Minutes of the ICE section
42th meeting on Wednesday 19/10/2011 (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), 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), 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, TP, WH, XB, Alexey Burov, Elena Shaposhnikova, Fritz Caspers, Georges Trad, Hannes Bartosik, Miriam Fiterrer, Theodoros Argyropoulos.
1) Newcomers / visitors
- None.
2) Comments on the minutes of the previous 41st meeting + Actions
- None.
3) General infos
- SL meeting:
- Nothing special to report.
- News on the LHC:
- Very good last week with many records.
- ATLAS&CMS > 5.1 fb^-1 with peak lumi at ~ 3.6E33.
- Running now with Nb slightly above 1.4E11 p/b and not so many problems until now. Note that it was after the 25 ns MD of last Friday.
- 25 ns MD last Friday => Up to 1092 bunches could be accumulated at injection (with large chroma ~ 15, still large transverse emittance blow-up, important cryo heat lead etc.). Promising (no major showstoppers, just more time needed to scrub) => To be continued (discussions ongoing for end of this week...)
- TDI => Important reduction of vacuum pressure opening it from +- 20 mm to +- 50 mm. Note also that the bunches were longer than before by ~ 50 to 70 ps => See Picture TDI.
- Instability observed on Monday 17/10/11 with ~ 1.45E11 p/b (see some Slides finished after the meeting):
- Picture 1. Current interpretation (still to be confirmed): Loss of Landau damping for TCBI mode 1 (as mentioned already at some LBOC meeting: https://lhc-beam-operation-committee.web.cern.ch/lhc-beam-operation-committee/minutes/Meeting17-30_08_2011/RecentObservationsOfLHCBeamInstabilities.pdf).
- Seems consistent with updated plot by NM: Picture 2 for a transverse emittance of 2.5 microm (still stable) and Picture 3 for 2.2 microm (at the limit of stability).
=> Recommendations: Increase a little bit the octupole strength, to go from a current of - 150 A to - 200 or - 250 A to have some margin. We should also always try to reduce the chromaticity as much as possible.
- TDI MD during the next MD block => EM will not be around. Who could follow this MD and measure at injection the tune shift vs. gap? => To be followed up by the impedance team.
- PTC 1/2 day review => Converging to 09/11/11 (from 08:30 to ~ 13:00). The whole group will be invited soon.
- CNGS neutrinos follow-up... => Paper from Van Elburg: Time of flight between a Source and a Detector observed from a Satellite.
- TCTP recommendations sent by BS after a huge simulation campaign => Many thanks to BS and all collaborators!
- Question from ElenaS: What is the current LHC longitudinal impedance model => Action1 (Impedance team).
4) Can circular optics be useful for upgrades of the LHC complex (Alexey Burov): pdf
- Contents:
- 1. Symplectic algebra and eigenvectors (Lebedev & Bogacz, IOP 2010);
- 2. Emittances and sigma-matrices (ibid);
- 3. Circular modes and beam adapters (Burov, Derbenev, Nagaitsev, Phys. Rev. E, 2002);
- 4. Perturbation theory (Burov, Phys. Rev. ST-AB, 2006);
- 5. Coherent motion (Burov & Lebedev, Phys. Rev. ST-AB, 2007);
- 6. Space charge suppression (Burov & Derbenev, FERMILAB-PUB-09-392-AD).
- Equations of motion for linear Hamiltonian => Can be found for instance in Lebedev&Bogacz' paper.
- Coupling could come from both skew quads and/or solenoids.
- 10 independent parameters for 16 matrix elements.
- Det = 1 only works as Det = - 1 is not possible.
- Page 7 => There is a font problem with a xi appearing... It should be real part. Also, font issue for the transformation from x to xi...
- Reminder: there are 2 parametrizations of eigenvectors:
- Mais-Ripken => Only 8 independent parameters. Comment from FS: this can be extended to the 6D case, which is done for instance in PTC.
- Edwards-Teng.
- The uncoupled modes are planar modes. If we excite a mode in a direction it will oscillates (only) in the same direction.
- From the eigenvectors we can know the transfer matrix.
- Circular modes => If we excite only 1 mode then we would see at a certain position that the beam makes a circle (in the x-y plane) => 2 circular modes: clockwise and anti-clockwise (describing the motion in the x-y plane).
- We could have in the same machine a portion with planar modes and one with circular modes and we can go from one to the other without emittance blow-up as in both cases we have an Hamiltonian system (conserving the emittance).
- To create circular modes we need to create a rotationally invariant angular matrix.
- Beam adapters => Example to transform 2 circular modes in 2 planar modes titled by 45 deg, requiring only 3 skew quads.
- To be finished next week, with in particular possible interesting applications for the upgrade of the LHC injectors and LHC itself.
5) Actions to be taken for the next meeting
- Old actions.
- New action:
- Action1: Impedance team to give the current LHC longitudinal impedance model.
6) Miscellaneous
- The next (43th) meeting will take place on 26/10/2011 => Agenda:
1) End of AlexeyB's talk on circular modes => Possible interesting applications.
2) Anomalous Diffusion for Phase Space Density Modification (Alexey Burov).
- See preliminary agendas for the next meetings.
Minutes by E. Metral, 19/10/2011.
