Minutes of the LIS Section meeting held on 20^th April 2009

Present: G. Arduini, J. Barranco, H. Bartosik, E. Benedetto, C. Carli, M. Chanel, A. Franchi, S. Gilardoni, P. Jackson, M. Martini, S. Maury, E. Métral, N. Mounet, Y. Papaphilippou, D. Quatraro, G. Rumolo,

General Information (Gianluigi)

From IEFC (LHC Injectors and Experimental Facilities Committee):

• Activities and studies resulting form the ATOP days have been distributed to the different working groups
• Beam loss and radiation issues will be followed-up by the MSWG (Machine Studies Working Group)
• The potential intensity limitations in the SPS for the LHC beam resulting from the beam dump kicker (MKDV) outgassing and from the electrostatic septum (ZS) ion trap sparking were briefly discussed. The results of the electron cloud simulations conducted for understanding the MKDV outgassing need to be summarized in a note urgently. Action: Giovanni.
• The impact of the failure of one or more PFW circuits should be studied with simulations first of all and possibly by machine experiments.
• The study of a long cycle with lower ramp rate for the acceleration of the LHC beam in the PS in case of failure of the rotating machine is strongly supported and a similar case should be conducted for the CNGS beam. Action: Y. Papaphilippou
• Further studies should be conducted for the SPS scraper to complement those already conducted by H. Burkhardt and to refine (if needed) the functional specifications written by G. Arduini and H. Burkhardt.

•  At the last SPSC it has been reported that after the earthquake which has struck L’Aquila (Italy) a preliminary inspection of the experimental cavern has not shown any evident damage to the detectors at the Gran Sasso Laboratory but for the time being the authorization for accessing the cavern has not yet been given. Furthermore some of the reseracher working in the laboratory had to abandon their houses damaged by the earthquake. A delay of the CNGS run has to be expected.

Gianluigi asked whether the member of the sections were interested in getting an update on the alignment work performed during the shut-down for the injectors. Most of the presents were in favour. An ABP formum will be organized and the ABP/SU colleagues will give the talk.

Gianluigi reminded the supervisors to distribute the weekly reports on the status of the machines to all the section members.

Gianluigi reminded the members of the section two deadlines:

• submission of the PAC papers to Oliver for approval by Friday 24/4.
• requests for fellows to Oliver and Gianluigi by Wednesday 6/5.

Gianluigi welcomed two new students: H. Bartosik and P. Jackson working with Y. Papaphilippou (PS2 studies) and C. Carli (LINAC4 injection into the PS-Booster), respectively. New students should be presented to Oliver when they arrive. Action: Section members

Leave (both for private and professional reasons) should be requested in EDH possibly well in advance of the starting date. Medical certificates should be presented to Delphine in case of absences due to illness.

MTE commissioning in 2008 and preparation for 2009 (Simone) - slides

Pending issues remaining from the 2008 commissioning:

• calibration of an octupole in SS39 (could be due to a orbit displacement at the magnet)
• Reliability of the high voltage connectors for KFA21. A new design has been implemented.
• BFA9: the power converter has been improved but there are still problems (also for the CT extraction)
• Longitudinal structure: A bunched beam cannot be accepted by the SPS unless the extraction RF voltage is reduced to less than 4 kV. In that case the synchronization of the kicker rise-time with the bunch gap cannot be performed and losses occur due to the finite rise-time of the fast bumpers and kickers. It has been decoded that debunching and recapture will be performed for the MTE extraction. In that respect M. Chanel asked whether signs of longitudinal instabilities have been observed during the debunching process. Simone replied in the negative (at least up to intermediate intensities). C. Carli noted that a gap could be created in the beam e.g. by injecting 8 bunches in h=9. This would leave a sufficient separation for the fast bumpers and kickers. This should be further investigated in the future. It would require some modification of the low level RF. A similar proposal (injection of 7 bunches on h=8) was done by Gianluigi but could not be implemented because it requires modifications of the PS RF low level.
• The MTE extraction was not reproducible in terms of losses at extraction. This was very likely due to an horizontal instability developing just before extraction because the horizontal chromaticity was found to be come negative at the extraction plateau. Simone reminded that the MTE extraction is performed with chromaticity very close to zero to minimize the tune spread at extraction. A small change in the radial position could also result in a change of the chromaticity due to the presence of strong octupoles. Some losses are observed close to the extraction timong although not enough diagnostics is available to determine whether the losses are occurring at extraction or just after it. Simon mentioned that there is not sufficient diagnostics to disentangle the moment of the losses.
• The optics of the TT2TT10 line needs to be matched. We will start with the optics with no emittance exchange based on the measurements performed last year.

Gianluigi asked what is the status of the instrumentation in the PS. Simone replied that are still problems with the user interface for the orbit measurement and that the wire scanners (with new electronics) are not yet operational

Round table (all)

Christian Carli mentioned that discussion with the RF colleagues are ongoing for the longitudinal painting. Gianluigi asked whether the vacuum team has conducted some investigations on the origin of the pressure rise observed in LEIR. Christian replied in the negative. He will contact them.

Elias gave a brief status of the SPS: the electrostatic septum 5 (ZS5) has to be replaced because it showed an high spark rate (this septum was replaced during the shut-down)

Elias attended the Crystal collimation workshop (24-27 March 2009). The presentations are available at: http://indico.cern.ch/conferenceTimeTable.py?confId=50840

During a presentation at the MSWG H. Damerau presented some data indicating that the LHC beam could be at the limit of stability for longitudinal coupled-bunch modes. It is not completely clear whether the phenomenon is new. Elias noted that the MTE kickers were installed during the shut-down 2007-2008. The low frequency peaks observed as a result of the impedance measurements performed on the MTE kickers could be possible responsible for this phenomenon. The issue is being followed-up by Elias. A PS imoedance web page is being built by Nicolas (http://ps-impedance.web.cern.ch/ps-impedance/).

A review of the phase 2 collimation has taken place at CERN. A promising solution has been found consisting in the installation of cryogenic collimators in the dispersion suppressors. This would require important modifications in the layout. Crystal collimators could be a possible solution as well.

The simulations for particle studio for determining the dipole and quadrupole term of the wake field for the SPS BPMs have been completed by Benoit. HEADTAIL simulations are being run to determine beam stability thresholds, tune shifts with intensity etc. including the SPS kicker impedance, the BPM impedance and the resistive wall impedance of the SPS vacuum chamber.

The partial economy mode is going to be put in operation in the SPS. This allows reducing the flat-top length for the fixed target cycle when no beam is injected.

Giovanni gave a brief overview of the PS-Booster start-up. The measured orbit is comparable to that observed in 2008 after the realignment campaign. No additional beam based realignment has been implemented. The wire scanners are snot yet fully operational: beta functions, energy are wrong and the server crashes frequently. The new turn-by-turn orbit acquisition system seems to work properly.

Sandra has simulated the transition crossing in the PS with HEADTAIL including space charge effects. The results seem to be in agreement with the behaviour expected by Elias according to a model developed last year.

Yannis said that the beam-based realignment in the PS has been completed and the results obtained are comparable with those achieved in 2007 and 2008. The behaviour of few BPMs is still being analyzed as well as their alignment offset.

BBQ seem to for most of the beams but for some of them the single-turn excitation provided by the transverse feedback is not sufficient

Gianluigi asked whether the new OTRs installed in TT2 during the shut-down are operational. Yannis will investigate what is the status of these screens.

 Work on the PS2 (Yannis and Javier) is continuing on the following subjects:

• Dynamic aperture assessment

• Tuneability studies for the lattice.

• Aperture and collimation

As previously mentioned there is a request for reducing the aperture requirements in particular for the Fixed Target beam

Nicolas is continuing the theoretical study of the resistive wall impedance.

LINAC4 simulations:

Michel Martini has resumed the simulation work for the PSB with LINAC4 and he has included the longitudinal painting using some tools provided by Christian Carli. Gianluigi asked whether the new cluster for impedance/space charge simulations is available and whether ORBIT is installed on it. Christian Carli replied in the negative. The installation should be done as soon as possible. Action: C. Carli to follow-up that issue.

Michel Martini reported that progress has been done in the definition of the task to be performed at CERN in the frame of the Neutrino Factory study. Alessandro Vivoli has rewritten in C the IBS routine of the MOCAC programme (written by Zenkevich and Bolshakov). No error has been found so far in the algorithm and the origin of the discrepancy between the MOCAC simulation results and classical IBS formulas has not been resolved yet.

Stephan reported that the SPSC is going to review the PAX proposal for installation in AD. Stephane has been nominated as referee by the SPSC for the accelerator aspects.

Next meeting

Monday, 4^th May 2009 at 14:00 in room 354-1-001

Agenda:

• General Information (Gianluigi)
• Round Table (all)

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