Minutes of the LIS Section meeting held on 6^th August 2007.

Present: G. Arduini, S. Aumon, J. Barranco, G. Bellodi, O. Berrig, R. Bruce, R. Calaga, C. Carli, M. Chanel, F. Gerigk, S. Gilardoni, A. Lombardi, M. Martini, Y. Papaphilippou, G. Rumolo.

General information (G. Arduini)

A new machine schedule has been published for the 2007 run. It includes a CNGS run and a MERIT run towards the end of the run. (Machine schedule 2007)

The preliminary programme of the BEAM07 WS (in its latest version - modifications are expected) has been circulated.

S. Gilardoni noted that the restart of the ion injectors for LHC in 2009 after one year stop might imply some risks. G. Arduini replied that one could imagine to restart the ion injectors in 2009 well in advance to sort out any potential problem in due time.

Status of the studies on transition crossing in the PS (S. Aumon) - slides

The main outcome of the study is at present:

• The misalignment of the gamma jump quadrupoles is not sufficient to explain the observed orbit distortion at transition. After the misalignment we still see an orbit distortion at transition.
• A jump in the mean radial position (MRP) is observed when (and only when) the gamma jump quadrupoles are active.
• The jump in MRP disappears if an offset in the MRP is programmed before getting through transition. M. Chanel noted that this was the case in the past.
• There is still some discrepancy between the measured and expected dispersion.
• An orbit distortion is visible well before transition. G. Arduini asked whether we could redefine the alignment strategy in such a way that the orbit correction is performed based on the orbit distortion measured at transition. S. Gilardoni replied that in principle one should be able to correct the orbit with the high energy orbit correctors 15 and 63. Although initially it was planned the power supplies for these correctors have not been changed from mono-polar to bi-polar. It should be done this year. S. Gilardoni said that a test of the effect of these correctors at transition could be tried during the next dedicated MD when it could be possible to ask to invert the polarity if required.
• G. Arduini asked whether low energy orbit correctors could be used. S. Gilardoni replied that this could be tried but he fears that they are not strong enough.

Space charge studies at 50 and 160 MeV at the PS Booster - slides.

The measurements at 160 MeV were performed with tunes Q_H=4.21 and Q_V=4.35 and for standard parameters of the first and second harmonic cavities. Some emittance exchange is measured at 160 MeV after injection. After the 160 MeV plateau the beam was decelerated and lost at low energy. Y. Papaphilippou asked what is the expected space charge tune shift M. Chanel replied: -0.15 (H) and -0.2 to -0.3 (V).

G. Arduini suggested to investigate the emittance evolution at 160 MeV/c also for larger vertical tunes and also when the second harmonic h=2 is suppressed at 160 MeV/c. The variation of the emittance evolution as a function of tune and second harmonic could be very useful for the benchmarking of the simulations.

M. Martini said that simulations have been launched with the beam parameters provided by M. Chanel. The results (after 18700 turns, corresponding to 18.9 ms) are shown in this document. A blow-up in transverse emittance is mainly visible in the vertical plane. M. Chanel asked whether saturation is observed. M. Martini replied in the negative. He also added that the simulation is still running and that he plans to launch a long simulation during his vacations. G. Arduini asked about the type of distribution used for the simulation. M. Martini replied that he used a parabolic distribution and that the blow-up should be larger for a gaussian distribution as observed in the ACCSIM/ORBIT benchmark studies.

F. Gerigk noted that it could be interesting to have measurements also at higher energies for comparison.

M. Chanel presented also the results of the measurements performed when the tune (H or V) is moved dynamically to the integer resonance. Losses (~ 20%) are observed when crossing the coupling resonance. Y. Papaphilippou asked whether this could be due to the Montague Resonance or just simply to emittance exchange H/V. G. Arduini noted that a similar behaviour is observed when the sieve is introduced (this should reduce the intensity without modifying the transverse emittance significantly). This seems to point to the second option.

G. Arduini asked whether feedback has been received from M. Popovic and F. Ostiguy concerning the results of the simulations performed with ORBIT with different beam distributions. C. Carli replied in the negative. It was agreed that C. Carli will contact again the US colleagues to see whether they had time to look into the issue.

Status of the machines

PSB and LEIR (M. Chanel)

Concerning the alignment strategy for the PS-Booster. C. Carli and M. Chanel noted that it would be good to have a survey and re-alignment of the PS Booster during the shut-down and to make a beam based re-alignment during the start-up. G. Arduini noted that the PSB superintendent and TS/SU should be informed as soon as possible and the time for a beam-based re-alignment should be planned during the start-up. Action: M. Chanel to follow-this up.

The Early beam has been accelerated to top energy and extracted. The transverse parameters have not been measured yet because of problems with the instrumentation. This is being followed-up.

G. Arduini stressed that the main aim for this year is to have instrumentation and procedures in place for the control of LEIR from CCC, so to transfer as much as possible LEIR operation to the OP team and reduce the load on the supervisors.

PS (S. Gilardoni, Y. Papaphilippou)

The optimization of the extraction conditions in AD (radial position offset) is ongoing this morning (S. Gilardoni)

The problems with the new PFW power supplies persist and for the moment we are still running in 3 current mode.

The optics and aperture model of the BTP line is available. Some problems with PTC have been found and are being addressed with F. Schmidt.

SPS (G. Arduini)

Recent measurements of the low-frequency imaginary part of longitudinal impedance seem to indicate that the impedance has increased by 50 % from 2006. This will be followed up at the APC. Measurements of the transverse impedance are ongoing (R. Calaga, G. Rumolo).

Next meeting

Monday, 20^th August 2007 at 09:00 in room 354-1-001

Agenda

General information (G. Arduini)

Status of the machines (supervisors)

Status of Machine Studies (E. Métral)

A.O.B.

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