Minutes of the LIS Section meeting held on 20th June 2011

Present: G. Arduini, H. Bartosik, C. Carli, S. Gilardoni, A. Lachaize, M. Newman, G. Prior.

General Information (Gianluigi)

The ABP group meeting will take place on Tuesday 28/6 and it will be followed by a barbecue (weather permitting).

 Gianluigi reminded that travel reimbursement should be requested within 6 months.

A concerted work stoppage has been called by the staff association on Wed 22/6 from 08:30 to 12:00. During that time the accelerators will be put in stand-by for safety reasons as it was done already in the past in analogous occasions.

LHC: An integrated luminosity of more than 1 fb-1 has been achieved. The last week has been very difficult with a lot of technical issues affecting the availability of the machine.

From the Research Board.

A Machine Study Working Group meeting has taken place last Friday to address the issues with the wire scanners in the PS-SPS Complex and review the results of the campaign of measurements conducted in the last 2 weeks. Some of the issues have been solved but hardware problems remain to be addressed:

Simone mentioned that at present only the data are collected only during the IN scan and the wire is returning to its OUT position after the scan. So it would be possible to limit the number of scans by having a single movement per acquisition and by retrieving the data also during the OUT scan.

Simone announced that the yellow report on the first 50 year of the PS was published. He asked what was the status of the annual report. Gianluigi will inquire.

Recent MD results for nominal and low gamma-t optics (Hannes) - slides

A working point scan has been performed looking at the dependence of the losses as a function of the working point. Third order resonances are clearly seen both for the nominal and low gamma transition optics. Gianluigi noted that individually powered normal sextupoles (used for the slow extraction) are available for compensating the normal sextupole resonance.

In 2010 the beam emittance had to be blown-up in the PS to get stable beams on the nominal optics at high bunch population. Gianluigi asked whether this could be due to the larger tune spread induced by detuning with amplitude for larger emittances and asked whether the detuning with amplitude has been measured for the two optics this year. Although bunch population of up to 2.5x1011 p can be accelerated this year with the nominal optics losses are larger with the nominal optics for a given bunch population. Gianluigi asked whether the chromaticity settings for the nominal optics and the low gamma transition optics were the same. Hannes and Yannis replied that this should be verified and it could be that the chromaticity was larger for the nominal optics cycle.

Christian noticed that in the plot showing the dependence of the emittance blow-up as a function of the vertical tune the points with larger blow-up seem to correspond to larger bunch populations. Gianluigi suggested to measure the intensity and emittance of the beam coming from the PS so to measure losses and emittance blow-up right at injection as it is not clear what is the time scale of the space charge phenomena.

Gianluigi noted that in 2007 during the commissioning of the SPS with ions where tune spreads as large as 0.08 were expected in the vertical plane operation with higher vertical tune (close to 0.25) proved to minimize the emittance blow-up at injection energy.

 

PS Upgrade plans, issues and status (Simone) - slides

The transverse feedback in the PS is not yet operational. It is expected to have it available in autumn. The skew quadrupoles will be upgraded and used as a reserve in case of problems with the transverse feedback. Gianluigi and Christian noted that the specifications of the PS transverse damper are not more challenging than those of the transverse feedback in other machines like the PS-Booster, SPS or LHC. In the past there was not a strong push to get it operational as it was not considered to be necessary (and indeed it was not) for the operation of the LHC beams with nominal bunch population. This is now changing because the bunch intensity is going to increase significantly.

The bunch population limit shown in the parameter space charts correspond to the power limit on the SPS cavities.

Gianluigi found the specification for the losses in the SPS (10%) too conservative. This is larger by a factor 2 as compared to what is accepted in the PS and losses occurs at higher energy.

Working point scans have been performed by E. Benedetto. The measurements were performed with Landau Octupoles ON. The measurements will have to be repeated with octupoles OFF.

The PTC-ORBIT model for the PS is available, but no simulations in the presence of space charge effects have been started.

Transient beam loading on the high frequency cavities is affecting the LHC beams. Gianluigi asked whether a feed-forward system is foreseen for these cavities. Simone replied in the affirmative. The feedback on these cavities will be upgraded as well as the short-circuiting of the 10 MHz cavities gap

Elena, Gersende and Sandra are working for the PS project but need more support for collective effects.

 

Round table discussion (all)

Hannes

Electron-cloud simulations for the SPS are ongoing to compare the threshold electron cloud density for the onset of the electron cloud instability for the nominal and low gamma transition optics. The low gamma transition optics is superior in performance to the nominal optics particularly near threshold for the onset of the electron cloud build-up.

Christian

Another issue has been identified for the transfer line from LINAC4 to PS-Booster. A wrong magnet type (H-magnet) was used (instead of a C-type magnet) at the bifurcation of the transfer line towards the PSB on one side and the measurement line on the other. The magnet is not yet ordered and it will be re-designed.

The new layout is converging.

Time evolution with ORBIT-PTC is implemented. Tested with single particle. Michel Martini is going to run some space charge simulations with the full injection process with all the parameters varying. The effect of the imperfections of the chicane magnets needs to be Introduced and studied. Some preliminary estimates of the imperfections are available.

MTE (Simone, Antoine, Myriam)

New extraction scheme with electrostatic septum is being studied by Myriam. It is possible to close the extraction bump but the kick enhancement quadrupoles are needed.

It is not yet clear why experimentally the islands collapse when the bump in 31 is activated. A measurement of the non-linear chromaticity has been done and the bump 31 has no significant effect on it and it should be possible to compensate the induced tune shift. The experimental test of the extraction using the electrostatic septum should be performed soon.

It is now important to have a reliable turn-by-turn orbit measurement to measure the evolution of the islands.

Antoine is measuring the optics at 2 GeV and building the non linear model of the PS at 2 GeV. It is planned to capture the beam at 2 GeV in order to study the dependence of the fluctuations as a function of energy by comparing the behaviour at 2 and 14 GeV. Also for this the turn-by-turn orbit measurement needs to be operational. Gianluigi suggested to study the slow extraction at 2 GeV profiting of the non-linear model. This would be useful for evaluating the feasibility of extracting low-energy ions to the PS East Hall for radiobiological applications.

Gersende

There is still a difference in the neutrino yield calculated with the CERN and BNL MARS versions (30% difference). This could be an issue with the random number generator. Gianluigi suggested to talk to E. Macintosh and H. Renshall.

Yannis

Turn-by-turn orbit data analysis tools being set-up. The tools are being used in the PS (for MTE) and in the SPS for the phase advance measurements vs. intensity for impedance localization.

Next meeting

Monday, 4th July 2011 at 14:00 in room 6-R-012

Agenda

 

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