Minutes of the ICE section
25th meeting on Wednesday 20/04/2011 (08:40-10:30, 6/2-004)
ICE members: Benoit Salvant (BS), Christian Hansen (CH), Carlo Zannini (CZ), 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), Tatiana Pieloni (TP), Werner Herr (WH).
Present/Excused: BS, CH, CZ, HD, EB, EHM, EM, EW, FS, GR, JLN, KL, MCAP, NB, NM, OB, TP, WH, Alessandro Vivoli, Fritz Caspers, Hannes Bartosik, John Jowett, Rama Calaga, Riccardo De Maria, Vittorio Vaccaro..
1) Newcomers / visitors
- None.
2) Comments on the minutes of the previous 24th meeting + Actions
- No comment (the minutes of the last meeting were not yet released).
3) General infos
- OB had a comment about updates to CST => Discussions with John Evans and Lev Mozhaev.
- SL meeting:
- Fellows: Requests to be sent to OliverB by 25/4 with copy to DelphineR => There is no request from ICE for this committee.
- Renovation of the offices: work will start in building 9 from the first week of June and it will take approximately 6 weeks per floor. DelphineR will inform the people involved by e-mail.
- Proposed dates for the next ABP Group Meeting are the weeks of: May 23, June 14 (the Tuesday or the Wednesday), June 20 (will be finally avoided) or June 27 (which is the current preference).
- The proposed modification of the ATLAS vacuum pipe has been approved at the last LMC.
- HL-LHC kick-off Internal Meeting took place as foreseen last Friday 15/04/2011: http://indico.cern.ch/conferenceDisplay.py?confId=132315.
- News on the LHC:
- New luminosity record => ~ 3.8E32!, i.e. very close to the Tevatron record (~ 4.02E32).
- Some measurements just after the 2011 LHC scrubbing run:
- Summary of the heat load measurements with the corresponding filling schemes as analyzed by Walter Venturini Delsolaro. Laurent and Walter are checking the analysis. What is a bit strange is the systematic higher load in two cells. What is the heat load that we would expect for the synch light?
- Did we take some data during the night when we went in collision for the second time with 2 trains of 228 bunches? During last week-end (16-17/04/2011) it was tried to go in collision with trains of 72 bunches and when we went in collision we lost quite some beam and get a beam dump. It would be interesting to see what has been logged and understand what is happening in such a case.
- We should try and look at the emittances through the ramps that we had on 16/04/11 as it seems that we had some electron cloud activity in the arcs => Do we see some transverse emittance blow-up?
- Some analysis by Christian Hansen: http://chansen.web.cern.ch/chansen/EURONU/BSRT/bsrtScrubbApril11.html#april16.
- We should have a look to the loss patterns observed on Saturday 16/04/11 when we went in collision (ELogbook entry at 14:59) => Seems to indicate some beam-beam effects. Is it linked to large transverse emittance bunches (due to ecloud?)? To be followed up.
- WH mentioned that if the spread of transverse emittances is too large then beam-beam could be the killer for the large-emittance bunches (already observed in the past with other machines) => Explanation from WH: the large-emittance bunches feel more the nonlinear part of the beam-beam force from the smaller-emittance bunches.
- One should aim for ~ 10-20% transverse emittance spread.
- GianluigiA discovered that the PSB ring 4 had larger transverse emittances and this was the 2nd batch of 12 bunches in the LHC. Reminder in the sequence of PSB rings sent to the PS: 3-4-2-1 ("On a besoin de 3 des pour jouer au 421...).
- Preparation of the 1st LHC MD block (week 18) => Beam-beam and TCBI. CH might be interested to join the BI team (Federico Rocarolo) to compare the different transverse emittance measurements (WS, BGI, BSRT).
- PS BWS in SS68:
- Discussion (and visit) with BS, EM and some BI colleagues (William and Gerard) on Monday 18/04/11. The idea is that William prepares his tank (with the possibility to have the wire IN or not, and the ferrite IN or not) on Monday 02/05 and we could do wire measurements the rest of the week (under William's supervision in case we want to play with the BWS wire, not to break the BWS wires) => From Tuesday 03/05 to Friday 06/05. We should try and be prepared. Hugo is also willing to make some measurements to see the effect of the ferrite (as an impedance reduction technique) and Olav would also love to perform these measurements. EM will also try and join.
- News from the PSB ring 1 instability mentioned last week by GR => It seems it disappeared.
- Interesting results presented by SandraA at the last HDWG meeting => HEADTAIL simulation during the accelerating ramp in the PS. Some nodes seem to appear during acceleration which were not present in static => To be followed up.
4) Current impedance activities (BS): pptx
- Many requests these days, so we need to clearly assign priorities and responsibilities (done).
- Since this meeting, more discussions took place:
- For the TDI (which is for the moment the only equipment whose impedance could be ~ 2-3 times higher than predicted) => HD.
- LHC RF cavities and septa => Indian collaboration (still under discussion).
5) News from the US of the 6D beam-beam lens (FS): ppt + Beam-beam note
- Goal of the BNL-FERMILAB-CERN Collaboration:
- Benchmaking of the 3 codes: Lifetrac (with A. Valishev), SixTrack (with FS) and SimTrack (with Y. Luo). Idea from Wolfram Fischer (weak-strong mainly).
- DA and Tune foot-prints in view of BB.
- 1st code = Lifetrac (FERMILAB):
- Weak-strong BB code (e-p colliders 1995)
- Non-equilibrium distributions (2003-2004) => conventional macro particle tracking code
- Machine lattice 6D map + thin multipoles. Not a very good model of the chromaticity which has to be introduced in an artificial way.
- Beta-functions from MAD-X TWISS
- Thin multipoles from MAD-X
- RF sinusoidal kick
- First and second order chromaticity via additional deltap phase advance and chromatic drifts before and after IP
- 6D Hirata of sliced head-on, parasitic are thin
- Introduction of noise once per kick
- 10000 particles 1e6-1e7 turns => better beam emittance and lifetime:
- Averaging density distribution over simulation step (10000 turns)
- Weighted distribution with more particles in the tails
- MPI with non-interacting nodes
- Issues:
- How well can the lattice approximation work compared to the real thing?
- No tune foot-print available (work in progress)
- 2nd code = SixTrack (CERN):
- Traditional single particle element-by element code
- Expanded (and not Extended! Typo in the slides) Hamiltonian (bad for extremely large deltap). Expansion up to 2nd order.
- Symplectic treatment of thin and thick (second order) elements => full Ripken theory
- 6D extended Hirata BB formalism (Ripken)
- Full differential algebra and NormalForm implementation a pre-PTC approach
- Optimized for speed
- Elaborate run environment for massive tracking runs
- Issues:
- The thick lens part is presently not fully operational but can be easily replaced by going to thin mode
- No plans for emittance growth nor lifetime
- 3rd code = SimTrack (BNL):
- C++ library
- 4th order symplectic integrator
- 4d and 6d BB
- Benchmark Tracy II and BBSIM
- Many elements
- Parameter change on the fly
- RHIC Au run and BB head-on compensation
- Particle loss
- emittance growth & lifetime
- Linked to Mathematica: SVD, polynominal fitting etc.
- Issues:
- Thinlens lattice not fully readable
- No BB crossing angle implemented
- WH said that the formula for the reduction of the BB tune spread by the crossing angle was first derived by Augustin (from the PS) few decades ago.
- There is a very good agreement for the HO tune footprint between 4D and 6D for deltap = 0.
- It was mentioned that we have to compute the tune footprints for all the different deltap and superimpose them.
- Many discussions during the meeting about the BB tune footprints and in particular the effect of the longitudinal bunch profile (static vs. dynamic, etc.) => Will be discussed in detail in the space charge working group. Action1: FS to review in detail the SC and BB (HO) tune footprints.
- Questions from RiccardoDM linked to the HL-LHC studies => Still to be discussed in detail.
6) Review of IBS: analytic and simulation studies (Alessandro Vivoli) => POSTPONED
7) Actions to be taken for the next meeting
- Old actions.
- New actions:
- Action 1 (FS): Review in detail the SC and BB (HO) tune footprints.
8) Miscellaneous
- I will not be at CERN next week.
- The next (26th) meeting will take place on 04/05/2011 => Agenda:
1) Measurement opportunities with the LHC transverse damper (Daniel Valuch and Wolfgang Hofle),
2) Simulations tools for the time evolution of the heavy ions beam parameters (Roderik Bruce),
3) Comparison between simulations and measurements in the LHC with heavy ions (Tom Mertens).
- See preliminary agendas for the next meetings.
Minutes by E. Metral, 29/04/2011.