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Status and next steps for the FCC-hh Interaction Region design
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Europe/Zurich
6/R-012 - conference room (CERN)
Present: Angeles, Maria, Ilaria, Xavier, Ezio, Francesco, Roman
Two groups in CNRS (LAL, IPNO) and CEA. and UK (Oxford) To be included in future meetings.
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MAGNETS
Ezio and Miko present a new iteration. No grading yet considered. Mikko will not contribute further to this.
The dipoles would need more aperture than shown in the table, almost a factor 2. Ezio guesses that 80mm should be considered as a maximum. To be iterated in the email since reducing the field helps with the aperture.
Roman asks about having 2 MQX different models? Ezio replies that it is not ideal but can be studied and optimized.
Francesco asked about margins. Ezio recommends 20% margin while community recommends 10%.
40mWatt/mm should be kept in mind.
Francesco also asks about the new layout with larger L* and aperture. Ezio replies that this possibility is on the table.
-> Grading could give 5-10% extra field.
-> What to do with radiation? We should consider new materials to resist as much as metals which is in the pipeline. Critical for the upgrade performance.
-> Other technologies?
-> Field quality? In about 1 month Ezio can present field quality results about field quality.
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Beam-beam limits, Xavier
Predicts a minimum useful beta* of 0.06m (round).
Without crab cavity beta* below 0.3m is not interesting unless one is limited by head-on beam-beam tuneshift (else yes). Nevertheless it also helps for the fill length.
Beta* leveling (above 0.3m) can give 50% more luminosity with long fills.
Beta* leveling is very helpful if tune shfit is not a limit.
Adding a crab cavity and small beta* (~0.2) can boost performance but only if beam-beam tune shift can reach 0.03. Maybe beta*=0.2m should be the target. Lower beta*s than 0.2m give very little improvement.
Crossing scheme. W. Riegler presented spectrometers at 10-20m close to the IP, similar to dipole first configuration. Options to reduce or increase long-range encounters are presented. This affects energy deposition, aperture and beta* reach. To be followed up with W. Riegler.
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Optics options, Roman
Two options so far, L*=36m and 61m.
With analytical scalings the longer L* the lower beta* reach. The longer the triplet the lower beta*. On the upper bound of L* are DA, chromaticity and required length for IR.
Pion tracking code under development.
Angeles asks about the "split Q1" option. Roman answers that this might mitigate radiation dose.
Barbara asks about how to proceed with arc and DA tasks. Roman suggests that an efficient gluing of IR optics and arc is needed as this would be an iterative process. Antoine Chance is the responsible of this, to be discussed.
Barbara also asks about injection optics. Also to be looked up.
Material of the shielding? Tungsten.
Francesco comments about the pion code and the fact that the strength and aperture have to be considered.
Roman runs first MADX to provide inputs to the pion code.
Xavier comments about using MADX, to be explored or compared.
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Energy deposition, Francesco
Operational condition: regular swaps of crossing angle sign to distribute losses. Or even crossing plane.
Ilaria is currently quantifying this for LHC considering only sign change. Lumi could increase by ~60% for HL-LHC parameters rough guess.
To reach the upgrade parameters the new materials 5x more resistent are required.
New triplet proposals should come soon.
Roman asks about new material of shielding. Tungsten is OK, Uranium would be better.
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Collimation, Maria
N1 review for LHC. However for HL-LHC N1 is abandoned and sigma_n is used.
In FCC the cryo-collimators can be considered from the beginning.
Taking HL_LHC baseline FCC-hh needs 15.5 sigmas aperture clearance for optics design.
Angeles will propose a combined transverse and energy collimation system.
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