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106th BLM Thresholds WG meeting (Limitations during operation and IR3 studies)

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Anton Lechner (CERN), Belen Maria Salvachua Ferrando (CERN), Daniele Mirarchi (CERN), Sara Morales Vigo (CERN)
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Participants: Anton, Sara, Belen, Fabian, Daniele, Natalia, Cedric, Birk, Katie, Pierre Alexandre Thonet

 

Summary of beam loss limitations for operation - Daniele Mirarchi 

  • Main limitation now -> broken hierarchy at start of ramp
    • Main correlation found -> octupole sign and strength 
    • MF raised from 0.6 to 0.8 in BLMs most limiting as a temporary measure
  • Warnings during the ramp
    • TCL.6R5.B1, TCTPV.4R8.B1
    • Warning disappear after FT corrections applied
    • At start of year, decided not to apply any changes, as it is due to e-cloud conditioning in rotated XRP and MKI
    • Ratio to dump decreasing along the year indeed
  • Warnings in stable beams
    • TCTPV.4R8.B2
      • Identified possible correlation with BLM orientation -> see talk by Belen
    • TCL.6R5.B1
      • Probably linked to e-cloud conditioning at rotated XRPs
      • To be followed up 
  • IR6 asymmetric losses
    • Higher losses due to broken hierarchy
    • TCSP becomes secondary stage of TCSG.6R7.B1 that became primary
    • B1 settings are identical to 2024
    • Less than 1 sigma larger settings than with nominal beam size, still a lot of margin

 

Findings on TCTPV.4R8.B2 BLM - Belen Salvachua

  • Observed increase signal on TCTPV.4R8.B2 BLM, nearly a factor of 2 for the same luminosity compared to previous years
    • Increase of signal was assumed to be due to physics debris
  • Investigation if increase of signal was due to intervention on BRAN 
  • Scraping data with the TCTs taken at injection during commissioning 
    • TCTPV.4R8.B2 IC BLM response higher than expected
    • LIC BLM In same location shows same increase in signal
  • An inspection was carried out in the tunnel
    • TCTPV.4R8.B2 IC BLM was oriented towards the QRL before the YETS
    • Orientation was changed after a vacuum intervention during the YETS, now placed closer to the beam line
  • Plan to make an intervention and correct the orientation of this BLM

 

Scaling of IR3 losses from operational fills - Sara Morales Vigo

  • BLM decomposition calibration at injection energy from 2025 scraping tests used to obtain proton impacts on IR3 and IR7 primary collimators at the start of the energy ramp
  • Hierarchy breakage in IR7 B1 observed at the start of the ramp, with the TCSG.6R7.B1 acting as primary and leaving a different loss pattern in the machine
    • Analysed fill 10678, where the peak of losses appears to be mainly in IR3
    • Analysed also fill 10709, where the peak of losses is shared between IR3 and IR7, for comparison
  • Scaled the BLM ratios to dump recorded at the moment of peak IR3 loss to 200kW -> Whole ring
    • Main limitations in IR3, cells 4, 5 and 6, as expected
    • BLMTI.04R2.B2E10_TCTPV.4R2.B2 and BLMTI.04L5.B1I10_TCTPV.4L5.B1 also limiting
    • Limitations found in IR6 and IR7 BLMs are expected to be linked to the operation with broken hierarchy -> not expected to limit if the nominal operation is restored
  • Daniele comments that it would be good to check if other RS are expected to saturate. This analysis will be done as well. 

 

AOB - Belen Salvachua

  • Issue with the cables that bring HV to SEM and LIC BLMs in 4L6 
    • Several cables changed during intervention, problem could not be solved
    • IC BLMs in the same positions with a different HV loop, working as expected
    • Location of the short circuit not found, expected to be further in the dump line
    • Connections there welded, will require a longer intervention
    • SEMs there in case of a catastrophic scenario with very high losses
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