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Special TREX - VELO state & tests wrap-up for the LMC

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Special TREX - VELO state & tests wrap-up for the LMC
Zoom Meeting ID
68149802448
Host
Josef Sestak
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Within the link in the meeting title, you can find an INDICO used to follow-up since the incident of 10-01-2023. In case you need more information please let me know. Josef

Preliminary Minutes and outcome of the discussion 21-02-2023

  • Josef; presentation of the Phase 2 recovery.
    • Both pump-down and venting cycles did not revealed any important anomaly.
    • Safety valve SV421 tested - one actuation cycle - OK.
    • Vacuum performance of the IP8.X is expected to be close to Run 2023.
    • Detailed follow-up mandatory.
  • Q. BS - Do we expect any further mechanical cycling of the foil?
    • Load cycles are expected during: 
      • Final pump-down (+2/-5mbar).
      • Thermal cycles of the detector (simulation performed by M. Morrone).
    • Please see post discussion comment 1.
  • Bjorn; presentation of aperture analysis.
    • 1st phase analysis aimed on Injection Compatibility
      • Deformed shapes of the RF foils obtained from the simulations.
      • Previous bulging (observed during 2022) not considered.
      • Mechanical tolerance 5.5mm
      • Aperture is compatible with injection.
    • 2nd phase analysis aimed on OP feasibility with VELO blocked open.
      • Compatible with collision optics
      • VdM optics needs to be crosschecked.
    • 3rd phase analysis aimed on OP feasibility with VELO motion allowed.
      • Precise range to be defined based on aperture measurements.
  • Q. Bjorn - Are the VdMs foreseen and when?
    • JS will contact and ask LHC OP (Jorg).
  • Benoit & Christine; presentation for impedance; Pasquale for the SMOG
    • The assumptions are based on best available information, which are mostly simulations.
    • Wake-field suppressors:
      • Downstream WFS seems to be OK, partial visibility via the downstream viewport.
      • Upstream WFS  - not accessible, however the risk being effected by the incident is rather small.
      • Upstream RF contact between SMOG cell and RF foil.
        • Loosing the contact is excluded by the fact the foil does not contain lone fingers
        • Loosing the contact via loosing the mushroom engagement is unlikely.
      • Risk of mechanical interference between mushroom and storage cell.
        • Valid only for C-side half of the storage cell (fixed), A-side is floating both in radial and axial.
        • Risk of interference between mushroom and rivets of the storage cell is low
        • Risk of misaligning of the storage cell - Force of couple of kg needs to be applied to displace the fixed C-side half.
    • Q. BS - how would the possible interference constrain & affect the displacement of the RF foil?
      • This is difficult to answer and the additional assessment via simulation should be performed.
      • However the overall feeling is that this would not be a showstopper issue (statement of the LHCb).
      • JS will ask M. Morrone to prepare the study.

General discussion:

  • Q. Bjorn - Is it likely the VELO would like to move?
    • VC - Yes it is. Motion system needs to still undergo additional requalification, but if this provides reliable and repeatable result the idea would be to request to move.
  • Q. Bjorn and Benoit - When is the aperture measurement foreseen? What would be the intensity ramp-up procedure?
    • Aperture measurement should be programmed somewhere straight from beginning (OP to be asked - JS).
    • Intensity ramp-up may be different from the one foreseen as the detailed follow-up will be a must.
  • Q. Josef - What are the expected beam parameters for secondary hadronic interaction scans (done by VELO)?
    • Victor - can be done with VELO fully open, configuration depends on possibilities of using SMOG1 or not as the process requires secondary particles, so or p-p collisions or p-gas collisions.
  • Josef - wrap-up: At this stage we see no showstopper related to injection feasibility. We will follow further on, Step 1 - OK for injection; Step 2 - injection & aperture measurements with pilots at injection; Step 3 - OK for Run; Step 4 - Detailed secondary hadronic interaction scan of RF foil shape; Step 5 - Define and OK for VELO motion (with agreed range).

Post-discussion comment

  1. In-OP structural integrity failure of the RF foil (crack development)
    • Leads to lost of leak tightness between both beam vacuum and detector vacuum volumes.
    • How this can be observed? By increase of the beam vacuum pressure towards the detector vacuum pressure with an equilibrium pressure between both of these (driven by the conductance of the leak).
    • What are the risks? Higher ultimate pressure of the IP8.X, progressive saturation of the NEG in nearby sectors in 1L8 & 1R8, IT8L & IT8R would cryo-pump gas from the IP8.X (to be understood in particular case if happens), contamination of the NEG in IP8.X with gases coming from the detector.
  2. Non-mentioned risk - NEG peel-off at local buckling spots. According to Pedro Costa Pinto rather low risk to occur but may be tested if needed.  
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