Minutes of the LIS Section meeting held on 11^th February 2008

Present: M. Aiba, G. Arduini, S. Aumon, J. Barranco, E. Benedetto, O. Berrig, C. Carli, M. Chanel, S. Gilardoni, E. Métral, B. Mikulec, Y. Papaphilippou, D. Quatraro, G. Rumolo, B. Salvant

General Information (G. Arduini)

A crystal collimation experiment in the SPS has been approved by the LTC for 2009 (http://ab-div.web.cern.ch/ab-div/Meetings/ltc/2008/ltc_2008-01.html)

People from DESY are going to collaborate to the LHC commissioning and/or LHC Injector work (http://ab-div.web.cern.ch/ab-div/Meetings/ABMB/Presentations/2008/20080128/CollaborationDESY_Jan2008.pdf). R. Schmidt is the contact person at CERN. Gianluigi encouraged the members of the section to think to this collaboration as a possible mean to get help on some of the studies in the injectors.

Gianluigi asked whether there was any feedback from the LINAC4 MAC concerning the injection into the PSBooster. Christian replied that there was no comment by the LINAC4 MAC on this subject.

Optics solutions for the PS2 ring (Y. Papaphilippou) - slides

Yannis presented the status of the work on the lattice for the PS2 machine. A FODO solution and a negative momentum compaction solution are being considered.

One of the major issues for the FODO solution with positive momentum compaction factor is the need of implementing a gamma jump scheme. Although the values of the gamma jump required are not unrealistic (see last LIS presentation from Elias) but the scheme needs to be studied and the tunability of the present solution seems to be pretty limited.

The main difficulty for a solution with negative momentum compaction factor is the achievement of "low" (close to 10) absolute values of the gamma transition while respecting the constraints on maximum dispersion and beta functions. Values of 15-20i could be obtained very easily.

The major constraint on the absolute value of the gamma transition comes from the main RF system (10 MHz) the time required for RF gymnastics (splitting) to guarantee adiabaticity but it should be more carefully revised and weighted against the difficulties in obtaining a smoother optics.

It was also noted that bunch splitting would not be required if capture and acceleration is done with a 40 MHz system. It is not clear whether such an RF system can be built with sufficient bandwidth to accommodate the RF frequency swing along the ramp. Furthermore this would limit the maximum intensity on the nToF beam to 1-2×10¹² p/bunch. It is not clear whether this intensity would be sufficient in the future (taking into account of the higher energy).

It was noted that the present lattice (racetrack with a super-periodicity 2) has the drawback that a lot of systems are accommodated in the same straight section. This has the following drawbacks:

• it is more difficult to avoid systematic resonances;
• it might be difficult to satisfy all the optical conditions imposed by the different systems in one straight section.

Gianluigi noted that the compatibility of the beam dump system with the presence of electrostatic septa in the same straight section should be carefully evaluated. It might not be evident to have an external dump for a fast cycling machine as this would require guaranteeing the tracking of magnetic elements in the damp channel with energy.

PSB orbit correction (G. Rumolo) - slides

Gianluigi asked whether it is planned to verify the mechanical alignment of the beam position monitors in the PSB during the shut-down in view of the beam based alignment campaign during the start-up. Giovanni replied that the alignment of the BPMs is going to be verified before the start-up.

Christian noted that displacements of 0.2-0.3 mm might not be feasible given the precision of the survey.

Treatment of the dipole magnets in MAD8/MADX/PTC (A. Franchi) - slides

Following the discussion it has been decided that a clear warning should be written in the PS MAD-X file repository concerning the treatment of the bending magnets in MADX for bending magnets in small machines. ==> Action O. Berrig.

Before proposing additional solutions based on PTC and before modifying the PS files (e.g. by eliminating the pole-face angles in the PS bends) a clear understanding of the magnet model in MADX/PTC/MAD8 should be achieved.

After the meeting:

C. Carli noted that different version of PTC give different results. In particular with the latest version of PTC provides always values of the chromaticity different from MADX (independently from the choice of the edge angles and gradient in combined function magnets)

E. Benedetto compared the MADX and PTC output of the TT2-TT10 line for the LHC proton optics: discrepancies between MADX and PTC are observed for off-momentum and off-axis particles.

Next meeting

Monday, 10^th March 2008 at 09:00 in room 354-1-001

Agenda

General Information (Gianluigi)

Latest information on the SPS impedance (Elias)

A.O.B.

Back to Minutes