeting after (5th) will take place on 11/08/2010 => Agenda:

- Observations of fast beam losses in stable-beam operation in the LHC (Emanuele Laface)

- There will be not meetings on 18/08, 25/08, 29/09, 13/10 and 27/10.

Minutes by E. Metral, 28/07/2010.