Participants: C.Hernalsteens, A.Lechner, S.Morales (remote), V.Rodin, B.Salvachua, J.Wenninger

• BLM thresholds in IR3 - Belen Salvachua
  • The BLM thresholds in IR3 were reviewed in 2012
    • Documented in LHC-BLM-ECR-0034 - "Increase of BLM thresholds for collimators in IP3"
    • Study presented in BLM Thresholds Working group 11/07/2012 - "BLM dump thresholds for off-momentum losses in IP3"
  • Collimation thresholds in IR3 still based on these values
    • Master thresholds allowing for a power loss of 500kW anywhere in the machine
    • MF currently set at 0.4, allowing for 200kW
    • Sharing between IR3 and IR7 was not well know at the time
  • For the Q6, there is no difference between IR3 and IR7 threshold at injection energy

    • Only difference would be the flattop corrections applied at top energy in IR7 Q6 thresholds

  • Most limiting BLM in IR3 at the start of the energy ramp is BLMQI.06L3.B2E10_MQTL, in family THRI.IP3.P1_MQTL (Q6 family), with MF=0.4
  • What is the designed power loss allowed locally in point 3?
    • • To be assessed 
      • Contact collimation

• Power loss at the start of the energy ramp - Sharing between IR3 and IR7 - Sara Morales
  • Power loss at the start of the energy ramp calculated from the BLM loss plane decomposition calibration
    • Calibration performed using the scraping data from 03/05/2024 at injection energy
    • Scraping performed on all primary collimators in IR3 (off-momentum) and IR7 (vertical, horizontal, skew) -> Considered independent beam loss scenarios
    • Scraping performed on single jaws to observe differences in BLM response
    • Proton impacts on left and right jaws of the primary collimators in IR3 considered as independent scenarios for the first time
  • Calibration applied to the start of the energy ramp for E<500GeV for all fills with more than 10¹² protons per beam (MDs excluded)
    • RS09 used (~1.3s integration time) 
    • Total lost intensity in each start of energy ramp typically around 10¹² protons for full intensity, in good agreement with the BCTDC
    • Minimum beam lifetime well above 0.006h and peak power loss well below 200kW in all cases
    • Peak power loss around 10 times higher in IR3 wrt IR7 for both beams
    • Accumulated power loss during the start of the energy ramp in IR3 similar for both beams
    • Higher accumulated power loss for B1 in IR7 - mostly vertical losses that appear after the main loss peaks
    • For B1 -> Main impacts on the internal (right) jaw of the IR3 primary collimator, vertical IR7 losses afterwards observed in some fills
    • For B2 -> Main impacts on the internal (left) jaw of the IR3 primary collimator, but a first peak corresponding to vertical IR7 losses and a later peak corresponding to impacts on the external (right) jaw of the IR3 primary collimator are observed
  • Main limitation is for the RS10 (~5.2s integration time) of the BLMQI.06L3.B2E10_MQTL, which has reached at some point even 80% of the threshold
    • Calibration with RS10 applied to the start of the energy ramp for E<500GeV for all fills from the 15th of May with more than 10¹² protons per beam (MDs excluded)
      • Signal to dump ratio of BLMQI.06R3.B1I10_MQTL and BLMQI.06L3.B2E10_MQTL show correlation with losses in B1 and B2 IR3 primary collimators, respectively
      • BLMQI.06R3.B1I10_MQTL is expected to dump at a power loss in B1 IR3 primary collimator of around 50kW sustained for ~5s
      • BLMQI.06L3.B2E10_MQTL is expected to dump at a power loss in B2 IR3 primary collimator of around 20kW sustained for ~5s
      • Anton and Volodymyr confirm that they also observe in their simulations a higher energy deposition in the concerned B2 element in comparison with the equivalent B1 one

  • It would be needed to assess the energy deposition locally in Q6 with simulations

  • Would it be possible to raise the threshold of the BLMQI.06L3.B2E10_MQTL temporarily (as it would be dumping at a very low power loss, unlikely to quench a magnet or cause damage) before a full study of the energy deposition in IR3 is performed?
    • Main loss scenario in the THRI.IP3.P1_MQTL is an orbit bump

       

       

• FLUKA BLM benchmarks in IR3 and expected power deposition - Volodymyr Rodin

  • Estimation of the most limiting elements in the off-momentum cleaning section to understand where BLM thresholds can be relaxed
  • FLUKA model of IR3 constructed with LineBuilder using optics and collimator gaps provided by Natalia Triantafyllou
    • Includes latest shielding updates in the MQWs from LS2 
  • Initial impact conditions calculated from the optics and bunch parameters
  • Impact depth was scanned
  • Simulation results benchmarked with BLM signals from fills:
    • 8735 in 2023, losses in B2 lead to a dump
    • 9670 in 2024, main losses in B1 but no dump
    • Simulations performed with 2024 optics for B1 only with various impact conditions
    • Signal from the two beams to include crosstalk considered including weights
    • Very good agreement between simulation and BLM data
  • Analysis consistent with Sara Morales' results
  • Power deposition computed in elements with most limiting BLMs for both analyzed fills
    • Power deposition at which the elements would be dumping at RS09 and RS10 (most limiting RSs) included
    • BLMQI.06L3.B2E10_MQTL most limiting, would be dumping at a power deposition of 0.005kW for RS09 and 0.00184kW for RS10 on the element, 32 kW for RS09 on the B2 IR3 primary collimator
    • Next limiting element (TCLA.A5L3.B2) would be dumping at a power deposition of 0.67kW for RS09 and RS10, 85kW for RS09 on the B2 IR3 primary collimator
    • Extensive analysis in different IR3 elements, consistent level of allowed losses 
  • Anton comments that if we double the MF for the BLMs at the Q6, the next element would still be dumping at a higher energy deposition
    • He also comments that the allowed power loss at each element is much lower compared to what is allowed in IR7
  • Belen comments that if for the Q6 family the RS10 is set to be equal to RS09, we would get about a factor of 2 margin in RS10
    • If this correction can be applied only at injection energy, this would avoid having higher thresholds also at top energy
    • Could be a temporary solution until more studies are done on the Q6 energy deposition and power leakage to the DS
  • It is still needed to review the thresholds for the collimators in the IR3 LSS
    • Belen suggest doing a pseudo "quench test" in IR3, going to 50kW or 100kW power loss at injection energy to see if we do not quench, to have confidence that it is possible to raise the thresholds
    • It would be needed to study the actual limits for power loss in IR3, considering also the risk of quenching at top energy
    • IR3 has much worse cleaning efficiency than IR7
  • Belen comments that there is probably enough data from beam scraping to assess the leakage to the DS
  • She also comments that for a similar study to what was done in IR7 it would be good to check if the BLMs are in the same relative positions at the magnets
    • It could be possible to relocate them if it is not the case

   

   

• Summary of actions on IR3 thresholds:
  • Q6 IR3 thresholds:
    • Set RS10 to RS09 only at injection energy to gain a margin of around 2 in allowed power losses 
    • Write ECR to document changes
  • Continue dedicated energy deposition studies in the IR3 Q6 magnets
  • Check power leaking to the DS
    • Assess possibility of gathering this data from the already performed beam scraping at injection energy
  • Review thresholds for collimators in IR3 LSS
    • Check positions of BLMs and possibility to relocate them
    • Think of requesting beam time for a pseudo "quench test" to verify allowed power losses before quenching

• BLM thresholds for physics debris - Belen Salvachua

• • • This limits the maximum luminosity for ATLAS to go to mu ~65-66 (as the lump server inhibits steps if any RS is in warning in the IR)

    • This year the target mu is of around 66

• • Actions: 
    • Study the needed correction so that it does not appear in warning for the requested luminosity and apply it to the THRI.IP15.P3_MQXA_FT family
    • Write ECR to document changes

• AOB: 
  • Belen asks Jorg to provide in August either at a BLMTWG or LBOC meeting the requirements from operations regarding injection limitations in BLMs

  • She also recalls that in the following months it is needed to prepare the Ion Run

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    Jorg comments that he prepared a list with the BLMs that need to change MF for the aligment of the XRPs called "BLM XRP aligment"

     

    • Belen and Anton wonder if this change in the MF for the alignment of the XRPs is really needed...