23th HiLumi WP2 Task Leader Meeting
Minutes of the 23rd WP2 Task Leader Meeting held on 31/01/2014
Present: G. Arduini, V. Baglin, O. Brüning, F. Cerutti, R. De Maria, L. Esposito, M. Giovannozzi, P. Fessia, E. Métral, T. Pieloni, A. Valishev, A. Wolski, S. Weisz.
General information (Gianluigi)
R. Kersevan’s team is organizing a meeting on 5/3 to review and exchange specifications and requests having implications for the vacuum system. Gianluigi has identified two possible topics where WP2 could present the status: requirements in terms of beam clearance and electron cloud in the triplet area. Gianluigi asked the task leaders to propose possible additional topics and speakers. Action: Task Leaders.
INFN-Genova has taken over the design of the D2 magnet and they have made a first analysis. Based on that Ezio is not confident that the D2 magnets can be shortened as discussed in the brainstorming meeting organized by Massimo on 25/11/2013. Gianluigi and Massimo reminded that it is planned to review the matching section layout (including D2 correctors and Q5) by April. Feedback will be provided to Ezio at that time once all the aspects related to optics flexibility are addressed.
P. Fessia announced that D2 orbit correctors were not included in the integration studies so far, which complicates even more the integration of 4 crab cavities per beam and per side (8 in total). He also asked whether it is foreseen to have the cavities grouped in one or two cryo-modules. Oliver replied that there might be an interest to separate the cavities in two cryo-modules (e.g. to separate the function in case of the implementation of the crab-kissing scheme) but this should be discussed with WP4. Action: Paolo to contact WP4.
Next meeting will be organized on the 28/2 at 16:00 with Hermann illustrating "BBLR Project plans and needs in terms of beam dynamics studies", with the aim of getting from Hermann a list of beam dynamics questions/studies that he expects to be addressed by WP2.
Update on energy deposition studies for the Matching Section – L. Esposito
Luigi presented an update of the energy deposition studies taking into account the constraints evidenced by the integration studies performed and presented during a meeting organized by P. Fessia on 29/11/2013. In particular:
Tungsten masks have been moved away from the cold masses (1.5 m form the magnetic length) to take into account the space required for the cold-to-warm transitions and their length has been reduced to from 100 to 50 cm.
D2 aperture has been considered to be 100 mm.
TCL4 opening has been increased to 20 sigmas.
Two aperture have been considered for the Q5 magnet (70 mm – corresponding to the MQY aperture and 90 mm – corresponding to the MQYY aperture).
The results can be summarized as follows:
A factor from 3 to 4 increase in the peak power density and in the integrated dose is observed with respect the previous solution with ~2 mW/cm3 for a luminosity of 5x1034 cm-2s-1 and 40 MGy for 3000 fb-1 at the D2 magnet entrance. This might require increasing the mask thickness for D2 to reduce the radiation dose at this element. All these studies have been performed for the baseline HL-LHC optics.
From the point of view of energy deposition there is no show stopper for the installation of a MQY type magnet for Q5.
The mask in front of Q4 is not necessary, giving more space for crab cavities.
Sylvain suggested studying tolerances to misalignments of the mask (of the order of 1 mm).
Riccardo asked whether it is possible to distinguish the dependence on energy deposition of the increased distance of the mask from that on the length of the mask.
Oliver asked whether the peak power deposited depends on ß*. Luigi replied that the crossing angle is the most relevant parameter.
P. Fessia suggested investigating the possibility of installing the D2 correctors on the IP side of D2 with additional shielding to save both space in between D2 and Q4 and protect more D2 who became the weakest point.
G. Arduini replied that this possible suggestion will be added to the “desiderata” for the optimization of the layout of the matching section.
As a general comment, P. Fessia, asked WP2 if could provide the sensitivity of the required crab cavity voltage for a given beam tilting angle at the IP as a function of the crab cavity longitudinal positions. Massimo clarified, that moving D2 towards the IP would imply a larger aperture and it goes against the desiderata of magnet builders. Informations on the beam screen of D2 are still missing. Action: Ezio.
Updates from Task Leaders – O. Brüning, M. Giovannozzi, E. Métral, T. Pieloni, A. Valishev
Task 2.2 (Massimo)
Maxim Korostelev has progressed with squeeze sequence terminating the round optics squeeze and he will continue for another month on the other sets.
Task 2.3 (Massimo)
Yuri Nosochkov is studying the dynamic aperture at injection. A slight decrease of the dynamic aperture has been observed but it is not due to the new insertion element. He is investigating whether this is the result of the change of integer.
Riccardo has generated the tracking tools HL-LHCV1.0. These are now under validation.
A model for a long range beam-beam wire compensator is available in SixTrack but needs to be debugged.
An e-lens model is available in the collimation routine but not yet for long term tracking studies.
Task 2.4 (Elias)
New impedance model for the LHC and HL-LHC has been used for providing first new estimates of the single beams stability limits. This has been presented at the task 2.4 meeting on 22/1/2014 (indico.cern.ch/conferenceDisplay.py?confId=296269).
Task 2.5 (Tatiana)
Two issues were found the in the 6D beam-beam lens in SixTrack. The number of slices were limited to a maximum of 15 and the values of the beam sigmas of the slices calculated in the 6D lens were not properly calculated when the lhc=2 option (taking the beam sizes for the long-range kicks from MadX and required to estimate correctly long-range effects for flat beams) was used. The behaviour has been corrected (the max number of slices has been moved to 99) and the fixes should be incorporated in the production version of SixTrack. The tests and the content of the 6D beam-beam lens algorithm are being documented. It must be noted that for the time being the beam sizes used by the 6D beam lens are calculated partially by SixTrack using the weak beam optics and partially taken as input (e.g. calculated by the MADX mask file). This will be changed in the future. Action: Beam-beam team.
Oliver suggested generating an output file with all the input parameters used for the simulations (e.g. number of slices) so to ease debugging. This should be implemented as part of SixTrack in general. Riccardo replied that it is already the case at least for most of the input parameter, but he will check if the output is exhaustive. Action: Riccardo. (After the meeting it was checked that the number of slices is correctly reported in the output file and that a warning is being issued when a reset to 15 slices occurs.)
Task 2.6 (Oliver)
Nothing to report.
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.