Minutes of the ICE section
50th meeting on Wednesday 14/03/2012 (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), Elias Metral (EM), Elena Wildner (EW), Frank Schmidt (FS), Giovanni Iadarola (GI), Giovanni Rumolo (GR), Jean-Luc Nougaret (JLN), Kevin Shing Bruce Li (KL), Nicolo Biancacci (NB), Nicolas Mounet (NM), Olav Ejner Berrig (OB), Serena Persichelli (SP), Tatiana Pieloni (TP), Werner Herr (WH), Xavier Buffat (XB).
Present/Excused: BS, CH, CZ, HD, EB, EM, EW, FS, GI, GR, JLN, KL, NB, NM, OB, SP, TP, WH, XB, Alexander Molodozhentsev (from KEK), Christian Carli, Fritz Caspers, John Jowett, Miriam Fiterrer, Sandra Aumon, Mauro Migliorati, Michaela Schaumann, Simone Gilardoni.
1) Newcomers / visitors
- None.
2) Comments on the minutes of the previous 48th and 49th meeting + Actions
- Minutes still to be released.
3) General infos
- No particular comment from anyone.
- MARS => Will/should be finalized next week.
- SL meeting(s):
- Nothing special.
- CERN will hold open days in 2013 and the Director-General will appoint a coordinator.
- News from LHC:
- 1st beam of 2012 should be injected this evening!
- LBOC talk yesterday by EM on recommended values of chromaticities, octupoles' currents and bunch length => http://emetral.web.cern.ch/emetral/ICEsection/2012/2012-03-14/LBOC_EM_13-03-12.pdf:
- An important point to clarify is to understand why we needed ~ 200 A at top energy last year, which should translate to ~ 450 A this year (with the tight collimators' settings increasing the complex tune shift by ~ 2.3) => Important MD to be done.
- TCTP:
- Update of the TCTP heating estimates (HD).
=> Green light given by the impedance team.
- Action 1 (impedance team): Send a sample of the TT2-111R selected ferrite to vacuum people (Vincent Baglin) to measure the outgassing properties of the ferrite as a function of temperature.
- TDI:
- New design for the spare approved by RF team => See in particular http://emetral.web.cern.ch/emetral/ICEsection/2012/2012-03-14/ModificationsForSpareTDI_2012_EM.pdf and minutes of a meeting organized yesterday by Marc Timmins.
- It is worth noticing that a bake-out of 300 deg C would lead to a deformation of ~ 4 cm, which is very close to the measured value => See page 4 of https://edms.cern.ch/file/1204797/1/Results_Analysis_reinforced_TDI_Beam_screen.pdf.
- LRFF (http://emetral.web.cern.ch/emetral/LRFF/LRFF.htm) => 1st kick-off meeting next Tuesday.
- HL-LHC Task 2.4 (https://espace.cern.ch/HiLumi/WP2/task4/SitePages/Home.aspx) => Everything (collaboration etc.) is in place and we can start working...
- IEFC workshop last week => Anything important for ICE?
- Talk by BrennanG on future projects mentioning the need to have 2 new extraction kickers => To be followed up in particular by impedance team.
- Beam-beam:
- Informal meeting organized by EM etc. to review the need (or not) of an improve 6D beam-beam lens => Minutes to come (EM).
- HL-LHC => What can we do? What do we plan to do?
- A general review of the requirements in terms of computing needs for impedance calculations and for space charge is required => Followed up by FS.
4) LEIR issues (Christian Carli): pptx
- CC discussed the motivation for LEIR, LEIR after complete installation, LEIR Layout, LEIR Cycles, LEIR Lattice, injection with stacking all three phase spaces, accumulation, dynamic vacuum, impedances and instabilities, LEIR run 2011, and finally ideas and plans for the future.
- 2 proposals in the past to increase the brightness for LHC: laser ions source or accumulation in synchrotron with ecooling. The second one (accumulation) was finally chosen.
- Construction of LEIR reusing most of the LEAR HW + inclined septum and new ecooler from BINP.
- Very complicated multiturn injection with stacking in all 3 phase spaces over 70 turns. Simulations were done and predicted an efficiency close to 60%. D ~ 10 m required at injection for multi-turn injection.
- Ecooler is used at injection energy (with fast cooling times of the order of 200-400 ms) but could be used at an intermediate energy => Could be used in case of blow-up at the beginning of the ramp?
- Ecooler induces coupling, which is compensated by solenoids etc.
- LEIR layout: ~ 2-fold symmetry, perturbed in fact by the ecooler.
- Somewhat irregular lattice (not at all a FODO structure!) as many small machines.
- C-shape magnet and not insulated vacuum chamber => ramp induces net current along the chamber and quadrupolar components. Past comment from Michel Chanel: it would be difficult to have a fully "bakable" machine (as it is the case with LEIR at the moment) with an isolated vacuum chamber => Maybe to be re-discussed.
- The advantage of having a slower injection bump decrease (thanks to the inclined septum) is that we can then inject more pulses.
- The accumulation is performed with a coasting beam (i.e. RF OFF) => Schottky spectrum is the main diagnostic tool (the accumulation is made at a lower, optimized, momentum).
- Dynamic vacuum and lifetime:
- POP measurements in 1997.
- Upgrades made:
- Ions lost at the end of bending magnets => Absorbers with Au coating installed their to reduce the outgassing.
- NEG coating in straight sections to improve the vacuum there.
- Space charge, impedances and instabilities:
- Direct space charge tune shift should be a bit less than 0.1.
- If the transverse damper is swtched off the beam is unstable => We could make a test and measure the rise-time.
- The 2nd means to stabilize the beam is to modulate the ecooler gun voltage to shake the beam and increase the momentum spread (note that it was not required during the last run).
- LEIR run in 2011:
- Excellent injection efficiency of > 50%. Why was it much better than year before?
- 7 injections.
- Loss at capture and start of the ramp => Seen since several years and strongly depends on working point (and also maybe chromaticity etc.). But the extracted emittances are within specs. So the problem is only a beam loss problem (even if could be linked to emittance growth if the initial emittances were really very small...).
- IBS growth rates (question from JohnJ): Some estimates made in the past => Could maybe try to review them.
- Current hypothesis: Space charge limit lower than expected for a machine with irregular (not at all FODO) lattice? or working point too close to resonances? => To be studied in detail. Maybe we could use the cooling at an intermediate energy, after the start of the ramp done with larger transverse emittances and therefore smaller space charge?
- Optimum tunes now (nominal one): 1.82 / 2.72.
- Comment from SashaM: The super-periodicity of this machine is 1 meaning that all resonances could be systematic.
- There are no resonance corrections for the moment but there are elements installed for this purpose.
- SashaM asked for some MADX file => See optics repository and/or discuss with OB: http://cern-accelerators-optics.web.cern.ch/cern-accelerators-optics/.
- Reminder from CC: We keep Bdot/B constant at the beginning of the ramp.
- Ideas and plans:
- Run 2012.
- Understanding of the loss at the beginning of the ramp:
- The transverse emittances could be very small according to BIPMs => To be followed up.
- We could try to have larger emittances (using a not optimized cooler) => Could be important to check space charge effects at start of the ramp.
- Impact of Bdot etc.
- Impedance model and understanding of instability limits, better understanding of ecooling etc.
=> Could be a nice subject for someone: Intensity limitations in LEIR => Both theoretical / simulation studies and machine studies. Could be also coupled to studies for the ELENA machine.
- Biomedical facility:
- First discussed at the Physics for Health in Europe Workshop at CERN in February 2010.
- LEIR well suited for such an installation => studies on requirements started recently.
5) Actions to be taken for the next meeting
- Old actions.
- New action:
- Action 1 (impedance team): Send a sample of the TT2-111R selected ferrite for the new TCTP to vacuum people (Vincent Baglin) to measure the outgassing properties of the ferrite as a function of temperature.
6) Miscellaneous
- The next (51th) meeting will take place on 21/03/2012 => Agenda:
1) Past collective effects studies for DAFNE and possible contributions to the CERN PS impedance model (Mauro Migliorati from Roma, La Sapienza),
2) Beam impedance measurements (OB).
- See preliminary agendas for the next meetings.
Minutes by E. Metral, 14/03/2012.