Minutes of the LIS Section meeting held on 5^th March 2007.

Present: M. Aiba, G. Arduini, J. Barranco, G. Bellodi, E. Benedetto, O. Berrig, C. Carli, M. Chanel, A. Franchi, S. Gilardoni, M. Juchno, A. Lombardi, M. Martini, S. Maury, E. Métral, Y. Papaphilippou, G. Rumolo, B. Salvant, R. Scrivens, G. Smirnov

General information (G. Arduini)

G. Arduini noted that the there has been a request from CO to verify a list of power converters that apparently are no more used. If no explicit requirement is done the controls of these power converters will be no more guaranteed. M. Chanel is looking into the PSB list..

Linac 4 beam parameters (A. Lombardi) - slides

C. Carli noted that there is no clear separation between the chopped and un-chopped part of the beam. A. Lombardi noted that only ~3 per mille of the chopped beam can make it through the chopper (this fraction is calculated taking into account possible errors).

 The beam coming out of the LINAC4 is approximately "spherical" in transverse phase space. This needs to be taken into account in the space charge simulations (this is not presently the case). Action: M. Martini.

A. Lombardi noted that the expected energy jitter inside a LINAC4 pulse is of the order of 270 keV r.m.s. (i.e. the energy r.m.s. energy jitter among bunches), while the phase jitter is expected to be 1.8 degrees (at 352 MHz). It is expected that the main jitter occurs inside the pulse and not from pulse-to-pulse. It is also expected that the pattern of the energy modulation from cycle to cycle will be different from pulse-to-pulse and therefore it is not possible to reduce the jitter with a feed-forward.

A. Lombardi mentioned that the for the time being the transfer line from LINAC4 to PSBooster has been designed assuming that the Twiss and dispersion parameters at the PSBooster injection are the same as those presently in operation. She also added that, due to space charge, the centroid and envelope dispersion are different. A. Lombardi added that different options concerning the longitudinal characteristics of the beam at PSB injection are open. C. Carli noted that the convention concerning the sign of the dispersion must be carefully verified as the beam in the PSBooster is circulating anti-clockwise. He also added that the choice of the parameters at injection and in particular concerning the dispersion depend on the choice of the painting scheme. Action: C. Carli and M. Martini to define the Twiss and dispersion parameters at injection in the PSB for finalizing the transfer line design. The sign convention for the dispersion should be also verified.

The present design of the high energy part of the LINAC4 is based on an operating frequency of 704 MHz, this choice optimize the operation of LINAC4 as SPL injector but not necessarily might be the optimum choice for the injection into the PSB. G. Arduini asked whether this could have an impact on the threshold for the microwave instability in the PSB right at injection. C. Carli and M. Chanel noted that the pumping ports have been shielded in the past to increase the threshold for the onset of the microwave instability and that the bunch repetition frequency is in any case 352 MHz, although this issue should be investigated. Action: G. Arduini to contact E. Shaposhnikova to get help from AB/RF in that respect.

High intensity beams in the PSB (M. Chanel) - slides

E. Métral asked whether the horizontal and vertical coherent tune shifts are similar. M. Chanel replied in the affirmative. The reason for that being the circular shape of the vacuum chambers in the PSB in most of the machine.

G. Arduini asked whether the losses that are visible at low energy occurs below 160 MeV. M. Chanel replied in the affirmative.

M. Chanel noted that most of the losses occurring at low energy are due to the space charge tune spread and the overlap with the integer resonance. He also noted that the most of the blow-up is occurring in the vertical plane where the space chare tune spread is larger, as indicated by the comparison of emittance measurements with and without the sieve as a function of the number of injected turns. It seems also that for high intensity beams the de-coherence time of oscillations is much larger than for low intensity beams. E. Métral noted that this has already been observed in simulations and that this could be the result of the separation between the coherent and incoherent tune spreads and the absence of overlap between them.

M. Chanel noted that there might be indications of electron cloud build-up along the bunch and head-tail motion. He added that no transverse feedback is required for the first 100 ms and then only the horizontal one must be switched ON for high intensity beams.

G. Arduini asked whether the chromaticity can be corrected in the PSBooster. M. Chanel replied in the negative. G. Arduini replied tat this could be an issue for the psace-charge simulations with ACCSIM as the chromatic effects are not taken into account in the tracking.

Next meeting

Monday, 19^th March 2007 at 09:00 in room 354-1-001

Agenda

General Information (G. Arduini)

Transfer line fromLINAC4 to PSBooster (G. Bellodi).

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