Minutes of the ICE section
28th meeting on Wednesday 18/05/2011 (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), Xavier Buffat (XB).
Present/Excused: BS, CH, CZ, HD, EB, EHM, EM, EW, FS, GR, JLN, KL, MCAP, NB, NM, OB, TP, WH, XB, Alessandro Vivoli, Hannes Bartosik, Javier Cardona, Raymond Wasef, Roderik Bruce, Tom Mertens.
1) Newcomers / visitors
- None.
2) Comments on the minutes of the previous 27th meeting + Actions
- None.
3) General infos
- One comment: Where can we find the ATS note templates? => Reminder on the procedure for publishing at the Accelerator & Technology Sector (ATS) level: http://emetral.web.cern.ch/emetral/SomeUsefulLinks/ATS_Note_2010-031.pdf, where the guidelines and templates can be found at the end.
- SL meeting:
- EW has an invited talk at IPAC11 and she was accepted to go (BEMB).
- Military service for Swiss citizens: the contract will be put in hold for the duration of the military service and then resumed afterwards.
- CERN relay race: it will be held on 20/05.
- OliverB talked to SteveM and PaulC to re-institute a programme of Chinese visitors as it was the case in the 90ies with a stay between 3 months to a year. A potential candidate will be considered by GianluigiA.
- PaulC raises the point whether Japanese students could be offered to finish the experimental work at CERN to mitigate the effect of the earthquake earlier this year. The financial support will come from a central budget.
- LMC: in the analysis of the recent MDs it turned out that there are few closed orbit corrects with shorts.
- News on the LHC:
- Restarting after the 1st MD session + Technical Stop => We will increase the number of bunches injected to 108 and then 144 => Have a look to the LHC transverse instabilities (tomorrow).
- GianluigiA informed me yesterday night that they succeeded to inject batches of 108b with low losses and then also 144b => Ready to go to 1000+ bunches tomorrow.
- We had interesting impedance, HD and ecloud meetings and the 1st space charge meeting last Friday organized by FS.
- NM: single-bunch instability observations in the LHC at the beginning of the ramp during the collision tunes MD => Rise-times of ~ 1 s, which would be in good agreement with our predictions if the negative chromaticities were decreased to ~ -1. Was it (really) the case?
- Discussion with Sandra on the PS transition studies with HEADTAIL => Could be good to simulate the bunch length curve above transition during deceleration (starting from a matched point far from transition), to clearly see the bunch length step at transition and then to try and optimize the gamma jump (for a full validation of what she did).
- MDs in the SPS:
- It seemed that the nominal 25 ns beam could be accelerated with 2.7 to 2.9 micrometer transverse emittances with very small losses (<= ~ 3% for ~ 1.15E11 p/b. In the past the best I saw was ~ 5% for ~ 1.3E11 p/b => We are may be not that far...) => This would the first time after ~ 10 years to have such small emittances: in the past it was always ~ 3.5-3.6 in V, i.e. at the limit!!! Is it really true? => To be checked (as suggested by GianluigiA: gating of the wire scanner? etc.) => According to BS yesterday, it seems that indeed the gate was on the first bunch (for some cases at least) => To be followed-up and may be try and reproduce the plots done by GianluigiA in the past of transverse emittances evolution along the batch..
- 50 ns beam with 1.4E11 protons per bunch and 1.7 microm emittance.
- EB gave a talk at the LIU PS meeting held on 17/05/2011: working point optimization and space charge studies.
4) Review of Hamiltonian treatment of synchro-betatron motion: Part III/III (KL): pdf
- This is the last part of the review, where the synchro-betatron Hamiltonian is derived and discussed => Series of canonical transformations and RF fields.
- Canonical transformation to the kinetic energy, then canonical transformation to the reference orbit system. Then, expansions around the reference orbit system.
- The different terms can be clearly identified:
- Dispersion: linear synchro-betatron coupling,
- Chromaticity terms,
- Magnetic field terms.
=> Eliminate the 1st order synchro-betatron coupling by moving to the closed orbit system where all first order synchro-betatron terms cancel: this will naturally introduce the dispersion.
- Canonical transformation to the closed orbit system => Hamiltonian up to 3rd order in closed orbit coordinates.
- RF fields => Dynamic electric fields and averaging of the Hamiltonian.
=> The final decoupled synchro-betatron Hamiltonian (with the longitudinal and transverse parts separated).
- The longitudinal Hamiltonina given by GR is his USPAS09's course is recovered, which was one of the main goals of this analysis! The next step could be to study the synchro-betatron resonances.
5) Review of IBS: analytic and simulation studies (Alessandro Vivoli): ppt
- Motivation => Studies for the CLIC damping ring, where the 3 main effects are: radiation damping, quantum excitation and IBS.
- IBS is the effect due to multiple Coulomb scattering between charged particles in the beam.
- Conventional theories of IBS: Growth rates are calculated at different points of the lattice and then averaged over the ring. Conventional calculation of IBS effect in Accelerator Physics derive an estimation of the IBS growth times from the theories of Bjorken-Mtingwa or Piwinski.
- Alessandro reviewed in some detail the theory from Bjorken-Mtingwa, starting from a bunch distribution and some arguments of relativistic quantum mechanics. The invariant Coulomb scattering amplitude is derived from the Mott cross section in the non-relativistic limit and small-angle scattering approximation. The motion of the particles in the ring can be expressed through 3 invariants (and 3 phases). The growth times due to IBS can be estimated after having defined the rms emittances and using Gaussian distributions to reduce all the integrals to Gaussian integrals. The Coulomb logarithm is not a well defined quantity. It comes from the integration over the scattering angle. There is not complete agreement to define it.
- Alessandro wrote a code called SIRE = Software for IBS and Radiation Effects => Goals: (1) Follow the evolution of the particle distribution in the DR (we are not sure it remains Gaussian) and (2) Calculate IBS effect for any particle distribution (in case it doesnt remain Gaussian).
- SIRE has been benchmarked against theories in case of Gaussian distributions for the CLIC DR and for the LHC, which revealed a good agreement.
- The evolution of the particle distribution shows deviations from Gaussian behaviour due to IBS effect.
- On page 27 we expect the IBS gives thicker tails than Gaussian and they found the opposite with the SIRE code... => To be followed up.
- Comment from Roderik: V. Lebedev said that when he took points every ~ 10 cm the results were "better" but then there is a trade-off between time and precision...
- Alessandro gave many references for the Bjorken-Mtingwa and Piwinski theories. Roderik and Tom mentioned that there is also the following recent one: "Analytical Approach to Eigen-Emittance in Storage Rings, Boaz Nash , SLAC-Report-820" (http://www.slac.stanford.edu/cgi-wrap/getdoc/slac-r-820.pdf).
6) Actions to be taken for the next meeting
- Old actions.
- No new actions.
7) Miscellaneous
- The next (29th) meeting will take place on 25/05/2011 => Agenda:
1) 1st LHC beam-beam observations in 2011 (TP)
- See preliminary agendas for the next meetings.
Minutes by E. Metral, 05/06/2011.