Minutes of the ICE section
22th meeting on Wednesday 30/03/2011 (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, Chandrashekhara Bhat (Fermilab), Eirini Koukovini Platia, Frank Zimmermann, Hannes Bartosik, Javier Cardona, John Jowett, Octavio Dominguez Sanchez de la Blanca, Vittorio Vaccaro (Naples).
1) Newcomers / visitors
- None.
2) Comments on the minutes of the 21th meeting + Actions
- EM will have to remove Thys Risselada from the list of people receiving the emails for meetings/minutes and add Tom Mertens.
- 1 comment from GR about BS's simulations for SPS BPMs linked to Action 33 => It seems BS and GR already discussed this 1-2 years ago and that it is already understood => To be followed up and concluded in the impedance working group.
3) General infos
- No particular comment from anyone.
- No SL meeting last week due to IEFC workshop.
- News on the LHC:
- Readiness to go to 296 bunches. Up to now we accelerated 200 bunches.
- 1.38 TeV run done as foreseen (34 h requested and obtained):
- Some losses were observed in collision: The Blue beam seemed to suffer much more than the red one. Why? Is it really beam-beam? Chromaticity?
- Octupoles were used to stabilize the beam when the ADT was OFF to change from the injection tunes to the collision tunes (as there were no functions ready for all that at this energy) => Before going into collision they put OFF the ADT, the beam was going unstable so they put octupoles (40 A i.e. the same strength as we have with 100 A at 3.5 TeV) and the beam was stable again.
- Next: Ready for 296 bunches at 3.5 TeV when we return for physics after the LHC scrubbing run. Tevatron record luminosity is in reach ( ~ 4E32).
- WH and beam-beam team did a luminosity leveling test in IP8 by changing the beam separation up to 2.5 sigmas => Very successful as no beam lifetime degradation was observed.
- Hugo Day will attend the next CSTs European User Group Meeting which will be held in the Marriott Munich Airport hotel on 17-19 May 2011 (after the green light from Delphine and Oliver). Note that he doesn't need to pay for the registration fees of 220 euros (thanks BenoitS who arranged this with Monika Balk!) as he is a student who will give a talk.
- IEFC workshop last week.
- Preparation of the LHC scrubbing run => See yesterday's talk by GianluigiA. See discussion below.
- Discussions ongoing to have a talk on Sussix as foreseen => 13/04/11 (ongoing).
- TSC deadline 14 April 2011. The forthcoming TSC will take place on Tuesday, 26 April 2011. As usual, access to e-RT will be granted on request, so please send Catherine Rossat <catherine.rossat@cern.ch> an email if you need access to the Technical, Doctoral and Administrative Students folder. This tool will only be used for the consultation of the forms and associated documents, so please return her your requests by E-MAIL via Oliver Bruning and myself. Your request should include the name of the student selected and one or two reserve candidates, the priority of the project proposed to candidate, the group/section with name of supervisor, a short job description (= 5 lines) and the budget code.
- EM reported some recent results from NM about the multi-bunch HEADTAIL code => NM compared the results from the new code for the case of the SPS at injection with equipopulated equispaced bunches (924) to the theoretical predictions from Sacherer and Laclare (in the case of a dipolar impedance only, and varying the chromaticity) and found a good agreement (to be discussed in detail at some point), which gives good confidence that the code is working well. Many other cases are planned to be studied in detail in the near future (SB and CB mode coupling with Laclare formalism using different distributions etc.) => See a comparison made in the past for the SB mode coupling at SPS injection between HEADTAIL, MOSES and Laclare (using a water-bag bunch): http://ab-dep-abp.web.cern.ch/ab-dep-abp/LIS/Minutes/2007/20071015/salvant.pdf => Would be good to check that using the same distribution for Laclare as the one in HEADTAIL (truncated Gaussian) we obtain an even better (perfect?) agreement. Then we could extend it to the multi-bunch case and compare with HEADTAIL...
4) Review of Hamiltonian treatment of synchro-betatron motion: Part I (KL): pdf
- KL discussed the first part as foreseen (Motivation and Model Introduction). The 2nd part (The Transverse Hamiltonian) and the 3rd part (The Synchro-Betatron Hamiltonian) will be discussed next week.
- KL clearly explained his motivations and the goal => Attempt to gather different resources to summarize the known theory in a more or less complete and comprehensible manner => Derive the Hamiltonians found for instance in GR's USPAS2009 course or WH's talks on "Numerical and Computational Tools in Accelerator Physics: An introduction" (8 parts): http://zwe.web.cern.ch/zwe/METHODS/.
- 1st we have to create our universe => Only 3 objects are needed: 2 (parameter and configuration) manifolds (a manifold is a topological space that on a small enough scale resembles the Euclidean space of a specific dimension, called the dimension of the manifold => a line and a circle are one-dimensional manifolds, a plane and sphere (the surface of a ball) are two-dimensional manifolds etc.) and 1 map (to connect them). The parameter manifold = our world (= Minkowski space => the 3 ordinary dimensions of space are combined with a single dimension of time to form a 4-dimensional manifold for representing a spacetime) and the configuration manifold = some quantity we are interested in.
- Then 3 other objects can be derived: the world bubble, the phase space and the Jacobian => All physics is in finding the map.
- Definition of the action S = the volume of the world bubble and it can also be expressed with the Lagrangian (involving the determinant of a function of the Jacobian).
- Then we apply "basic physics" => The principle of least action: dS = 0 (the action has to be stationary).
- Then, as we want in accelerator physics to treat point particles and not fields, we introduce the classical limit (we neglect quantuum effects here) => The action S becomes the length of the world-line.
- Then, we introduce the electromagnetic theory via the U(1)-gauge coupling by moving from the standard to the covariant derivative. Amu is the 4-potential for the electromagnetic force. Note that mu = 0, 1, 2, 3 (0 for time and the other three for space coordinates). => The action S becomes the covariant length of the world-line.
- Electromagnetic Hamiltonian = Legendre transform of the electromagnetic Lagrangian. Be careful in the notations => q is either the charge (in front of the potential A) or a space coordinate. Furthermore, it seems there are some typos and that H should be defined with the opposite sign in page 22, with qdot instead of q, and that in page 23 the small p should be replaced by a capital P => KL corrected these typos and updated his version.
- Applying the least action principle (expressing the action S with respect to the Hamiltonian) leads to the Hamilton equations of motion. It is better to use the Hamiltonian instead of the Lagrangien as it then leads to "more symmetrical" equations of motion.
- KL then discussed the symplectic structure (Reminder on the symplecticity condition for a matrix M => MT S M = S with S a special matrix which verifies in particular that det S = 1, which means that there is a conservation of the phase space area) and the Hamiltonian vector field using the Lie operator (:H:) => The Hamiltonian is the generator for translations in time for any distribution function => We recover the known results: the only thing we need to know is the Hamiltonian and we can then deduce the evolution in time of any distribution function.
- The Liouville's theorem (which states that the local particle density does not vary with time when following the motion in canonical variables) was then finally discussed => Preservation of the volume form.
- Reminder (after Vittorio's comment): a conformal map is a function which preserves the angles => This method is used for instance to compute the impedance of elliptical pipes etc.
5) Preparation of the LHC scrubbing run: exact dates + measurements to be done (based on last year experience) + people (EM): ppt
- EM discussed briefly the LHC scrubbing run => See talk from GianluigiA at yesterdays LBOC (https://lhc-beam-operation-committee.web.cern.ch/lhc-beam-operation-committee/) for a detailed description of the 2011 LHC scrubbing run.
- Should start this Saturday, but it might be delayed by few days => More news on Friday.
- Special benchmarking experiment we want to do at the beginning and at the end to both quantify the scrubbing and constrain our simulation parameters => Inject several times 2 batches of 36 bunches (spaced by 50 ns) with different gaps instead of doing many injections as done last year to speed up the process.
- Other measurements which should be made/followed up and ICE people involvement:
1) Vacuum pressures => Vacuum team (MiguelJ, VincentB) + OctavioD.
2) Heat load => Cryogenics team (LaurentT, SergeC) + Humberto Maury Cuna? (tbc).
3) Emittance along the trains => FedericoR? + ChristianH.
4) Lifetime of the bunches along the trains => GiuliaP? + KL.
5) Tune shift along the trains with Schottky => TatianaP? (tbc).
6) RF stable phase => ElenaS? + Chandra.
7) Intrabunch and coupled-bunch motion with Headtail monitor => BS and HannesB.
8) Coupled bunch motion with transverse dampers => RiccardoDM? + VerenaK? + BS.
9) LHC BPM => NM? (tbc) + Eirini.
6) 1st LHC beam-beam observations in 2011 (TP) => POSTPONED TO THE NEXT MEETING
7) Discussion about IPAC2011 papers from ICE & colleagues
- We reviewed briefly the different subjects which could be presented => Reminder of the deadline: All the ICE members (who want to present a paper and have someone to present the results there) should send the abstracts to Oliver Bruning and myself on Monday 4 April 2011 at the latest (the deadline for abstract submission is 13 April 2011, but the abstract must firstly be approved by our group leader (+ project leader if necessary) and then one should send it to Anna Mackney by Thursday 7 April for approval by the Department Head ).
8) Actions to be taken for the next meeting
- Old actions.
9) Miscellaneous
- The next (23th) meeting will take place on 06/04/2011 => Agenda:
1) 1st LHC beam-beam observations in 2011 (TP)
2) Review of Hamiltonian treatment of synchro-betatron motion: Part II (KL)
- See preliminary agendas for the next meetings.
Minutes by E. Metral, 30/03/2011.