Minutes of the LIS Section meeting held on 17^th November 2008

Present: G. Arduini, J. Barranco, M. Barnes, E. Benedetto, O. Berrig, C. Carli, M. Chanel, A. Franchi, S. Gilardoni, M. Martini, S. Maury, E. Métral, G. Rumolo, B. Salvant

General Information (Gianluigi)

Lauriane will leave ABP (to go back to the Prevessin departmental secretariat. Delphine Rivoiron has started to work as ABP secretary at 100 %.

The ABP group meeting will take place on Friday 28/11 from 10 to 12.

The ABP Christmas party will take place on  12/12.

The new structure has been presented to the new group leaders by Steve and the new department leaders of the accelerator sector.

Two CARE-HHH workshops are going to take place in the next two weeks. The first one is dedicated to the mitigation measures for minimizing beam-induced electron cloud build-up and will be held at CERN on 20-21/11 while the second workshop will review the status of the studies sponsored by CARE-HHH in the frame of the LHC upgrade and will be held on 24-25/11 at Best Western in Chavanne de Bogis (by invitation).

The preparation of the Chamonix meeting in Chamonix is ongoing. The workshop will be mainly devoted to the review of the lessons learned from the Sector 34 incident and to the preparation for start-up in 2009. A session will include a discussion on the LHC Commissioning with beam and on the readiness of the injectors.

Gianluigi reminded that the deadline for the submission of the abstracts for PAC09 to Oliver is the end of the week. 

Study of electron cloud build up in the MKDV1 in the SPS (G. Rumolo) - slides

The pressure spikes are visible from time to time when operating with 25 ns beam. It must be noted that the sampling of he pressure is performed in 1 second intervals while the cycle length is a multiple of 1.2 s.

For all the measurements and all the beams the bunch intensity was close (80 to 100%) of the nominal.

The simulations do not explain why the observed pressure rise is higher for 50 ns spacing. Gianluigi suggested to look at the energy deposition resulting from simulations for the 3 different bunch spacings (Giovanni verified that after the meeting but the simulation indicate once more that the maximum energy deposition is obtained for the 25 ns beam).

For the 25 ns beam a slow pressure increase is observed for the MKDH3. Gianluigi asked whether this could be explained by a lower pumping speed or conductance. After the meeting Mike Barnes sent the following e-mail.

Hello Gianluigi,

On Monday you were asking about the ionic pumps installed for the MKDH3 magnet:

The MKDH magnets have 2 pumps each; each pump is rated at 500l/s. The volume of a MKDH tank is ~0.20m^3. Thus for ~200 litres we have a total (theoretical maximum) pumping speed of 1000 l/s (theoretical minimum time-constant of ~0.2s).

By way of comparison, MKDV1 has 3 pumps; each pump is rated at 350l/s. The volume of a MKDH tank is ~0.30m^3. Thus for ~300 litres we have a total (theoretical maximum) pumping speed of 1050 l/s  (theoretical minimum time-constant of ~0.3s).

Hence based on the installed pumps the MKDH has a shorter theoretical minimum time-constant than MKDV1. However, the disclaimer is that, in each case, each pump is installed at the end of a (straight) pipe: the length of each pipe is ~49cm and the ID is approx. 16cm. Since MKDV1 has 3 such vacuum pipes (one per pump), whereas MKDH3 has only two, MKDV1 is better from this perspective.

Cheers,

Mike

There is not a clear justification for the observed phenomenon. Mike will verify whether all the pumps are working correctly.

Michel Chanel asked whether ionization of the residual gas induced by the electrons is taken into account in the simulations. Giovanni replied in the negative but in the past it was shown that this effect should not change significantly the results.

The low energy reflectivity fraction has been assumed to be 0.7 as estimated in 2004 by the benchmark of the electron cloud experiments with simulations conducted by D. Schulte. 

M. Barnes added that the MKDV1 magnet will be replaced during the shut-down. The ferrite of the magnet to be installed will be backed out and transition pieces will be fitted between the magnet and the tank

Round Table (all)

The controlled transverse emittance blow-up has been proven by Elias for different types of intermediate LHC beams. This is a tool that allows to tailor the transverse emittance of the LHC beams according to the LHC requirements whatever is the (smaller) emittance provided by the injectors. As a result of that in the future the strategy will be to require the smallest achievable emittance to the  PSB and PS and to blow it up in a controlled manner in the SPS.

 Elias is going to document the machine studies he has performed and he has started by verifying the exact strength applied to the octupoles that have been used for the blow-up. He also suggested to study the controlled emittance blow-up by simulations. Gianluigi suggested that the student working with Walter and Simone for the crystal experiments could help in that respect (After the meeting Simone verified this possibility. The student working with Walter has already completed his training at CERN).

Elias reported that no test could be performed with the IPM due to the unavailability of experts and because priority was given to solving the problems with the wire scanners in the PS-SPS complex and in testing the new electronics.

Gianluigi asked what was the conclusion of the APC concerning the wire scanners in the PS-SPS complex. The new electronics will be installed during the shut-down in the PSB and PS where tests could be performed. While the present configuration will remain for the SPS. Simone noted that for the PS and in particular for the MTE commissioning it is vital to calibrate the movement up to large amplitudes and that OASIS signals should be made available in order to verify the exact timing of the scan as required for the measurement of the LHC beam emittance.

Tests have been performed in the PS with the transverse feedback. The head-tail instability observed at the flat-bottom can be damped by the transverse feedback without coupling

Tails have been observed in the LHC beam delivered by the PSBooster. The absence of tails is an important parameter for the LHC beams.

Elias is in contact with G. Tranquille and C. Dutriat in order to verify the possibility of replacing the BSIs used for the intensity measurements in the TT20 line. Experiments conducted by Elias have shown that the intensity measurement depends on the beam position as a result of the reduction of the Secondary Electron Emission efficiency in the position where the beam is normally hitting the foil.

Simone reported that a fixed target beam with 1.4×10¹³ p could be extracted to the SPS with an extraction efficiency of ~98% (to be compared with an efficiency of less than 95% for a CT extraction). The beam had an RF structure h=16.

Simone noted that the standard BLMs installed on septum 16 are saturated and no remote reading of the LHC BLMs is available. Calibration of the beam current transformers would be also required. All that is required in order to allow tuning the extraction.

Christian mentioned that recent progress on the LINAC4 studies will be discussed at the next meeting of the working group on "PS Booster Beam Dynamics with Linac4"

Preliminary runs with ORBIT and acceleration have been performed but some more work is required to understand some observed features.

A. Adelmann has been at CERN and has discussed with Christian, Elias and Giovanni on possible parallel algorithms to be applied for space charge calculations or multi-bunch stability calculations in HEADTAIL. A possible collaboration could be set-up with L. Rivkin and A. Adelmann. Gianluigi suggested to contact E. MacIntosh to have is opinion on the solutions proposed by Adelmann before launching a collaboration. Elias will contact Andreas to discuss this.

Michel Martini is working with A. Vivoli on the IBS issues. He has also been contacted by F. Jones who has clearly evidenced a bug in ACCSIM (different results are obtained for a coasting beam when the longitudinal distribution is taken into account or the average longitudinal density while exactly the same result should be obtained. The space charge effects are overestimated in the latter case).

Christian and Masamitsu have understood the results of the simulations when an RF system is applied. The observed non-conservation of the phase space was due to the Bdot which was different from zero in the simulation.

 Next meeting

Monday, 1^st December 2008 at 10:00 in room 354-1-001

Agenda

General Information (Gianluigi)

Status of the collimation studies for PS2 (Javier)

Round Table (all)

A.O.B.

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