Minutes of the LIS Section meeting held on 26th January 2009

Present: G. Arduini, J. Barranco, O. Berrig, C. Carli, M. Martini, E. Métral, Y. Papaphilippou, G. Prior, D. Quatraro, B. Salvant, E. Wildner, C. Zannini

General Information (Gianluigi)

Gianluigi reminded the deadline for the submission of the requests for summer students (Friday 6th February 2009 to Oliver, Delphine with copy to Gianluigi).

G. Roy is looking at the implications of the "Two persons rule" for BE and asked whether do we seen any implications for ABP. During the meeting it was concluded that there was no implication.

Gianluigi reminded that it has been decided to have a lead ion run in 2009 in order to complete the commissioning of the low level RF system in the SPS. He asked whether the front-ends that were taken from LEIR last year have been re-installed. Christian will follow that up.

Gianluigi announced that the visit (and seminar) of V. Kornilov has been cancelled as he is ill.

An LHC Performance Workshop will take place in Chamonix form 2nd to 6th February. The main focus will be the definition of the strategy for the repair and it impact on the LHC start-up and physics schedule. Gianluigi will attend the meeting during the whole week.

It has been decided to change the two dipoles that showed a resistance higher than nominal in Sector 12 and Sector 67. The dipole in Sector 12 has already been inspected and a poor welding has been detected in the splice between two coils.

Round table (all)

Gianluigi introduced two new members of the team: G. Prior and E. Wildner and asked each member to give a short presentation of his/her activity

O. Berrig is responsible for the optics and aperture DB for the machines and transfer lines of the PS-SPS Complex. All the information is available on the web ( http://cern-accelerators-optics.web.cern.ch/cern-accelerators-optics/ ). J. Papaphilippou and E. Wildner asked whether it would be possible to add a link to the lattice of the machines for the Beta-Beam study and the PS2 which already exist on the web. Olav replied in the affirmative.

Elena Wildner is responsible for the Beta Beams work package in the frame of the european programme EuroNu. She will give a presentation on this study at one of the next LIS meetings.

Michel Martini is involved in LINAC4 to PSB space charge studies, Neutrino factory studies (in particular the front-end) and in IBS simulations for the CLIC damping ring. Two russian visitors are presently at CERN to help in installing and running the programme MOCAC which should allow conducting simulations of this phenomenon. The present theories developed by Piwinski and Bjorken-Mitingwa can only treat gaussian distributions, on the other hand it is important to understand whether non-gaussian tails can develop as a result of intra-beam scattering as this will have an important impact on the design of the damping rings.

In reply to a question from Elena Wildner, Michel said that the space charge simulations for the LINAC4 to PSB studies are conducted with the programme ORBIT. Past experience with the ACCSIM programme revealed some bugs that are presently being studied by F. Jones but for the time being there is no news form him on that subject. Elena Wildner noted that ACCSIM was used as well for space charge simulations for the Beta Beams study.

G. Prior, fellow under Michel Martini's supervision is going to work on the front-end for the neutrino factory and in particular on the collection of the muons.

Yannis Papaphilippou is PS supervisor, he is also involved in the PS2 design study, CLIC damping ring studies and, as a consequence of the Sector 34 incident, on the slot assignment of the short straight sections. The PS2 has a negative momentum compaction factor lattice. Recently the requirements on the lattice of the straight sections resulting from the injection, extraction, etc. have been finalized and Yannis could finalize the matching of the lattice. Javier Barranco, PhD student under Yannis' supervision is working at the collimation system for the PS2. The simulations have been done so far for the previous version of the lattice. Work is starting on the new lattice. Javier is also evaluating the tune spread and emittance blow-up resulting from space charge at low energy. These simulations are performed with ORBIT.

Elias Métral is SPS supervisor, Machine Development Coordinator and he is following-up (together with Giovanni Rumolo) the issues related collective effects in the PS-SPS Complex. He is also in charge of the study of the collective effects in the LHC. He took the occasion to remind the LIS members that the deadline for the submission of the MD requests is 20th February. He has made quite some progress in the understanding of the low frequency behaviour of the resistive wall impedance. Some work has also been recently conducted in the study of the dependence of the rise time of the TMCI on bunch intensity when this is well above the threshold for the onset of this instability (done in collaboration with Elena Benedetto). This is of interest for neutrino factories which include isochronous rings for which the threshold for the instability is very low because the slippage factor eta is very low. Elias is also working with Carlo Zannini, Giovanni Rumolo and Benoit Salvant at defining and validating the steps to be performed for the wake-field simulations in order to extract the dipolar and quadrupolar components of these transverse fields. This distinction is required in order to provide the input to the HEADTAIL simulation code used to study the development of instabilities as a result of the interaction of the beam with the machine coupling impedance. Simulations have been performed by Carlo with Particle Studio for simple cases (rectangular vacuum chambers) in order to benchmark the simulations with theoretical results. The relative values of the horizontal and vertical impedance are correct but the absolute value differs by a factor 4.4 from theory. This is being investigated.

Diego Quatraro is a PhD student working under the supervision of G. Rumolo to study the collective effects non-relativistic regime as in the PS Booster. He has developed a formalism for the longitudinal resistive wall impedance in the non relativistic case and he has obtained an approximation of the transverse resistive wall impedance in the low and medium frequency range (long bunches). A similar study is being conducted for a broad-band impedance. Diego, together with Giovanni and Michel Chanel are also studying an instability observed at low energy in the PS Booster. The features of the instability (the spectrum is peaked around 6 MHz) and the instability occurs at well defined timings in the cycle seem to point to a narrow-band impedance. Michel Chanel suspects the extraction kickers as possible responsible for the offending impedance. Diego suggested that measurements could be taken as a function of the chromaticity and of the tune in order to collect additional information about the nature of this instability and the possible origin. Gianluigi encouraged Diego to summarize the observations conducted so far and the plan of studies in 2009 in an MD note. Action: Diego. 

Andrea Franchi is working as a fellow under the supervision of M. Giovannozzi for the commissioning of the Multi-Turn Extraction. One of the problem remaining at the end of the run was the non-reproducibility of the extraction in term of losses. A preliminary analysis of the data seems to indicate that the horizontal chromaticity was negative during the extraction plateau and this could result in instabilities that could explain the non-reproducibility of the performance. The rather large transverse emittance measured in the transfer line from PS to SPS could be the result of that as well.

Next meeting

Monday, 23rd February 2009 at 09:30 in room 354-1-001 (please note the change of time)

Agenda:

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