Minutes of the LIS Section meeting held on 7 May 2012

Present: G. Arduini, H. Bartosik, E. Benedetto, M. Bodendorfer, C. Carli, M. Fitterer, V. Forte, A. Garonna, C. S. Gilardoni, Hernalsteens,  A. Lachaize, N. Mounet, A. Molodozhentsev, Y. Papaphilippou, M. Pivi,  V. Raginel,  F. Schmidt, G. Sterbini, A. Ulsroed, R. Wasef, C. Yu

General Information (Gianluigi)

Gianluigi welcomed Michael Bodendorfer, a new staff in the LIS section. Michael is going to work on LEIR and on the upgrade of the ion injector chain.

LHC status:

The start-up after the technical stop has been rather rocky both because of  hardware problems and performance issues. Losses have been observed during squeeze and in the collision process after the technical stop. The origin is being investigated.

Gianluigi reminded that IPAC12 papers had to be uploaded on the BE server for group and departmental approval before 30/4.

Status of the short dipole studies  (Elena) - slides

Elena reminded the motivation for that study: increase the space available for the injection hardware and in particular for the injection dump presently installed in one of the chicane magnets.

Simone asked whether shorter chicane  magnets could be an option. Elena and Christian replied that this would imply stronger power converters and larger beta beating. This could be an option if we see that the impact of the dipole shortening is important but this does not seem to be the case.

The QNO quadrupoles installed in the PSB could be used to compensate for beta beating generated by the short dipoles. Gianluigi asked whether we have sufficient strength up to top energy. Elena and Christian replied that beta beating correction is needed in particular at low energy when the space charge tune spread is larger.

Elena showed that the perturbation induced by the short dipole scheme is smaller than that corrected with the QNO quadrupoles at present. Gianluigi suggested to check the polarity of the QNO quadrupoles because the error could be small if the polarity is wrong. The polarity of the QNO can be checked either by testing the polarity of the quadrupoles in the tunnel or by beam measurements verifying that the tune is not changing when we power the quadrupoles.

In the case of shorter dipoles the geometry of the line should be slightly changed.

Christian pointed out that the reduction of the length of the main dipoles could minimize the stray fields between the dipoles and the chicane magnets. The FNAL Booster and SNS suffered from that. Christian and Elena have asked the magnet people to provide an estimate of the effect of the proximity of the dipoles and chicane magnets on the field quality.

Space charge studies for PSB - preliminary status (Vincenzo) - slides

Vincenzo is running simulations with direct space charge only (no boundary conditions). This has reduced the execution time of the jobs  and in principle it could allow us to simulate a larger number of turns. Some of the simulation results seems to show some small blow-up that seems to be real. It was suggested to change the working point and see whether the blow-up rate is changing.

Short Round Table (all)

SPS

Bunches of up to 4x10¹¹ have been injected with the Q20 optics with no evident sign of instability. Space charge studies (tune scans, emittance blow-up and loss studies) will be performed with the Q20 optics. 

The preparation of an extraction from Q20 is ongoing. Dispersion beating is still observed at flat-top.

MTE

The new scheme for the gamma jump designed by Hannes has been tested in a Machine Study and left in operation after having verified that it has no negative impact on machine performance. The pattern of losses around the machine has changed but this was expected. Gianluigi mentioned that a reduction of the beam brightness has been observed after the technical stop and that larger tails seem to be present in the LHC beam. Simone replied that LHC beam emittances are similar to those obtained with the previous gamma jump scheme.

The setting-up of the Hybrid MTE extraction and in particular of the extraction bump at Septum 31 is progressing. Measurement of the tune and chromaticity during the extraction bump have been performed with the tools made available by Yannis. Corrections need to be implemented.

Next meeting

Monday, 21^st May 2012 at 14:00 in room 6-R-012

Agenda:

General Information (Gianluigi)

Summary of the PS space charge studies conducted in 2011 (Elena)

Round Table (all)

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