Minutes of the 22st WP2 Task Leader Meeting held on 06/12/2013
Present: G. Arduini, O. Brüning, R. De Maria, M. Giovannozzi, E. Métral, T. Pieloni, R. Tomás, A. Valishev, A. Wolski
General information (Gianluigi, Oliver)
Giorgio Ambrosio will take over from Gianluca Sabbi in the role of LARP Manager for the Magnet effort from 1/1/2014.
The Crab Cavity Workshop (CC3) will take place on 9-10 December 2013.
The energy deposition studies have identified a solution requiring the installation of tungsten masks in front of D2, Q4, Q5 and Q6 and TCL collimators in front of D2, Q5 and Q6. Integration issues have been identified. New studies will be performed taking into account the integration constraints, furthermore the simulation so far have been done with a 90 mm aperture Q5 (corresponding to an MQYY magnet aperture) and compared with a 70 mm aperture Q5 (corresponding to an MQY design).
Last PLC (3/12/2013):
Review of the IR4 installation;
Status of the HL-LHCv1.0 optics;
New baseline with 4 crab-cavities per IP side;
D1 length reduction has been approved;
A revised version of the tolerances used in the n1 definition has been presented, taking into account the Run I LHC experience. Further reduction in tolerances is expected to be obtained with the installation of collimators equipped with BPMs but this will have to be confirmed in 2015 when experience with this type of collimators will be gained and Machine Studies will be performed to assess the level of correctability of the beta-beating for the ATS optics. For the time being it is assumed that 12 beam sigmas (*=3.5 m) can be protected by the collimation system in the HL-LHC era.
A deliverable report for the injection parameters is being written.
Possible upgrade schemes with a 200 MHz system – R. Tomás
Rogelio presented the possible beam parameters and performance with a 400MHz and 200 MHz RF systems. The 200 MHz system offers the possibility to inject longer bunches in the LHC and therefore larger longitudinal emittance. This allows increasing the bunch population from the SPS at constant longitudinal brightness which is the major limitation in the SPS even after the upgrade. A maximum RF 200 MHz voltage of 6 MV, instead of 3MV initially considered, would allow using the 400MHz RF system as second harmonic system in bunch lengthening or shortening mode and would allow recapturing the beam on the 400 MHz RF system towards the end of the fill and use the bunch length as a levelling tool.
The heat load due to electron cloud is affected mainly by the bunch length and not bunch intensity and for that reason a significant reduction is expected for the considered scenario. The power loss from impedance decreases considerably with longer bunches.
A crab cavity at 400MHz can only affect the core of the bunch, but it creates distortions in the transverse position along the bunch. Scenarios with 200MHz RF system with and without crab cavities have been considered and their performance evaluated. The option of crab cavities operating at lower frequencies (400MHz, 320MHz, 200MHz) has been considered too as a tool to minimize the peak pile-up density. Integrated luminosities and pile-up densities comparable to those obtained with 400/800 MHz systems and 400 MHz crab cavities with crab kissing scheme can be obtained with 200/400 MHz system and 200 MHz crab cavities but without needing cab kissing. This can be obtained at reduced heat load due to electron cloud and impedance. Rogelio noted that the lower Qs obtained with a 200 MHz system could be an issues because of the expected lower TMCI threshold (2.6×1011 p/bunch as compared to 3.4×1011 p/bunch with nominal parameters).
Oliver asked whether the RF-curvature in the case of crab cavities at 400 MHz has a detrimental effect for beam-beam. Rogelio and Sasha replied that beam-beam effect should be dominated by jitter.
Updates from Task Leaders – O. Brüning, M. Giovannozzi, E. Métral, A. Valishev
Massimo reported that the SLAC team has started a tracking campaign at injection with the SLHCV3.1b optics. A new error table for D2 is expected from WP3 taking into account the recent developments. Mask files for tracking with HLLLHC1.0 are under preparation as well as a general tool for 11T dipoles installations in the dispersion suppressors to evaluate the impact of the magnetic errors on the dynamic aperture at injection and in particular for the ATS optics in collision.
A Task 2.3 meeting will take place on 16/12 to give a status on the tracking tools for crab cavities and fringe field simulations. The effect of the triplet power converter ripple on the tune ripple is being studied by Myriam and Stephane and an alternative scenario for the powering is being considered to reduce the impact of the ripple.
After reminding the recent and future milestones and deadlines, Elias reported briefly the outcome of the LHC Performance Limitation review held at the end of September. He concluded that the interplay between several effects (impedance, damper, beam-beam, e-cloud, etc.) needs to be further studied. The conclusions and the next steps are being written by Elias and should be issued before Christmas.
The impedance model as it stands now will be frozen and published to be used for studying intensity limitations. In parallel work will continue to update the impedance model including an evaluation of the uncertainties expected.
Sasha reported that the verification of the implementation of the 6D lens in SIXTRACK is progressing and a follow-up meeting will take place on 11/12 to review the status. A note has been issued to illustrate a possible use of an electron lens as a long range beam-beam compensator.
Sasha also reported that Sergei Nagaitsev will take over the leadership of the Accelerator Division at FermiLab from Roger Dixon and Hasan Padamsee will take over the leadership of the Technical Division form Giorgio Apollinari
Oliver reported that an update of the number of bunches would be needed in the official parameter list. Gianluigi replied that this is being compiled as part of the Deliverable Report 1.3 on the “Beam Parameters at LHC Injection”.
Gianluigi reported that the collection of the intensity limitations is being carried out by Rhodri. In particular he should follow-up the heat load expected in the IP2/8 triplets and possible cryogenics limitations in collaboration with Task 2.4 and WP9.
The next task leader meeting will take place on 31th January and it will be dedicated to an update of the energy deposition studies in the matching section and the usual task leaders’ update.
Future topics will be:
Status of crab cavity development and present specifications
Plans for the beam-beam compensator and required input from WP2.
Reported by Gianluigi and Riccardo.