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16th HiLumi WP2 Task Leader Meeting
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Europe/Zurich
6/R-018 (CERN)
Minutes of the 16th WP2 Task Leader Meeting held on 13/09/2013
Present: G. Arduini, R. Bruce, R. De Maria, M. Giovannozzi, E. Métral, T. Pieloni, B. Salvant, A. Valishev, A. Wolski
Minutes of the last meeting and follow-up of actions
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The minutes have been approved without changes
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Actions:
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Gianluigi and Riccardo: The tables with LIU beam parameters provided by G. Rumolo and the tables of the proposed scenarios are going to be distributed on Monday 16/9 at the latest (Done).
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Riccardo and Miriam confirmed that the flat optics with 40/10 cm requires a stronger Q5 in point 6 and an additional sextupole in Q10. This is not required for the 40/20 cm optics.
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Scaling of beam induced RF heating for HL-LHC – B. Salvant
Benoit provided an update on the beam induced power deposition due to impedance. Gaussian distributions with a bunch length of 7.5 cm r.m.s. have been considered so far. Benoit asked whether this is a realistic assumption. Gianluigi replied that bunch flattening with the 800 MHz is being considered for IBS blow-up reduction and for increasing the luminous region size in combination with crab kissing. Action: Benoit to contact Elena Shaposhnikova and Stephane Fartoukh to get estimates of the parameters that they are considering.
The knowledge of the distribution is particularly important for objects showing narrow band structures although most of the items have a broad band.
Benoit presented the expected scaling and he reviewed particularly the objects that showed problems in 2011/2012. Most of them were related to non-conformities.
The power deposited by image currents in each arc beam screen is 0.53 W/m corresponding to approximately 53 W/half-cell. 200 W/half-cell are available for cooling (synchrotron radiation and electron cloud power deposition should be added).
Gianluigi reminded that the effect of the simultaneous presence of the two beams on heat load in the triplet should be estimated (see Action during 11th WP2 Task Leader meeting). Benoit replied that Giovanni will include this in his presentation on the heat load on the triplets beam screens due to electron cloud. Action: Elias.
For the TCTs the heat load is about 500W for a designed 25kW cooling power, but the heating being asymmetric may lead to mechanical deformations. Gianluigi mentioned that the available cooling power may not be sufficient for localized sources where there is no good conductivity. Massimo suggested testing with measurements and simulations the cooling effectiveness. Action Elias to discuss the equipment teams about this possibility. Roderik noted that power deposition in the collimators is dominated by beam losses on the jaw. For TCTP ferrites are going to be installed to damp trapped modes. Ferrite outgassing could become an issue if the thermal contact of the ferrites with the tank is not guaranteed. Other options are being considered.
TDI is being refurbished during LS1 and new design should be foreseen for after LS2. Coating of the jaws is mandatory and TDI should be open as soon as possible once injection is completed. Gianluigi asked to evaluate the scaling of the trapped modes too although these should be less than 1 kW for close collimators at HL-LHC nominal parameters. Action: Elias to provide estimates including the trapped mode analysis. The cooling effectiveness is not still assessed. Action: Elias to ask for more accurate analysis of heat management.
Injection kickers (MKI): all the kickers ceramic vacuum chambers are going to be equipped with 24 conducting strips (they were 15 in 2012) during LS1. This upgrade might not be sufficient for the HL-LHC nominal parameters although the estimate has been done in the most pessimistic scenario. Gianluigi and Massimo noted that the data collected with the kickers with the different number of stripes (15 for most of the kickers in 2012, one kicker with 19 strips and all the kickers with 24 strips in 2015) can be used for benchmarking with the available temperature data. Action: Impedance team to analyze the temperature data collected in 2012.
A first estimate of the heat load on the strip-line pick-ups for the present triplet has been provided and amounts to more than 55 W. This is installed in a cryogenic environment. An estimation of the heat load with the larger aperture strip-lines for the new HL-LHC triplet should be sent to Laurent Tavian. Action: Elias to transmit the information concerning the heat load on the striplines for the HL-LHC triplet.
A new design of the BSRT is ongoing to reduce RF heating. The new design should be checked against the HL-LHC parameters. Action: Impedance team
Gianluigi asked to create a table with the expected heat loads for all the LHC components for which the impedance is known assuming the HL-LHC nominal beam parameters. Action: Impedance team.
The RF heating for the various upgrade scenarios that will be circulated should be estimated highlighting the need possible interventions on some of the hardware components. Action: Impedance team.
Update on aperture margin estimation for HL-LHC - R. Bruce
Roderik gave an overview of the collimator settings in sigmas (assuming 3.5 m emittance) assumed for the design report, for the operation in 2011 and 2012 and those expected for HL-LHC operation based on the experience gained in 2012. Orbit errors and tolerances prevent a simple scaling of the collimation settings with the beam size; furthermore impedance can set a minimum limit in collimator opening in mm.
The main differences of the collimator settings used in 2012 with respect to the nominal settings is in the retraction of the TCS (secondary collimators) in IR7 with respect to the TCP in IR7 (primaries) (2 instead of 1 sigma retraction) and in the retraction of the TCTs in IR1/5 with respect to the TCDQ in point 6 (1.5 instead of 0.3 sigmas). The retraction of the TCS with respect to the TCP in IR7 can be likely reduced thanks to the implementation of the button BPMs in the collimators but the exact gain can be evaluated only after operational experience with them. The same applies for the retraction of the TCT in IR1/5 with respect to the TCDQ.
Roderik then reviewed the estimates of the aperture based on n1 with the tolerances defined for the LHC design and those assuming beat-beating (10% to be compared with 20% for the LHC design) and orbit errors (1 mm peak to be compared with 4 mm for the LHC design) and assuming the same alignment and mechanical tolerances. The measured aperture is compatible with the less conservative tolerances
After discussion it was decided to use the latter definition of n1 and to spell out the implications of that in terms of mechanical tolerances and alignment that have been achieved in the LHC construction so to make sure that the same excellent conditions are obtained for HL-LHC. A table specifying the new definition and the corresponding requirements in terms of mechanical and alignment tolerances (based on the achieved values) should be provided. Action: Massimo, Stefano and LCU team.
Riccardo asked how the dispersion effects can be taken into account, Roderik replied that these could be taken into account by considering the maximum RF excursion that is presently allowed by interlocks.
Roderik used the new n1 method and consideration for collimation to benchmark the PIC scenarios, showing that the 20/40 beta is between reach.
Sasha asked whether the retractions among collimators could be decreased with intensity. Roderik replied that the scaling rule is not evident.
Gianluigi asked all task leaders and teams to review critically the proposed upgrade scenarios and their assumptions. Actions: all task leaders
Reported by Gianluigi and Riccardo.
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