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109th BLM Thresholds WG meeting (Recap of Ion Run and 2026 Matters)

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774/2-058 (CERN)

774/2-058

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Belen Maria Salvachua Ferrando (CERN), Daniele Mirarchi (CERN), Sara Morales Vigo (CERN)
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Participants: Roderik Bruce, Juan Esteban, Cedric Hernalsteens,  Daniele Mirachi, Sara Morales, Stefano Redaelli, , Belen Salvachua, Kate Taylor, Jorg Wenninger

Recap of Pb-ion thresholds 2025 - Belen Salvachua

  • Changes of thresholds when going from protons to Pb ions needed:
    • Use of crystal collimation in IR7 during the Ion Run-> Different loss patterns expected, different allowed power loss limits depending on whether crystals are in channelling or amorphous/volume reflection
    • MQTL Q6 sees showers from TCLA -> Needs corrections to allow operation
      • Thresholds curves set to MQM quench limits
    • DS BLM thresholds increased according to quench test results from 2015
    • TCT and TCLD thresholds reviewed in 2024 -> all TCTs in same families with same MF
      • TCLD in dedicated family that is not changed throughout the year, as the TCLD is only used during the ion run 
    • BFPP losses
  • Preliminary loss maps done in advance -> Allowed preparing thresholds during the TS -> Preferred option for the future
  • 17 IR7 BLMs distributed in 7 BLM families -> Providing simultaneous protection for channelling, amorphous and volume reflection orientations in H and V planes
  • 1st analysis of loss maps showed that the CH B2H loss map in collisions was not protected, allowing up to 120kW in CH, 30kW in AM 
    • Loss maps repeated, with B2H CH corrected, improving the cleaning
    • Daniele said that no specific setting was changed, but the results of these loss maps were not very reproducible
  • Only adjustments on TCSG_ME_ION_V_AM family, with 20% lower thresholds in accordance with loss maps
  • DS BLMs in 9 dedicated families
  • BLM thresholds usually adjusted to cope with BFPP losses and allow operation up to target luminosities, keeping ratios below 30% (warning level)
    • This year, IP8 could go beyond the target luminosity, risking to quench the Q12R8 -> Decided to avoid this, MF of this BLM reduced from .333 to 0.25, agreed to have BLM above warning levels
    • 3 BLM families with BFPP modifications
  • BLMs moved from proton to ion families with an SQL script
  • MF changed by hand with OP tools
  • Automatic scripts run to verify that the changes are correct
  • Revert after the ion run is done in a similar way
  • Work on-going to improve the procedure in LS3 -> Not easy at the moment to keep track of changes

 

  • Discussion:
    • Same strategy planned for 2026 ion run
      • Changes on BLM thresholds wrt 2025 ion run only if different settings are used
      • Stefano comments that no changes in collimator settings are planned, but no bakeout in newly installed collimator, could it affect thresholds due to the degraded vacuum? 
        • Daniele says that during other tests no significant losses were observed
        • Belen reminds that we need to revert changes due to the opening of the collimator that broke and is now replaced
      • Roderik comments that there could be possible changes on the TCT settings
        • Impact on background in IP2 and IP8
        • Daniele asks if it could be leakage from IR7 in IP8 -> Roderik says no, according to latest simulations
      • Possible reduced crossing angles
    • Daniele comments that in order to improve preliminary loss maps for BLM thresholds analysis, there could be an extra check with the BCT signal implemented in the OP tool, verifying that the change is clearly observed so that scaling of BLM signals is possible

 

Losses at injection in preparation for the High Intensity Test - Sara Morales

  • B1 injection losses in 2023 reaching the electronics limit (23 Gy/s) of the IC detectors at the primary horizontal and skew collimators
    • Estimation of protons impacting the primary collimators of around a pilot
  • Mitigation of the most limiting BLMs (3 BLMs) by installing additional BLMs in the tunnel wall (further from beam line) to reduce the BLM sensitivity
    • Resulting in a signal reduction of a factor ~10
    • Interlock functionality moved to the 3 BLMs on the wall since 2024 -> "Limiting" BLMs still present in the LHC, but not interlocked
  • Agreement with OP to assume 1e11 lost protons in one turn as maximum tolerable limit of injection losses
    • Could be achieved with a combination of IC and LIC detectors mounted on the tunnel wall -> Study on-going to assess BLMs that need to be "moved", installation planned for LS3
  • MD in September 2025 with injection of HL-LHC trains
    • Fills 11016, 11017 and 11018
    • Injections of 287/288 bunch trains with 2% SPS scraping analyzed
  • For B1 injections, BLMs with values above the warning level (30%) found in IP2 and IP7
    • IP2: Q6L2 up to 73%, Q8L2 up to 61% appearing for most injections above 30% up to RS09 -> BLMs with filters!
    • IP7: TCP.D6L7.B1 up to 55%, TCSG.A4R7.B2 up to 35%, TCSPM.B4R7.B2 up to 31%, not in every injection, BLMs not on wall 
  • For B2 injections, BLMs with values above the warning level (30%) found in IP8 and IP7
    • IP8: Q6R8 up to 61%, Q8R8 up to 34% appearing for most injections above 30% up to RS02 -> BLMs with no filters!
    • IP7: TCP.D6R7.B2 up to 32%, TCP.C6R7.B2 up to 59%, TCP.B6R7.B2 up to 42% appearing for most injections, BLMs not on wall
  • 2023 B1 injection losses not reproduced during the 2025 HL-LHC MD
  • BLMs on the wall not limiting
    • Main limitation moved to BLMs in injection areas -> Showers from TL collimators, not direct impacts on devices -> Use the blinding functionality?
  • Plan to commission the blinding functionality of BLMs in IP2 and IP8 in 2026 with ABT colleagues
    • First part of commissioning during TL setup
    • Second part during scrubbing period
  • Should the filters on BLMs that might use the blinding functionality be removed?
  • Check list of BLMs that could use the blinding

 

2026 main topics - Belen Salvachua

  • Update of IR3 BLM thresholds to allow higher off-momentum losses at start of the ramp
    • Currently limited to 60kW in B2 
    • Best way to modify these thresholds would be to implement a model similar to the one in IR7, with BLM response and allowed power loss
    • Daniele asks if we could just apply the same corrections as in the MD for operation this year, and prepare the model later during LS3
      • Belen comments that it is preferable to implement the model now
  • Preparation for HI test
    • Pressure spikes at TCLD -> Possible adjustment of BLM thresholds to quench level of downstream Q11 magnet from this loss scenario
      • Review loss patterns on both sides and see margin there 
    • Elliptical interconnecting vacuum modules in LSS1/5
    • Loss maps needed at 3 TeV to verify if flattop corrections are needed in IR7
      • Loss maps done last year, could verify from there
  • Injection losses
    • Commissioning of blindable functionality with ABT
    • Study BLMs to be installed on the wall during LS3
  • Ion Run -> Discussed in previous presentation
  • Update of TCT thresholds for protons, with new model
  • Thresholds management -> Being followed up with colleagues from OP
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