Minutes of the LIS Section meeting held on 16^th April 2007.

Present: G. Arduini, S. Aumon, J. Barranco, E. Benedetto, O. Berrig, C. Carli, M. Chanel, A. Franchi, S. Gilardoni, M. Juchno, E. Métral, M. Martini, S. Maury, Y. Papaphilippou, G. Rumolo, B. Salvant, G. Smirnov.

General information (G. Arduini)

With the start-up of the machines we will have regular short presentations on the major issues on the running machines by the LIS Machine Supervisors.

Model of the losses in the PS and modelization issues (J. Barranco) - slides

J. Barranco is a doctoral student working under Y. Papaphilippou's supervision. He is going to work on the study of the losses and collimation in the PS2 (replacement of the PS) machine. in order to prepare the tools for such a study he is simulating the loss distribution resulting from the interaction of the beam on the electrostatic septum (Molybdenum blade - ~200 microns thick) during the Continuous Transfer extraction at 14 GeV/c.  This is one of the major source of losses in the PS for the high intensity beams as evidenced by S. Gilardoni.

The simulations performed by S. Gilardoni were based on a simplified aperture model of the PS machine (standard vacuum chamber everywhere) and on a detailed model of the interaction of the particles with the Molybdenum septum.

The tools used for the LHC have (SIXTRACK with detailed aperture model) have been used by J. Barranco for the present analysis in conjunction with the distribution of the particles at the exit of the septum as generated with MARS.

The simulation (on turn tracking) represents well the measured losses with the exception of those measured in Section 85. In general there is also an offset among the simulated and measured losses. The latter seem to occur always 1 or 2 sections downstream as compared to the simulated ones. This could be the result of the showers generated by the protons emerging by the septum when interacting with other elements of the machine. The latter phenomenon is not taken into account in the simulations: the showers generated in the interaction of the protons with the elements of the machine (except the septum) are not taken into account.

J. Barranco noted that the kick provided by the electrostatic septum on the particles emerging from the Molybdenum foil towards the "outside" of the machine is not taken into account. G. Arduini and S. Gilardoni noted that this could be added by taking into account the longitudinal position at which the particles emerge from the septum. In that case the integrated electric field seen by each particle could be estimated and added to obtain a more realistic distribution to be used as input for the tracking. The simulations show that the losses in SS 5-9 can completely be transferred to SS 75 by using a different pair of quadrupoles (QKE25 and 73) instead of (QKE5 and 25) to increase the beam size at the electrostatic septum 31 as proposed by S. Gilardoni. another option consists in using both pairs of quadrupoles in order to share the losses between Section 9 and section 75.

G. Arduini asked whether the tracking over more than one turn has been attempted. J. Barranco replied in the affirmative but no significant difference was observed.

G. Arduini asked whether the simulations have been performed  also for the case in which the Fast Bumpers (BFA) are ON. J. Barranco replied in the affirmative but again no significant difference was observed.

Attempts have also been done to simulate the losses using the K2 routine in SIXTRACK and by tracking the particles over several (~1000) turns. In that case the losses in 8-9 appear as well as the losses in section 41-45. S. Gilardoni noted that this observation is similar to what was observed by O. Berrig in when tracking "beamlets" with a kick corresponding to ~+/- 2 mrad at the electrostatic septum. It must be noted that only symmetric collimators can be inserted in SIXTRACK and there is not a way to simulate a thin septum at present. G. Arduini noted that an asymmetric aperture could be represented by inserting a large aperture and an offset.

For the moment the cross-sections for Molybdenum are not available in PTC but J.-B. Jeanneret is willing to help to introduce them and to help in the investigations on the range of energies in which K2 is applicable. For PS and PS 2 we need to have a good model for the energy range 1-100 GeV.

At present SIXTRACK does not deal properly the edge effects and 'ad hoc' thin elements have been introduced to represent them. PTC on the other hand can deal with these effects correctly but it is not well adapted for extensive tracking or for dealing with detailed loss maps for this one possibility would be to slice the magnets and to introduce additional markers for having additional observation points but Y. Papaphilippou noted that it is not clear whether this would still provide a correct representation of the edge effects. S. Gilardoni suggested to "transform" the thin multipoles introduced by O. Berrig to represent the wide PFW circuits into markers to have additional observation points.

Once the issues concerning K2 and the slicing are well understood J. Barranco will contact E. Forrest and P. Skowronski to see whether the required modifications (inclusion of K2 in PTC, thin lens model in PTC, multiple observation points, etc.) can be introduced in PTC.

M. Chanel asked whether the BLM loss pattern showed by J. Barranco is an integral over all the cycle. S. Gilardoni replied in the affirmative but he added that the losses at extraction have been measured and are mainly located in SS 8-9, 15-16, 30-33, 41-45, 57, 85, 98.

Status of the PSB (M. Chanel).

High intensity has been achieved without problems.

A low intensity beam has been delivered to the PS for the setting-up by Friday 13/4 morning.

During the setting-up the transformer of the injection line were not working properly as a result of an "upgrade" of the electronics, this also prevented the correct operation of the magnetic pick-ups for the measurement of the beam position in the line. Steering had to be done initially with the screens. The problem was solved by re-installing the old electronics.

Since last year the orbit shows large distortions (15-20 mm H and 10 mm V - peak-to-peak). Measurements of the orbit should be taken in order to find candidates for a "voluntary" misalignment (or realignment) of main quadrupoles for reducing these distortions. O. Berrig, C. Carli and B. Mikulec are contributing to that. For the time being there is a problem with the software for the orbit acquisition: it does not allow to change the timing of the measurement.

Status of the PS (S. Gilardoni)

The PS has taken a low intensity beam, accelerated it and extracted to D3 on Friday 13/4. During the week-end no beam has been taken because of a problem with an incorrect status of a vacuum valve (which was removed and re-installed in a different section as part of the modifications for the New Multi-Turn Extraction).

Measurement of the orbit at 10 GeV will be performed on Wednesday 18/4 so to provide the survey team with the required main magnets misalignments by Friday 20/4. The magnets will be moved during the following week. M. Chanel suggest to "synchronize" the PS and PSB alignment work next week as two different teams are involved.

Next meeting

Monday, 30^th April 2007 at 09:00 in room 354-1-001

Agenda

General Information (G. Arduini)

PS2 status (Y. Papaphilippou)

TMCI at SPS injection: HEADTAIL vs. MOSES (B. Salvant)

Status of the machines: PSB-PS (M. Chanel, S. Gilardoni, Y. Papaphilippou)

A.O.B.

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