Minutes of the LIS Section meeting held on 22^nd September 2008

Present: M. Aiba, G. Arduini, S. Aumon, J. Barranco, G. Bellodi, E. Benedetto, C. Carli, M. Chanel, A. Franchi, S. Gilardoni, B. Mikulec, Y. Papaphilippou, D. Quatraro, B. Salvant

General Information (Gianluigi)

The New CERN Structure proposed by the Director General Designated has been approved by the Council (see official communication).

The LHC commissioning with beam on 10/9 was successful. By the evening Beam 1 was circulating for few turns and Beam 2 for a few hundred turns. By the following day Beam 2 was captured and circulating with a lifetime of few hours. In the following days the machine was stopped by some electrical (fault on 2 transformers) and cryogenics controls problem. For that reason beam could not be injected. A series of accesses were granted and remaining HW Commissioning activities mainly on Sector 34 were carried out. On Friday 19/9 during one of the last steps required to commission the main bend circuit for operation to 5 TeV an incident occurred resulting in a large He leak into the tunnel. The present situation is described in the corresponding press release.

Status of the LINAC4-PSB studies (Christian) - slides

Christian reviewed the topics recently addressed by the Beam Dynamics working group.

The schemes to produce the nominal and ultimate LHC beams with a single batch injection in the PS have been reviewed. The limitation in the extraction and recombination kicker rise-time together with the assumed scheme of injecting on h=7 in the PS impose an upper limit on the bunch length at extraction from the PS. For that reason bunches with smaller longitudinal emittance will be transferred from PSB to PS resulting in a larger space charge tune spread in the PS for at least a quarter of a synchrotron period. This scheme is of interest already now for the production of the 50 and 75 ns beams with single batch injection into the PS. A. Findlay is conducting some studies to assess the feasibility of such scheme. The synchronization PSB-PS is presently being addressed.

Elias suggested to look into the possibility of injecting into h=8 in the PS. This would soften the constraints on bunch length at extraction but this would require a batch compression from h=8 to h=7 which might be difficult to implement as the machine is almost completely filled.

The vertical beta-beating induced by the vertical focussing of the bending magnets used to create the injection bump is being considered as well. The FNAL colleagues have pointed out that this was a major issue for them in the FNAL Booster. Sector magnets could help in solving the problem but the suppression of the beta beating will be obtained only for a given bump amplitude and not during the the ramp down of the injection bump. Shaping of the poles at the entry and exit of the magnets could be also a possible solution. At FNAL the problem was mitigated by reducing the bump amplitude.

The issue of the injection steering has been addressed as well. This allowed finding an error in the injection steering matrix in the PSB. This has been corrected now.

Benchmark studies are continuing. Michel Martini has sent some ACCSIM input files to Fred Jones so that he can investigate the differences observed between ACCSIM and ORBIT. No feedback has been received so far. 2 or 3 new nodes for impedance and space charge studies will be bought on the LINAC4 budget. The ORBIT programme will be transferred from the OPLAPRO cluster (whose future is uncertain) to the new impedance/space-charge cluster which will be used by ABP and RF.

More emittance measurements data (at shorter time intervals) are required to quantify the temporal evolution of the emittance at 160 MeV/c and provide a more detailed comparison with simulations.

Round Table (all)

PSB (Michel Chanel)

The studies on the instability observed on Ring 4 have revealed a cabling problem in the transverse damper in Ring 4. An H and V plate were connected to the horizontal damper system. Christian noted that the vertical damper is not used and therefore the existing configuration was equivalent to have a reduced gain. After the re-cabling the instability has disappeared. After the meeting Michel Chanel reported that the same cabling error has been found on Ring 2. It is not clear since when this situation exists.

Some (so far) unexplained coupling between the radial position of ring 1 and ring 4 has been observed.

PS (Simone, Yannis)

The tune measurement is still not working and the excitation with the transverse damper was not working because of a cooling problem. The lack of a tune measurement is blocking the progress in the setting-up of the MTE for the SPS. After the meeting Simone communicated that the tune measurement was working (although only form a Windows console) as well as the damper excitation.

SFTPRO and CNGS are now delivered to the SPS with h=8 and debunching so to allow running the MTE cycle for physics with h=8 if needed. Measurements of the twiss parameters and dispersion in TT2 will be performed this afternoon by Simone and Elena.

Next meeting

Monday, 6^th October 2008 at 10:00 in room 354-1-001

Preliminary Agenda

General Information (Gianluigi)

Round Table (all)

A.O.B.

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