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10th HiLumi WP2 Task Leader Meeting
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Europe/Zurich
6/R-018 (CERN)
Minutes of the 10th WP2 Task Leader Meeting held on 11/06/2013
Present: G. Arduini, O. Brüning, R. De Maria, S. Fartoukh, M. Giovannozzi, E. Métral, T. Pieloni, E. Todesco, A. Valishev.
Minutes of the previous meeting and follow-up of actions
The information on the RF multipoles from Maria Navarro Tapia will be provided in the next days (note after the meeting: received on 12/6/2013).
Presentation on status of weak-strong simulations: Action: Alexander, Tatiana to define the date.
The assessment of the transverse stability in the presence of and HHRF system will be addressed by end of August.
Oliver agrees with the proposal of freezing the present lattice/optics HL-LHCv1.0 and to leave other possible modification for a later version once agreed with WP3/PLC. This will be discussed at the next PLC.
D2 field quality (Ezio)
Ezio presented a first estimate of the D2 field quality based on a 105mm aperture. The field quality of the magnet is much poorer than initially expected. This is the result of the field configuration (having the same direction in the two apertures) and of the small separation of the two apertures resulting from the inter beam distance (186 mm) and large aperture (105 mm).
Ezio asked whether there is any interest in reducing the length of D2 from 10 to 7 m by going at higher field (5 T instead of 3.5 T):
Advantages:
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More space for crab cavities
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Smaller sagitta and therefore i.e. more aperture for the beam
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Possibility to move the crab cavities to higher beta
Disadvantages:
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Higher field resulting in poorer integrated field quality due to saturation
Given the poor field quality it is not wise to consider to higher fields that would further deteriorate field quality.
Margin of improvements are present but probably not enough to restore the likely needed triplet like field quality. Riccardo reminded that the aperture was originated by the compatibility with crab cavities, flat beams, the present TAN, TCT layout and for leaving margin for crab cavity voltage reduction. Stephane proposed a reduction of the aperture to 95 mm on the hypothesis that a layout without crab cavities can be re-optimized for flat beam as well as rethinking the TAN-TCT area.
Review aperture bottlenecks for the matching section elements and the associated motivations. Implication of the reduction of the aperture to 95 mm and potential mitigation measures. Action: Riccardo, Massimo
Implication of a reduction of D2 aperture on protection and mitigation measures. This should follow an assessment of the available aperture. Action: Stefano Redaelli and collimation team.
Determine the field quality of a D2 with 95 mm aperture and same inter-beam separation to quantify the dependence of the magnetic errors aperture. Action: Ezio
Determine the potential improvement with magnetic shielding. Action: Ezio.
Possible scenarios for LIU/HL-LHC upgrades (Oliver)
Oliver reported on the RLIUP review scheduled for October. For what concerns the LHC there are two scenarios: one with a bare minimum list of actions including new triplet and D1 to reach 2000 fb-1 in 2035 and the full HL-LHC upgrade including crab cavities, LR wires 800MHz RF for maximizing the performance and reaching 3000 fb-1.
Stephane asked whether there are issues for beam induced RF heating if we go to nominal bunch length of 1 ns as foreseen for the HL-LHC beam parameters. Elias replied that this is being estimated. Gianluigi noted that Elias will work in close collaboration with Rhodri Jones to assess the potential HW limitations resulting from that and possible mitigation measures. Gianluigi suggested to start collecting the expected power loss on the components that have already been studied taking into account the HL-LHC parameters. Action: Elias.
Stephane and Tatiana asked whether it makes more sense to include the beam-beam long range compensator in Scenario 1 since they make more sense in absence of crab cavities, Oliver replied that Scenario 1 is not meant to propose a stripped down version of the HL-LHC upgrade but rather evaluating the impact of a staged approach to the upgrade if needed. However LR wires are strongly supported for installation and testing.
Reported by: Gianluigi and Riccardo
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