Minutes of the LIS Section meeting held on 29^th November 2010

Present: G. Arduini, H. Bartosik, C. Carli, S. Gilardoni, J. Gil Flores, G. Prior, Y. Papaphilippou, A. Lachaize, M. Newman

General Information (Gianluigi) 

IEFC

• No show-stopper has been identified for running in 2012
• CNGS start in 2011 has been anticipated to middle of March

The Chamonix meeting will take place in the last week of January. Decisions on the running scenarios for 2011 (energy, intensity, beta*) and on the possibility of running in 2012 will be taken there.

LHC

An MD with 75 ns and 50 ns beams has taken place form 17/11 to 20/11. A reduced vacuum activity with 75 ns spacing as compared to 50 ns has been observed but important pressure rise observed for large number of bunches. No visible heat load due to electron cloud in the beam screens for 75 ns beam (but therefore no scrubbing!). Important heat-load in the triplet-cold D1 region in particular L8. Comparison of 50ns beam behaviour during the ramp and at 3.5 TeV before and after scrubbing at 450 GeV clearly shows improvement in the straight sections (factor 7 reduction in pressure rise after 16 h of effective scrubbing) and in the arcs (heat load reduction by > factor 2).

BEMB:

• The tram line to CERN will be completed in April 2011. There are still discussions concerning the construction of a parking

• E. Cennini is the CERN link person in and outside CERN on environmental issues

• R. Bailey has been nominated Head of the CAS.

Low gamma transition optics (Hannes) - slides

A low gamma transition optics was already tested in the SPS in 1978 (D. Boussard et al. they went to tunes of 14-15 to inject 14 GeV/c protons above transition and accelerate more than few 10¹⁰ p.

The present solution (tune of 20) has a maximum dispersion: 8 m. The slip factor increased by a factor 3 at injection (26 GeV/c) and 1.6 at flat-top (450 GeV/c).

One possibility would be to increase the tune to 22 so that the slip factor is increased by a factor 2 at injection and by 1.3 at flat-top. This would reduce the voltage requirements at flat-top while still increasing the threshold for TMCI at low energy.

So far injection transfer-line optics has not been matched but the expected mismatch is small as the twiss parameters and dispersion are not changing significantly.

After loading the optics beam measurements have been performed to qualify it. Less than 20% beta beating has been measured in the H-plane. The dispersion measurements are in very good agreement with the expected values. Gianluigi noted that this could indicate the the beta beating is even lower. From the measurements of non linear chromaticity non-linear terms have been extracted.

The Synchrotron frequency has been determined at injection by measuring the quadrupolar frequency at injection for a given (unmatched) voltage.

The bunch intensity used for the measurement of synchrotron frequency was 10¹¹ protons.

No sign of instability have been observed at injection up to ~3x10¹¹

Losses (~10 %) have been observed by means of the wall current monitor by considering the time evolution of the integral of the longitudinal profile. The losses at injection diminish by increasing the capture voltage although for larger voltages slow losses along the injection plateau are observed. Gianluigi noted that this has already been seen with the nominal optics. That could be related to the larger momentum spread and dynamic aperture or to space charge.

Hannes evidenced some issues encountered with the instrumentation in the SPS:

• The sampling period for the BCT measurements is 10 ms, so the first measurement is only 10 ms after injection
• Transverse emittance measurements with the wire scanner 51995 are giving systematically lower values at the out scan. Gianluigi mentioned that these errors were known in the past and the reason understood by F. Roncarol. The correction for that was supposed to be intorduced with the new electronics. This will have to be followed-up with BI. Furthermore for this low intensity a linear wire scanner would be better suited (517).

These issues will be transmitted to the MSWG. Action: Gianluigi.

The beam has been accelerated with the low gamma transition optics. Measurements during the ramp were done but chromaticity still needs to be corrected along the ramp.

The dependence of the losses/blow-up at injection on the working point (so to compensate for possible space charge effects) needs to be studied.

The radial steering knob (taking into account the different transition energy) should be updated for next year.

The measurement of the momentum offset in combination with the measurement of the tune must be done in order to measure chromaticity during the ramp.

Round Table (all)

Antoine. The study of the PS2 MTE including the effect of various elements on capture efficiency (chirp, non-linear element strength) and the impact on aperture has been completed.

Christian. LEIR: the stripping foil had to be changed again as the stripping efficiency decreased once more.

Myriam: Stability of the trajectory for the MTE vs. CT has to be analyzed.

Gersende: waiting for a new release of MARS for simulations. The proposal for tests of the MICE RF cavities has been updated.

Yannis: FLUKA simulations for the collimation for PS2 are being done in collaboration with members of the FLUKA team. These had to be repeated as the input parameters used by the FLUKA team were not correct.

Hannes tried to run simulations of the dynamic aperture for PS2 with a larger number of turns (10000) but the results are not changing significantly

Next meeting

Monday, 17^th January 2010 at 14:00 in room 354-1-001

Agenda

• General information (Gianluigi)

• PS2 optics and dynamic aperture (Hannes)

• MTE for PS2 (Antoine)

• Round table (all)

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