Minutes of the LIS Section meeting held on 15th November 2010

Present: G. Arduini, H. Bartosik, C. Carli, S. Gilardoni, J. Gil Flores, M. Juchno, G. Prior

General Information (Gianluigi) 

Gianluigi reminded the deadline for the submission of the request for Technical and Doctoral Students

LIU (LHC Injector Upgrade): The project structure has been finalized: 3 coordinators have been nominated: S. Gilardoni for PS, K. Hanke for PSB and B. Goddard for SPS.

LHC: Since the last meeting. A total integrated luminosity close to 50 pb-1 has been delivered and a peak luminosity above 2x1032 cm-2s-1 has been achieved. Tests have been performed with a 50 ns beam. Important pressure rises due to electron cloud have been observed. A series of studies have been conducted in order to constrain simulations and provide input for the operational scenario for next year. Switch to ions went smoothly and an integrated luminosity of more than 2 ub-1 has been delivered (the target was set to 1 to 5 ub-1). 

Christian noted that some optimization is still required in the filling scheme for ions. For the moment we are injecting trains of 4 bunches but injection of 8 trains of 8 bunches should be tested in the SPS and could help in reducing the amount of time spent in the LHC at injection in view of minimizing emittance blow-up and losses.

Jamie Gil Flores has joined ABP/LIS as technical student with Simone. He will work on the assessment of the performance and specifications for the PS BLMs.

PS Main Magnet Model (M. Juchno) - slides

2D magnetic field calculations have been performed and the effect of the different circuits has been simulated for different values of the main coil current. Each multipole of the magnetic field resulting form the numerical simulations  has been decomposed as a linear combination of of the current of each circuit (transfer matrix model) but this approximation is not satisfactory. A better approximation of the magnetic field simulations is obtained by replacing the linear coefficients with coefficients which are functions of the main coil current (non-linear transfer matrix model). A comparison between the non-linear transfer matrix model and measured data collected in 1992 for two dedicated cycles shows discrepancies which are particularly important for the cycle going to higher current. Larger discrepancies are observed for teh focussing half-unit. The difference could be related to the different separation among the blocks composing the two half units. The measurements taken in 1992 were performed after pre-cycling the magnets to provide the same magnetic history. The present model does not include the effect of remanent fields and magnetic history. This could lead to errors in the order of a few Gauss as evidenced by an experiment in which the currents required to obtain a magnetic field corresponding to 14 GeV/c for different magnetic histories (different supercycles) have been compared. Although the magnetic model is not sufficiently accurate to determine the multipoles in absolute terms (i.e. determine the multipoles corresponding to a given set of currents) it can reproduce pretty well the variation of tune for a given variation of the current around a given working point.

Mariusz concluded providing a preliminary plan of the remaining activity. 

Round Table (all)

Simone

Simone is working on the comparison of different types BLMs in the PS. Cherenkov detectors (form PEP2) have been compared with ACEM (presently installed in the PS) and LHC ionization chamber of smaller volume. The preliminary analysis shows that LHC type ionization chambers are not fast enough for turn-by-turn measurements. PEP type detectors are fast enough (even faster than the   Fastest signal. Even faster than ACEM but the signals show some features not yet totally understood. LHC SEMs have been installed as well but their sensitivity is too low.

Gianluigi asked whether diamond detectors could be an option but probably their size is too small and geometrical effects in the beam loss reconstruction become very important.

The issue with INCA observed last week has been fixed (GFA functions could not be trimmed any more) last Thursday, but there are still issues for the cycle generation which is not user-friendly at all.

MTE: a supercycle with no AD cycle but no effect has been observed on losses/capture efficiency.  Capture using Pole Face Windings instead of low energy quads is going to be tested.

The intervention on the TT10 BPMs done at the end of October solved the trajectory acquisition problems observed in TT10 except for one BPM which is still not working

It has been found that the optics of the line is hard-coded in the algorithm for the correction of the trajectory of the extracted islands in TT2-TT10 by means of the DFA. Information about the optics of the line was hard-coded preventing the correction to converge after the optics change earlier this year. The problem has been fixed now with the help of A. Franchi. Tests to correct the trajectories of the extracted islands will be performed at the end of the week.

Tests have been performed to run the deliver to the north area a CT beam with one PSB ring missing in order to understand whether the resulting temporal structure is acceptable by the North Area experiments and in particular by COMPASS. The data are been analyzed. If this time structure would be acceptable a gap could be created (missing bunch) in the circulating beam and maintained during debunching by a barrier bucket to fit the MTE fast bumper rise.

Gersende

Proposal for the test of 10 MICE RF cavities under magnetic field is progressing. Gersende contacted RP to address radiation protection issues. A formal letter of interest from MICE is required. Berkeley and Daresbury could help. CERN manpower is lacking.

Hannes

Last week: Measurements in the SPS with the low gamma transition optics have continued. 3.2x1011 p/bunch could be injected and accelerated with no visible transverse instability. Approximately 10% of the beam is not captured. Gianluigi suggested to investigate space charge effects and the possible dependence of the losses on the working point.

PS2: following the discussion a discussion with Massimo and Oliver Gianluigi suggested to conduct tracking studies with a larger number of turns (so far 1000 turns considered).

Christian

 LEIR: the losses observed at the flat-top earlier last were due to a timing problem with the transverse feedback. This has been fixed.

Christian is working on the LEIR to PS transfer line with O. Berrig in view of implementing the steering of that line with YASP.

Christian is studying batch compression schemes in the PS that could be a complement or alternative to PSB energy upgrade.

Jean-Baptiste Lallement is working on LINAC4 simulations: comparisons with different number of macro-particles is ongoing. There are still some issues in using PTC ORBIT. Christian will discuss this point with need to cross check with Michel Martini.

 

Next meeting

Monday, 29th November 2010 at 14:00 in room 354-1-001

Tentative agenda

 

 

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