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105th BLM Thresholds WG meeting (IR3 studies)

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892/1-D20

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Anton Lechner (CERN), Belen Maria Salvachua Ferrando (CERN), Daniele Mirarchi (CERN), Sara Morales Vigo
105th BLMTWG meeting (IR3 studies)
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65487041774
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Sara Morales Vigo
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Participants: B.Salvachua, A.Lechner, V.Rodin, C.Hernalsteens, B.Karslen-Baeck, H.Timko, S.Morales - in person

1. Warm magnet dissipation power - Pierre Alexandre Thonet

  • Based on numbers gave by Anton - at injection and top energy
  • Current magnet of MBW same in IR3 and IR7 
  • Small difference between circuits of MQW
  • Power at injection energy in both magnets very low
  • Maximum power dissipated with present cooling settings calculated
    • Margin at injection energy -> 38kW for MBW and 44 kW for MQW
    • Margin at top energy -> 17 kW for MBW and 30kW for MQW
  • For both magnets, only coils are water cooled
    • Yokes and shielding not actively cooled
  • Thermal conduction between coils and yoke is not optimal
  • Evaluation of yoke temperature elevation during ramp -> considering a low thermal transfer between yoke and coils
    • MBW -> For 200kW 3 degrees, 4 degrees for 300kW, 7 degrees for 500kW
    • MQW -> For 200kW 1.5 degrees, 2 degrees for 300kW, 4 degrees for 500kW
    • These values do not look critical
  • Evaluation of shielding temperature elevation during ramp -> considering a low thermal transfer between coils
    • Only Cu considered
    • Pessimistic assumptions
    • For 200kW 66 degrees, 97 degrees for 300kW, 163 degrees for 500kW
  • Thermal modelling of the magnets to be done -> at injection, end of ramp and stabilized regime
    • Power evacuated by the coils
    • Temperature of each component
    • Power dissipated in the tunnel
    • Need: 
      • Map of power deposition on most critical MBW and MQW magnets -> radial and longitudinal
      • Power deposition on each component at 450 GeV and 6.8 TeV
  • Other future actions:
    • Study with EN-CV what is extra flow that could be available for these magnets
    • Install temperature monitoring on magnet components 
    • Check with EN-CV if thermal load in the tunnel is acceptable for the ventilation system
    • Is beam power loss scheme linked to integrated dose on magnet components?
      • Anton says that we are talking about short periods of losses, not continuous, the limits related to dose are still applicable 
  • Belen asks if we might be limited at 200kW at top energy (without further studies) from the shielding as we reach already 60 degrees.
    • Daniele asks if it is assumed that the power is continuous along the ramp -> Pierre says yes, Daniele says that these 200kW would be for a maximum of 20 seconds, so these values would be much lower. 
    • Belen asks Pierre to repeat values in slide 10 with only ~80 s
      • Also values in slide 9 then
    • These temperature changes are on the shielding, it is still not understood how this is transferred to the coils
  • Anton asks if there is a limit on the shielding in terms of temperature -> Pierre says there is no limit, would be ok to stay around 60 degrees 
    • Only limit in terms of temperature is at the coils
      • But no problems in any of the configurations of the coils with the numbers given by Anton
  • Pierre asks about the duration of losses at top energy
    • Losses tolerated for a maximum of 20s, reduction of a factor of 2 further than 20s
    • In that case, Pierre says that we would still have some margin
    • He asks to have a table with duration and value of losses
  • Volodymyr asks if an infrarred camera would see these differences in temperature
    • Pierre says that he thinks so, they can see if it is feasible to install it
    • Anton says that it would not be radiation hard
    • More reliable to install thermo couples

 

2. Possible MD procedure - Daniele Mirarchi

  • Demonstrate that the IR3 collimation system can sustain 200kW losses at start of ramp
  • MD approved for MD1 block -> procedure to be prepared by 13th of May
  • 3 possible methods:
    • Generate losses by scraping with IR3 primary collimators
    • Generate losses via off-momentum loss maps
    • Accumulate enough debunched beams and start ramp
  • If scraping method:
    • Need to lose around 18 INDIVs for 200kW losses
      • Max jaw speed 2 mm/s 
      • Need to scrape around 20 INDIVs to get these losses
    • Load parking limits
    • Dedicated BLM thresholds -> check loss pattern and limiting BLMs
    • To be checked if this loss pattern is representative of start-of-ramp losses
    • Is the movement fast enough to avoid BPM interlocks?
  • If off-momentum loss map method:
    • Max radial look speed ~100Hz/s 
    • Need to scrape around 20 INDIVs to get these losses
    • Interlock BPM of orbit shift
    • Interlock on RF
    • Dedicated BLM thresholds-> check loss pattern and limiting BLMs
    • To be checked if this loss pattern is representative of start-of-ramp losses
    • Is the RF shift fast enough to avoid BPM interlocks?
  • Start of ramp losses purely from debunched beam:
    • 40%/30% of debunched beam lost at peak loss rate in B1/B2
    • 44/58 number of bunches needed for B1/B2
    • Much longer program due to ramp up and ramp down
    • Only need to deploy dedicated BLM thresholds -> check loss pattern and limiting BLMs
  • Very good agreement observed between pattern at start of ramp and off-momentum loss map
  • Belen agrees that the off-momentum loss map seems to be promising, but do we know how many losses will be generated in IR7 before we get in IR3?
    • Daniele says that we need to study the loss pattern all around the ring 
    • Belen says we should scale losses from loss maps in which losses in IR7 are highest
  • Belen asks for the ADT as there are interlocks now, to be checked 
  • Anton asks if we should try to have 200kW losses for some seconds instead of only 1 s
    • Jorg says that you can change the rate of change of frequency to make it slower
    • Then we would need more bunches
    • Belen says that with more beam we would also avoid the BPM interlock
  • Time allocated still not clear 
  • Helga says we can regulate very well the blowup at injection for debunching, we should check also the start of ramp method if we have time at the end of the MD
  • Helga says that in general B1 is longer, so might be why the peak of losses is higher for B1 
    • Belen agrees it would be nice to see correlation with bunch length 
    • Helga says that for the longitudinal blowup you can target different batches
  • Belen asks about difference in cleaning inefficiency between IR3 and IR7
    • We would need to follow up for the thresholds at top energy

 

3. Simulations of off-momentum beam losses due to RF power limitations - Birk Karlsen Baeck 

  • HL-LHC bunch intensity will give bery large beam loading
    • RF voltage will be limited, but more voltage is beneficial
  • Worst case available voltage 6.2MV, 7.1MW in the best case
  • Start of ramp losses correlate with bunch length
  • Scaling bunch length with voltage
    • Does not take into account contribution with debunching 
  • Correlation of start of ramp losses with off-position beam 
  • Simple scaling with momentum spread gives a factor 2 - 3.5 needed
  • Observations during HL-LHC MDs in 2024
    • Scaling off-position beam to full beam gives a factor 1.7 above dump threshold 
  • Belen asks if we will need around 3.5 times the thresholds we will have today
    • Depends if the thresholds taken were before or after the change that was applied already 
    • Helga thinks we might need around a factor of 4, 200kW might be too low
  • Belen says that even if we allow 500kW at injection energy, we can allow less at top energy
  • Anton says it would be good to perform another test with higher power loss to verify it
  • Put all the numbers together and see if it is better to perform the MD at a higher power loss sustained for some seconds
  • Helga says we should take a factor of 4 wrt 2023 

 

AOB: IR6 thresholds - Roderik Bruce

  • Higher losses in the B1 TCSP and downstream observed in loss maps of this year during the levelling, towards the end
  • Would need to increase thresholds in Q4 and Q5 cold magnets in IR6 to reach 300kW or change collimation settings
  • Belen says we should check if for these BLMs they are aligned with collimation losses or at MF = 0.33 (for the quench limit)
  • Belen asks if this could be an effect of the orbit -> Roderik think he does not think so
  • Cleaning bottleneck in IP6, these losses should be checked 
  • Anton asks if we have 200kW so late in the cycle normally -> Not normally
  • To be checked in we risk quenching
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