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31st HiLumi WP2 Task Leader Meeting
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Europe/Zurich
6/R-018 (CERN)
Minutes of the 31th WP2 Task Leader Meeting held on 04/07/2014
Present: G. Arduini, R. De Maria, M. Giovannozzi, E. Métral (part-time), Y. Papaphilippou, H. Schmickler, A. Wolski.
Minutes, Follow-up of Actions, General Information (Gianluigi)
The Minutes of the last meeting were approved with comments from Massimo included.
Follow-up of actions:
- The criteria to be used for aperture calculations at injection are being reviewed and will be reported by R. Bruce.
Temperature effect on image current losses in the triplets (E. Métral)
Elias reminded that the LHC beam screen is obtained by co-lamination of stainless steel with a layer of Copper of 75 mm thickness to guarantee a minimum of 50 mm of pure Copper as contamination has been observed in the past during the process. The thickness is particularly relevant at low frequency (coupled bunch effects), while for high frequency only few mm are sufficient.
On a question of Hermann Elias replied that he was not sure about the thickness of aC coating considered for the estimates. He will verify that.
The estimations of the power deposition per meter has been done taking into account:
- 1 beam only.
- E = 7 TeV.
- r.m.s. bunch length = 7.5 cm.
- 50 ns beam with 1782 bunches and a bunch population of 3.5x1011 p/b.
- The Magneto-resistance (Kohler’s law).
- Power loss without and with the longitudinal weld has been computed.
The power losses per unit length have been estimated (to be confirmed) and the total loss taken into account the length of the beam screen has been evaluated but there were some doubts on the length considered. When passing from 30 K to 70 K the power loss increases by a factor of two, although the total load seems to be negligible as compared to other sources (to be confirmed).
Action Elias: to confirm the estimates for the total heat load in the beam screen of the triplet-D1-CP in range 20 to 70 K, specifying the parameters considered, considering two beams and the number of bunches given in the updated PLC table and the length of the beam screens now available in the machine drawings. The data should be summarized in a Table.
BBLR compensation test : present ideas on set-up beam conditions and measurements (Y. Papaphilippou)
Yannis mentioned that the simulations performed using BBTrack used lumped wire kick at the IP using round beam approximation. Elliptic beam should be used for the scaling. Elias noted that an approximated formula for elliptical beams (used in space charge calculations) could be used.
Plots of the ratio between kicks are provided as function of the position in Beam 1 sigma in the reference frame of the closed orbit of Beam 1. Wire multipole expansion of the wire kick is given around the weak beam orbit for analytical analysis. The multipole expansion for the beam-beam kick is more complicated but it is ready to be used in the analysis.
Effects on the orbits, tune shift and coupling are given showing that the position of the wire in the non-crossing plane is also an important free parameter for optimization. This degree of freedom is available in the present TCT/TCL collimators.
In the present machine the available collimators for wire installation in the crossing plane are one in IR1 and two in IR5.
Yannis mentioned that the installation of two wires per beam and IP (one per side) would offer the following advantages:
- Reduction of the required current (ideally halved if a position with equal beta functions in both planes is used).
- Possibility to fit better the integrated kick on either side.
- Due to optics anti-symmetry, different plane crossing and the presence of MCBX, effect of two wires in the two planes are not exactly symmetric.
- Ability to move the wire in the non-crossing plane would be desirable. This is an additional knob but at the cost of inducing some coupling.
Trains of different lengths, spacing, cogging could be used to change the experimental conditions, e.g.:
- Short trains (e.g. 12 bunches spaced by 25 ns) would avoid PACMAN effects.
- Even shorter trains (e.g. trains of 6 bunches, provided that this beam can be produced in the injectors) would limit the long range collisions to the points where the beam is round.
- If needed the effect of head on collisions could be suppressed by cogging one beam with respect to the other by 12.5 ns to avoid collisions at the IP while maintaining the number of long range collisions.
Yannis continued presenting some preliminary ideas on observables and instrumentation required. Hermann mentioned that the mechanics of all the Schottky monitors has been refurbished and one of them (1 plane, 1 beam) will be equipped with new electronics and will have the possibility to change the frequency of the demodulation for that.
SPS could be used as a test bed to validate some measurement techniques and procedures, but the diagnostics is not as complete as in the LHC.
The plans consists in consolidate simulations tools and models and evaluate predictions and scaling laws.
Gianluigi suggested to start writing a note documenting the possible measurements and beam configurations for the SPS and LHC tests so to start fixing some ideas and progress in the preparation of the tests while continuing with the analytical studies and progressing with the simulations. Action: Yannis.
Updates from Task Leaders – M. Giovannozzi
Task 2.2 (M. Giovannozzi)
A WP3 presented first results for fringe fields estimates for the triplets. First evaluation with integrated multipoles will be used for first estimates.
Next meeting will take place regularly on Friday 18th July 2014 at 16:00.
Reported by Gianluigi and Riccardo.
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