Minutes of the 33^rd WP2 Task Leader Meeting held on 05/09/2014

Present: G. Arduini, O. Brüning, R. De Maria, P. Fessia, M. Giovannozzi, R. Kersevan, E. Métral, Y. Papaphilippou, E. Todesco.

Minutes, Follow-up of Actions, General Information (Gianluigi)

The minutes have been approved with comments from Massimo (as suggested by Stephane): ripple studies will be performed also with a larger tune spread as a result of crab cavities kicks in IR1-5.

A meeting with Ezio, Amalia, Jean-Paul will be organized to discuss power converter choices by taking into account range and duration of the operating cycles.

Follow-up and new actions:

• Riccardo sent an email WP leaders and WP2 task leaders to communicate the address of layout and optics repositories (i.e. task 2.2 webpage, summary excel file, optics website, AFS directory). Riccardo added that had been already in touch with Paolo, Luigi, Rhodri and Vincent to exchange position, length, apertures of the HL-LHCV1.1 layout.
• E. Todesco was asked to provide information concerning the expected spread of transfer function error for the new HL magnets in particular triplets for the forthcoming meeting with Amalia and Jean-Paul. Action: Ezio.
• Oliver proposed to review the impedance estimates for crab-cavities before the next collaboration meeting since in the last collaboration meeting critical values have been shown by Benoit from first estimates. Action: Elias.

PACMAN effects for the HL-LHC nominal scenario (orbit, tune, chromaticity) T. Pieloni

The talk has been postponed to next meeting (19/9) due to the unavailability of the speaker.

Temperature effects on image current losses in the triplets, part II (E. Metral)

Elias reported an update of the power loss due to image currents in the triplets and MS magnets in IR1-IR5. Input data and equations have been shown by highlighting the dependence of copper resistivity on temperature and magnetic field and a new equation that takes into account the presence of the two counter-rotating beams in the common chamber for the triplets and D1. Results have been reported in W/m for each class of magnets for 25 and 50 ns beams (worst case scenario). The two beam effects can be approximated as taking twice the estimates from the single beam formula. In reply to Paolo questions, Gianluigi replied that quantities per cryostat should be taken by multiplying the linear power density on the main element and multiply by the length of the assembly: marginally higher values of total power loss will be obtained.

Oliver proposed to look at the estimated losses for Q7 against the present cooling power as the item will not be upgraded and need to be consistent. This is due to the fact that the value of the current for 50ns has been estimated few years ago as the largest possible compatible with the LHC beam screen cooling capacity (limited by the size of the capillaries) and the evaluation should be reviewed by taking into account new information. Action: Elias will provide the estimates of the heat load to the beam screen due to image currents. He will also check the available cooling power in the arcs with the Cryogenics colleagues.

Updates from Task Leaders (Task leaders)

• Task 2.2: Massimo asked Roberto if any update on the beam screen models will be soon available both for the triplets (Roberto replied that a talk from Cedric is ready to be given for the HL-TC) and the matching sections
• Task 2.3: Tracking simulations are on-going with HL-LHCV1.0. A report could be given. Check with beam-beam should be repeated with the same optics version. Action: Sasha, Tatiana to verify the effects of the various multipoles.
• Task 2.4 – 2.5: Elias reported that studies on stability diagrams and octupole effects as well as estimates for instabilities taking into account coherent beam-beam modes and impedance are being carried out. A talk by Javier on Beam-Beam simulation has been presented at the HSC showing confidence on the beam-beam models for tracking. Riccardo commented (and confirmed after the meeting) that the agreed changes on the code have not been implemented yet. Action: Tatiana.
• Task 2.7: Elias has taken over from Rhodri the leadership of this Task.

Next meeting will take place on Friday 19^th September 2014 at 16:00.

Reported by Gianluigi and Riccardo.