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Joint BLM Thresholds WG and Collimation WG meeting

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6/R-012 (CERN)

6/R-012

CERN
Belen Maria Salvachua Ferrando (CERN), Daniele Mirarchi (CERN), Sara Morales Vigo (CERN)
Joint BLM Thresholds WG and Collimation WG meeting
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65689083492
Host
Sara Morales Vigo
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Participants: Belen Salvachua, Roderik Bruce, Nuno Duarte, Anton Lechner, Daniele Mirarchi, Ludovica Bertolozzi, Sara Morales, Jorge Guardia, Birk Karlsen-Baeck, Dora Veres, Enrico Bravin

Power deposition from TCLD pressure spikes (TCLD.11R2 beam-gas simulations) - Nuno Duarte

  • Pressure spikes in TCLD.11R2 (installed in LS2) observed since 2022, occasionally triggering beam dumps
    • FLUKA simulations performed to evaluate risk to downstream magnets from beam-gas interactions
  • Analysis of fill #11164 --> Dumped on pressure spike by vacuum, not BLMs
    • Vacuum pressure reaching 4e-6 mbar --> ~5s with at least one gauge over threshold
    • High pressure for >140cm
    • BLMs did not dump but can see losses due to the pressure spike --> 6 BLMs on Q11R2, TCLD.11R2 and MB12R2
    • Max RS09 BLM signal used to benchmark simulations
  • Beam-gas FLUKA simulations --> Because of the low probability, inelastic interactions are forced for every primary and then normalize to pressure.
    • Location of inelastic interaction randomly sampled along particle trajectory
    • Energy deposition scored on BLMs (benchmark), MQ and MBs downstream of TCLD.11R2 (power deposition on superconducting coils)
    • Accurate model geometry around TCLD
    • Simplified gas profile in interaction region --> H2 with constant pressure
    • Scale the fluka results and then investigate the factors wrt BLM signals --> Good agreement between simulated and measured BLM signals, but fitted normalization factor is ~3.5x higher than the analytical one
    • With a gas mixture (used for FCC studies), the normalization factor is just 1.4x higher than the analytical one
  • Energy scoring from the N2 simulation (more conservative)
    • Normalized for pressure and intensity for the particular moment that is taken 
    • Energy peak happens in first dipole, but very modest (0.33 mW/cm3)
    • For simulated losses with 4e-6 mbar, the estimated maximum power density in SC coils remains well below quench limits
      • Maximum vacuum pressure before quench expected at 4e-6 mbar x 30  = 0.00012
      • Even with 1e-5mbar we will not quench
  • Daniele comments that from empirical scaling there should not be a need to increase BLM thresholds
  • Belen comments that this factor of 30 is applicable to all BLMs in the area
  • Daniele says that even increasing the maximum vacuum threshold we are well below the BLM thresholds
  • Belen asks if similar simulations for the beam pipes are foreseen, for the case of vacuum spikes in bellows for example
    • Anton says that it depends strongly on the location, and 6L2 was exchanged already
  • Daniele asks about the gas mixture composition 
    • Standard mixture used for FCC studies, for LHC it should be different compositions
      • Would it change much the simulation results?

 

Validation of updated IR3 BLM thresholds - Sara Morales Vigo

IR3 Sara —— D.M -> switch in IR7 of losses is the first fill of 75 bunches.

 

AoB: Proposal for increase of BLM threshold at TCTs during the ramp - Daniele Mirarchi

  • TCTs going to much tighter settings during the ramp this year due to the combined squeeze
    • Loss increase + threshold going down (before flattop corrections)
  • TCTPV.4R1.B2 limiting in RS11 and RS12
  • Factors needed to avoid being in warning with full machine
  • Check of power loss allowed for given thresholds 
    • TCT BLM response measured in 2025 at injection and top energy
  • Go under flattop corrections or propagate RS11 and RS12 to RS10 --> Safer to propagate RS11 and RS12 to RS10
  • Increase that we can give that is still safe
  • From EL21 -> 5 TeV
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