Minutes of the LII Section meeting held on 20th March 2006.

Present: G. Arduini, O. Berrig, C. Carli, H. Braun, R. Bruce, M. Chanel, J. Jowett, M. Martini, S. Maury, J. Pasternak, F. Roncarolo, G. Smirnov.

Optics for LHC Commissioning and Operation with Pb Ions (J. Jowett) (slides).

The list of optics for commissioning and operation (injection, early, nominal) has been presented. These optics files are available together with the aperture files (a problem with the order of the apertures for Beam 2 has been found and fixed. G. Bellodi is recalculating the beam loss pattern with the corrected aperture model). H. Braun asked what is the reason for having a non-zero crossing angle in IR2. J. Jowett replied that it might be required by ALICE for the nominal optics in order to minimize background events. In IR1 and IR5 the crossing angles for proton physics have been taken although this is not required by the experiments. G. Arduini asked whether there is any advantage in reducing the crossing angles or in suppressing them from the point of view of the losses resulting from Bound Free Pair Production or other loss mechanisms. J. Jowett replied in the negative.

The option with b*=2 m in IR1/IR2/IR5 has not been produced yet. This might be required for early operation in 2008 if the squeeze to less than 2 m has not been commissioned by that time with protons in IR1 or IR5. Action: J. Jowett.

G. Arduini asked whether the treatment of the closed orbit distortion has been introduced in ICOSIM. H. Braun replied that the implementation will start soon. Action: H. Braun

H. Braun reminded that a possible set of realistic orbits will be needed soon. A similar approach to that used for the proton collimation studies should be followed. Action: J. Jowett

H. Braun reported that the present BLM layout does not cover fully the requirements for ion operation. S. Gilardoni has organized a meeting with B. Dehning in the afternoon to clarify the issue and to present the preliminary results on the beam loss patterns calculated by G. Bellodi and R. Bruce.

As a follow-up of the previous meeting R. Bruce has estimated the average number of MIPs per lost ion for the case corresponding to the RHIC experiment discussed last time. This number is small (0.05), the counting inefficiency of the PIN diodes resulting by event pile-up is therefore negligible.

High intensity H- charge exchange injection in the PSB at 160 MeV (M. Martini) (slides)

M. Martini has recently restarted a campaign of simulations with the program Accsym for assessing the emittance evolution of the beam at low energy in the PSB under the influence of space-charge.

A set of simulations has been performed for the CNGS beam (single batch - 1.25×1013 p/ring/pulse) with the same input parameters used in 2004 and, as expected, the results are identical to those obtained in 2004. Approximately 5 days of continuous running on a dedicated PC are required to simulate the first 1500 turns (~15 ms).

Injection is performed with RF ON (dual-harmonic h=1-2) over 67 turns, then the RF voltage is adiabatically increased from 0.62 to 8 kV. The beam coming from the Linac4 is chopped and the beam is injected at the central momentum. No longitudinal or vertical painting is performed.

After 15000 turns no asymptotic behaviour is reached in the vertical emittance. The estimated maximum tune shift (for particles at zero amplitude) is ~-0.8. The simulation are performed for a perfect machine (i.e. without magnetic errors)

A series of suggestions were made by C. Carli and M. Chanel: in particular the possibility of introducing dipolar errors to introduce a realistic integer stop band should be investigated. Action: M. Martini to verify whether it is possible to take into account dipolar or higher order magnetic errors the simulation.

C. Carli questioned also the choice (done by the Linac4 study team) of injecting with RF ON.

At the end of the discussion it was decided that C. Carli, M. Chanel and M. Martini should agree on one (two) possible alternative scenario for the simulation. Action: C. Carli, M. Chanel, M. Martini.

Round table

C. Carli, M. Chanel, J. Pasternak, F. Roncarolo: working on LEIR. Last week was almost completely lost due to a vacuum problem in the source. At present only one oven is installed. The control system is still unstable. LSA software causes now most problems.

After correction of the calibration curve of a set of quadrupoles the optics of the injection line seems now to "behave". Measurements of the response matrix seem to agree well with the expectations in the vertical plane. The horizontal dispersion needs to be measured. There is still an uncertainty in the amplitude of the energy ramp provided by the ramping cavity (factor 1.8) and in the values of the initial conditions at the exit of Linac3. To be done (Action: C. Carli, M. Chanel, F. Roncarolo):

Transmission efficiency is now ranging between 40 and 50 %. Need now to complete the commissioning of the electron cooling and of the transverse feedback: this is working in the vertical plane while one of the horizontal pick-ups does not work properly.

RF commissioning is proceeding in parallel. Preliminary vacuum studies have been conducted. The collimator system needs to be commissioned.

O. Berrig has completed the conversion of the TT2-TT10 MAD 8 model in MAD-X. He is also redefining the description of the PS magnets in the PS MAD-X model to include the circuits corresponding to the Pole Face Windings in preparation of the start-up.

Next meeting and tentative agenda

Monday, 10th April 2006 at 09:00 in room 354-1-001

General information (G. Arduini)

TT2-TT10 transfer for the CNGS beam. Study of the potential loss points. (S. Gilardoni)

Conclusions of the Beam Loss and Radiation Working Group (G. Arduini)

Status of the LEIR commissioning (C. Carli).