Minutes of the LIS Section meeting held on 23th February 2009

Present: M. Aiba, G. Arduini, J. Barranco, O. Berrig, E. Benedetto, C. Carli, M. Chanel, A. Franchi, M. Martini, S. Maury, E. Métral, N. Mounet, Y. Papaphilippou, D. Quatraro, G. Rumolo, B. Salvant, E. Wildner

General Information (Gianluigi)

Nicolas Mounet has joined the LIS section as doctoral student from 1st February to work on the resistive wall impedance theory and on the extension of HEADTAIL to include couple bunch effects which are of interest for the LHC and the LHC Injectors.

Main conclusions of the Chamonix meeting: the number of relief valves in the short straight sections will be increased using all the available apertures. Additional apertures (200 mm diameter) will be created in the dipoles in 4 out of 8 sectors (those which are or are going to be warmed up). Two dipoles with suspected higher resistance of the splices will be replaced. This has already been done for one dipole in Sector 12 and the visual inspection has shown a lack of soldering material. The preliminary planning foresees a restart at the end of September 2009. The option of running through winter until fall 2010 has been retained. The maximum energy for the next run will be 5 TeV. The contamination of the vacuum system in case of a splice failure remains one of the major issues. The summary of the workshop sessions will take place tomorrow 24/2 at 14:00 in the main auditorium.

The invitation to the ATOP and OP days have been sent-out. Stephan noted that he had not received the invitation to the OP days. Gianluigi will contact K. Cornelis. Action: Gianluigi

The new committee structure is being set-up to take into account of the Accelerator Sector Reorganization. Two Sector-wide Executive Committees  are going to be set-up: IEFC (LHC Injectors and Experimental Facilities Committee) and LMC (LHC Machine Committees). Each group will have a representative with executive power. Most of the technical preparatory work will be performed in various working group (among other there will be working groups inheriting the work of the APC and ABOC). The structure and composition of the working groups is still being discussed.

Gianluigi asked whether it would be possible to move the time of the meeting in the afternoon in order to avoid potential conflicts with his participation to the BEMB in the absence of Oliver. It was agreed to meet from 14:00 to 16:00 every second Monday. Gianluigi will verify the availability of the room. Action: Gianluigi.

Electron cloud studies for the SPS upgrade and for the PS2 (Giovanni)

Electron cloud build-up and the resulting instabilities are considered to be one of the main limitations for the SPS in the future even in the presence of the PS2. Indeed simulations and experiments performed in 2007 indicate that the threshold of vertical electron cloud single bunch instability could be lower for the PS2 extraction energy (50 GeV) as compared to the present PS extraction energy (26 GeV). For that reason a series of studies have been started in the SPS to identify means to reduce the secondary emission yield of the vacuum chamber by means of appropriate coatings. He also gave an  overview of the plans for 2009 for this activity in the SPS.

Carbon coatings have been studied. For comparison NEG (TiZrV) coatings show a low SEY (as low as 1.1) after bake-out to 1.1, but this increases to 1.4 after venting. For that reason coatings that keep a low SEY even after venting are being studied.

Dust might be an issue for the graphite coatings. This has been studied in the laboratory. No dust has been observed even after applying vibrations and mechanical stress to the coated vacuum chamber. For that reason the vacuum chambers of some bending magnets have been coated in the SPS in order to study the long term stability of the coating.

C. Carli noted that the SEY of CNe8 seems to deteriorate in vacuum after a few hours in the presence of beam. Giovanni replied that test have been performed with another coating to verify the long term (2 months) evolution of the coating (CNe9) and the experiment did not reveal any significant deterioration (i.e. increase in the SEY) after 2 months in vacuum.

Giovanni presented also the results of electron cloud simulations performed for the PS2. Simulations indicate that the threshold SEY for the electron cloud build-up is lower than in the SPS and it is 1.2.

M. Chanel asked whether outgassing of Neon from the graphite coatings above mentioned could be an issue for the operation of low energy machines and for ion operation. Giovanni replied that measurements of outgassing were performed and did not reveal any particular issue. But this is certainly an aspect to be considered for machines other than the SPS. For new machines the design of the vacuum system could be done including the possibility of baking out the system. In this way NEG could be used as well and this could provide additional pumping speed which could be beneficial for ion operation.

Round table (all)

Michel Martini said that runs with MOCAC the IBS code developed by P. Zenkevitch and A. Bolshakov have been performed during the two weeks spent by the two Russian colleagues at CERN. A simple case has been considered (SPS with ions) but the results obtained with the MOCAC code are completely different from those obtained with known theories like the Piwinski or Bjorken-Mitingwa ones. The reason for this discrepancy is not clear yet. Michel added that G. Prior is working at the simulation of the ionization cooling for a scenario alternative to that developed at Rutherford.

Olav has introduced the modifications for the naming conventions for the PSB and PS as requested by operation.

Elena Wildner is defining the work packages for the various collaborators for the Beat-Beams study as well as the work to be done by two trainee student who will come at CERN in summer. She is also completed some work on the energy deposition for the LHC Interaction Region Upgrade.

The lattice of the PS2 is now frozen after the re-matching performed by Yannis to take into account the latest constraints imposed on the straight sections by the injection and extraction elements. A preliminary scheme for chromaticity correction  has been studied by Javier, who is now evaluating the dynamic aperture of the lattice. He is also preparing the simulations of the halo for the PS2 beam generated by space charge effects. The progress on the collective effects and in particular on space charge simulations by the US-LARP collaborators is very slow and for the moment a lot of effort is spent by them in the debugging of their simulation codes.

Nicolas has already started to work on the resistive wall theory and he is deriving the expression for the Electric and Magnetic fields. The understanding of the distribution of the electromagnetic fields is important in order to critically review the impedance measurements and their range of validity.

Christian is organizing the cold check-out for LEIR. A test period is planned in May in order to debug the machine and the controls after 1.5 years of stop. After the External Review of the PSB with LINAC4 the design of the head dump is being revised. Discussions on the detailed scheme for the longitudinal painting are on-going with the LINAC4 and PS Booster RF experts.

Masamitsu is working on  the simulation of the injection process and on the effect of the chicane bump reduction. No time dependent element strength can be inserted in ORBIT. There are two possibility to do that. Either by writing a new module or by defining a new lattice on a turn by turn basis. The latter could be implemented more easily.

Benoit has conducted measurements of the BPH/BPV beam position monitors of the SPS. The agreement of the measurements with simulations is good. The comparison of the simulations of the dipolar and quadrupolar term of the impedance for rectangular chambers with the theoretical expectations is ongoing in time domain (C. Zannini). The simulated and theoretical values agree if a scaling factor 4.4 is introduced. The reason for that is not yet clear.

Elena Benedetto is working on the beam stability issues for the accumulator (isochronous) ring for the neutrino factory. There is good agreement between HEATAIL and MOSES simulations which seem to confirm a simple scaling law proposed by Elias (see Elias' presentation at the LIS meeting on 01/12/2008). Elena is also working at the matching of the TT2TT10 line for the MTE extraction both with and without emittance exchange section. The latter must be performed with PTC as no proper description of the full coupling is available in MADX

Next meeting

Monday, 9th March 2009 at 14:00 in room 354-1-001 (please note the change of time)

Agenda:

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