Minutes of the LIS Section meeting held on 8 ^th October 2012

Present: Androula Alekou, Gianluigi Arduini, Hannes Bartosik, Christian Carli, Vincenzo Forte, Adriano Garonna, Simone Gilardoni, Cedric Hernalsteens, Meghan McAteer, Yannis Papaphilippou, Adrian Ulsroed, Raymond Wasef

General Information (Gianluigi)

Windows XP is not going to be supported any more by IT form the beginning of next year. Gianluigi should be informed if anybody has an old PC that cannot be upgraded to Windows 7.

A new administrative circular (n. 4) has been released concerning the procedures and rules for driving a CERN car. An electronic form is now available in EDH to request the permission to drive a CERN car.

In spite of the information given by HR at one of the meeting organized by the Accelerator and Technology Sector responsible for the Technical and Doctoral Students for the moment the Department does NOT reimburse the travel and per-diem for students visiting their home university.

LHC:

The start-up of the LHC after the Technical Stop has been rather rocky with cryogenics problem and vacuum issues following the changes of one of the injection kickers in point 8. A short test performed with 25 ns beams has shown that important pressure rises in the kicker area in point 8 are observed already after injection of a single train of 72 bunches. As a result of that the scrubbing run has been postponed as it would not be efficient. Following the above short 25 ns test physics has been resumed and 1.1 fb^-1 has been delivered. The integrated luminosity is now 16.4 fb^-1 for the two major experiments. A machine development session has now started.

IEFC:

• Status and plans for HIE-ISOLDE: Plan to deliver beam in 2015. There is progress the performance of the RF cavities while there is a delay (9 months) for the cryogenics line specification and tender. This could result in a delay of the linac commissioning with beam and in a possible interference with the ISOLDE start-up. Civil engineering is nearing completion and the installation of the main services will start.

• DIRAC dismantling and plans for zone upgrade
• Responsibility for experimental magnets
• Report on the status of the PSC40-78 RF cavity: The origin of the fault leading to the damage of the amplifier of the cavity is not understood. All the interlocks seem to be functional. The cleaning of the RF port on the cavity has taken place during Technical Stop 3 and a new amplifier is being built and installed possibly during the Christmas
 
• Christmas break requirements for accelerators: Need to go back to next IEFC as the plan was based on the assumption that the no cooling circuit cannot be emptied and therefore a minimum heat load must be kept to avoid the circuit freeze. This seem to pose serious problems for the PS main magnets and POPS.
• Report from the Research Board: PSB and PS experimental areas will continue until 17/12. CNGS will stop on 3/12. The North  Area will run with ions until 17/12. End of LS1 (not final yet) Operation for physics is supposed to start in the PSB on 15/6, in the PS on 15/7. The SPS start-up is delayed until LHC requires beam (likely to be delayed to beginning to 2015). There is some pressure to get beam to the North Area in 2014

Round Table (all)

MSWG (Simone)

Wire scanner new design. A new design of the tank aiming at a reduction of the impedance should be studied. It is not yet clear whether the recent wire breakages on the SPS wire scanner 519 are due to the interaction with the beam or due to trapped modes when the wire leaves the parking position. The possibility of using synchrotron light to measure at least the evolution of the emittance along the batch could be an interesting alternative (proposed by Giovanni Rumolo). Gianluigi has mentioned that to the BI colleagues.

The Ionization Profile monitor is not available in the SPS. The power converter of one of the compensator magnets used to compensate the orbit distortion produced by the magnetic field at the BGI is not working.

The PS damper is now operational along the whole TOF cycle in the horizontal plane. The electronic card for the vertical plane should become available next week. Cedric asked whether it is planned to reduce the coupling at injection which could lead to interferences between the dampers in the two planes. Simone replied in the affirmative but this will require reducing the chromaticity and using the damper to stabilize the beam at low energy (e.g. for the LHC beam)

ELENA (Christian)

ELENA design report completion postponed to beginning of next year. Discussions are ongoing for the design of the wide-band pick-up for longitudinal Schottky diagnostics and for the RF low level diagnostics.

IBS estimates are still missing for the ELENA machine. Fanouria could provide this type of results. The simulation program she uses can determine the beam transverse distribution and does not assume a Gaussian distribution. Christina mentioned that at present large tails are observed in AD after cooling. This could be due to IBS and it would be important to provide and answer. Some benchmarking between simulations and experiments could be done in AD.

PSB (Meghan)

The turn by turn acquisition of the beam position is not yet working properly. No oscillations are observed in the beam when kicked with the tune kicker. Gianluigi suggested to check whether the oscillations is visible from the damper pick-ups. The possibility of changing the tune of the machine to change the phase advance between pick-ups is being considered. With the present cabling configuration it is possible to reduce the integer tune by one unit at low energy or to increase it by half unit by using the Qstrips.

It must be noted that in the past (before 2005) the PSB was operated with a vertical integer tune of 5 (now 4 as in the horizontal plane). The main reason for reducing the integer tune was to avoid the systematic resonance 3Q_V=16. In the discussion it was noted that measurements and simulations should be repeated for the old working point but this would require recabling the quadrupole power supply connection. Christian noted that it would be desirable to have a bi-polar quadrupole power supply as this could make this kind of tests much easier. Simone suggested to conduct the test with the old working point in 2013.

Space charge studies in the PSB (Vincenzo)

Vincenzo reported that additional machine studies have been conducted in the PSB. Tune scans in the vertical plane have been performed with constant horizontal tune. He reported that no loss was observed at 160 MeV when switching off the multipolar corrector. The bunch intensity was 1.7x10¹² p. Christian and Gianluigi suggested to verify what was the current of the correctors at 160 MeV and asked whether the current was reduced to zero also at injection and what were the results. Vincenzo will verify that.

Vincenzo is introducing the aperture in the PTC-ORBIT simulations (for the moment the beam scope aperture only). The scattering foil is not yet implemented. Gianluigi asked whether simulations have been run with the short dipoles in the injection area. Vincenzo replied in the affirmative and that the emittance blow-up is small. Gianluigi suggested to have a presentation on the status of the beam experiments (including the above observations) and of the simulations (including aperture and short dipole effects) at the next section meeting. Vincenzo agreed.

Vincenzo mentioned that e is presently using particle distributions generated from measured tomoscope data for the space charge simulations.

LAGUNA-LBNO studies (Androula, Yannis)

The fast extraction of the beam form the SPS point 2 using the injection kicker MKP is being studied at 100 GeV. Some coupling is observed. Gianluigi suggested to consider the option of using the extraction kicker in point 6. In the past the phase advance between point 6 and point 2 could be adjusted to be a multiple of 2 pi. Hannes and Yannis noted that this option might not work because of the presence of horizontal aperture bottle-necks in point 1.

Yannis mentioned that among the possible options for the high intensity operation of the injectors for LAGUNA the ide of injection in the SPS at 20 GeV with a low gamma transition optics could be used to avoid crossing transition.

LAGUNA includes a high power version using SPL with a high power PS. Yannis is studying a version with superferric magnets (similar design as those developed for GSI-FAIR). This would give a smaller ring and low power consumption. A first lattice is based on the PS2 lattice with a three fold symmetry ring.

Masamitsu Aiba will come to CERN and he will present his  previous work for an high power accumulator. He will present this during an ABP forum on Thursday 18/10 at 11:00.

MTE (Antoine, Cedric, Simone)

The filter proposed by BI to eliminate bad acquisitions from the turn-by-turn trajectory acquisition in the PS allows to filter-out wrong acquisitions resulting from a saturation of the sum signal. About 30% of the acquisitions are discarded in that way. The proposed filling scheme to avoid the saturation of the sum signal did not improve the situation.

Next steps:

• Re-establish the capture and extraction and measure oscillations in trajectory at extraction and in the mean time continue with the trajectory measurements at extraction.

• Optimization of the extraction trajectories in preparation for the installation of the dummy septum will be performed.

• Tune and chromaticity measurements and correction during the raise of the slow bump in 31 will be performed in preparation of a test of the hybrid extraction in 2013.

LEIR for radiobiological applications (Adriano)

The verification of the calibration curves for the sextupoles and pole-face windings and the maximum current acceptable by these circuits is ongoing with magnet people

Adriano is facing some problems when matching the machine parameters (extraction bump, tune, chromaticity) during the extraction

Space charge studies in the PS (Raymond)

Raymond is going to study space charge effects in the PS with extreme space charge tune spread (up to 0.6). These large values are obtained by bunch compressions.

PTC orbit simulations have been performed over 25 ms including magnetic errors. The experimental results showing losses close to a skew sextupole resonance cannot be reproduced by the simulations so far. Magnets misalignments are not yet included in the model. Simone mentioned that the it is not clear whether the latest results for the main magnet survey are included.

Simone and Raymond are verifying the possibility of re-installing the skew sextupoles that were used in the past to compensate a skew sextupole resonance and that were removed in the eighties.

In order to proceed with a measurement of the resonant driving terms in the PS we need to correct the chromaticity.

SPS and Q20 (Adrian, Hannes, Yannis).

The extraction parameters at the beginning of the TT2-TT10 transfer line are being measured in view of a possible re-matching of the line. For the moment only the dispersion and dispersion derivative have been measured using the OTRs and pick-ups in TT2. The measurement of the twiss parameters are not yet conclusive. Gianluigi suggested to use also the TT10 BPMs and the SPS BPMs (first turn) for the dispersion measurement.

Tail measurements have been performed by Lene with the nominal extraction bump from the PS. Measurements will have to be performed also with the new extraction bump for comparison. Twiss and dispersion will have to be measured as well for both extraction bump configurations. It is planned to complete these measurements after the LHC MD as the LHC is going to inject very often and these measurements are not compatible with that.

The wire scanner 416 (which is the only one available for profile measurements at high intensity until the wire scanners 519 are repaired) gives emittance values for the vertical plane which are inconsistent with PS and LHC measurements.

Experiments have been performed with the 25 ns beam with Q20. The setting-up in the longitudinal plane needs to be completed for intensities above nominal. Longitudinal instabilities were observed when increasing the intensity to ~1.3-14x10¹¹ p/bunch. Transverse blow-up was observed in the last train of 72 bunches injected in the SPS.

Next meeting

Monday, 22^nd October 2012 at 14:00 in room 6-R-012

Agenda:

General information (Gianluigi)

Status of space charge studies and simulations in the PS Booster (Vincenzo)

Round table (all)

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