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95th BLM Thresholds WG Meeting (4L1, LESS, Injection)

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Anton Lechner (CERN), Belen Maria Salvachua Ferrando (CERN)
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Scientific Secretary: Sara Morales

95th BLM Thresholds WG Meeting
Zoom Meeting ID
61254635379
Host
Sara Morales Vigo
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Participants: C.Bracco (SY-ABT), Y.Dutheil (SY-ABT), C.Hernalsteens (TE-MPE), M.Himmerlich (TE-VSC), A.Lechner (SY-STI), S.Morales (SY-BI), B.Salvachua (SY-BI), J.Uythoven (TE-MPE), J.Wenninger (BE-OP), D.Wollmann (TE-MPE), C.Zamantzas (SY-BI)

Recent updates on BLM layout 4L1 and thresholds IP7 (Belen Salvachua):

  • Rise of MF from 0.4 to 0.6 for IR7 families:
    • Three dumps triggered by slow losses in RS12
    • For Run 3, master thresholds were set to collimation damage limit design specifications -> 100kW for RS12 
    • In operation, MF = 0.4, allowing 40kW for RS12 and 200kW for RS09
    • MF of IR7 families increased to 0.6 to allow 60kW for RS12 and 300kW for RS09
    • Change done on the 18th of May 2023, master thresholds unchanged -> Presented at the LMC by the Machine Coordinator at LMC#463
  • Rise of MF from 0.6 to 1 at TCP.C and TCP.B for Beam 1
    • High injection losses triggered beam dumps while injecting Beam 1
    • High signal mainly in BLMs at the TCP.C and TCP.B, while TCP.D BLM remains with lower losses -> Losses are not mainly vertical in IR7
      • C.Bracco comments that for the injection it could be that the losses are vertical. She also mentions that the ghost bunches are kicked by the MKD, which is vertical. 
    • There is a large difference between Beam 1 and Beam 2 losses
    • MF increased to 1 for TCP.C and TCP.B of Beam 1- -> Short RS set to the maximum of the electronics limit
      • Still protected for circulating beam losses thanks to redundancy in the system 
  • Temporal installation of additional IC in the 4L1 area
    • Observation of pressure spikes and losses that dump at the start of the ramp in 4L1 since 25/05/2023 -> Request to add IC detectors to monitor the area
    • Only short term solution was to replace the read-out of 3 SEM detectors with 3 IC detectors in new locations
      • Conversion factors to Gy/s for ICs and NXCALS logging of new names 
      • Concentrator (online display) publishes the previous SEM detector names
    • MF of BLMQI.03L1.B2E30_MQXA increased from 0.166 to 0.25
    • Issue identified in VMBGA.C4L1.X vacuum Module 5, exchanged and replaced -> Pressure being recovered
      • BLM detectors still being used to monitor losses in the area
    • A.Lechner comments he will upload slides from his studies. He also asks if there will be a bakeout, but B.Salvachua does not know. He also asks if there will be a revert of the MF. B.Salvachua replies that if there is not a bakeout, there could still be high losses in the area. 
  • Spontaneous discussion to discuss current strategy to change MFs. 
    • A.Lechner comments that for these changes the LMC was informed afterwards, which is ok for small changes, but for strategic changes the approval should be given beforehand. 
    • B.Salvachua comments that for MF changes also OP has access. so there should be a change in the strategy, as otherwise it is not possible to guarantee that the changes will be done before LMC approval. 
    • C.Zamantzas comments that a change in the MF is still safe, as the applied threshold values will still be conservative, so it should be allowed to make changes in the MFs without asking for previous approval.
    • B.Salvachua comments that the LMC is still informed when the changes are going to be done. 
    • J.Uythoven and D.Wollmann comment that it would be a good idea to contact directly M.Lamont and agree on a strategy for these changes. As the LMC is every two weeks, it could be blocking and an idea would be to set up a procedure to approve the changes offline. 

 

Initial discussion of BLM layout for LESS treated beam pipe IP6 (Belen Salvachua):

  • Installation of a 3-m LESS treated beam pipe for Beam 1 (outgoing beam), about 50 meters from first superconducting magnet
    • Non-treated pipe for Beam 2 (incoming beam) parallel to the Beam 1 LESS treated pipe
    • Request of 3-4 additional BLMs to monitor possible UFOs in the LESS treated beam pipe
      • BLMs included in the standard BLM data acquisition and UFO buster, but no need to interlock them
      • BLMs could be removed 2-3 years later
  • Proposal to add two extra standard IC BLMs
    • One IC BLM at the pipe location, another one downstream the LESS treated beam pipe
    • Tunnel visit to the area to be done to verify if some channels would be available to install the extra BLMs
    • AOB will be done later for the final location of the readout
    • J.Uythoven asks if it would be possible with the proposed layout to determine from which beam pipe the UFOs are coming. B.Salvachua comments that counting with the present installation plus the extra BLMs it would indeed be possible to know it. 
    • A.Lechner comments that he would like to perform some studies to optimize the position of the extra BLMs. B.Salvachua replies that there are still many things to check and the final position is not decided yet, the main problem is to determine to which channels they will be connected, and if the final position changes some meters downstream or upstream it would still be ok. 
    • D.Wollmann asks what would happen if a particulate migrates through the beam pipe closer to the superconducting magnets. A.Lechner replies that he could study it and put some numbers, but for it to be dangerous it should travel at least 10-15 meters. 
    • D.Wollmann asks about the possibility of adding diamond detectors to have bunch-by-bunch resolution of the UFO events. B.Salvachua comments that there is a diamond detector installed close to the area which could be moved, and asks the users of this detector if they are using the data, for which they reply that they are not. B.Salvachua continues saying that the possibility of moving this detector close to the LESS treated beam pipe will be assessed, but she is not sure that there will be much signal. A.Lechner comments that he can check with simulations what would be the best place to install it, possibily between the two beam pipes, close to the potential UFO source. 
    • A.Lechner asks if it would be possible to have a dedicated algorithm for the UFO buster in that location. J.Wenninger replies that it would be complicated. 

 

Injection losses: Do we need blindable BLMs? (Chiara Bracco)

  • High losses recorded during the injection process in the LHC in 2023
    • B1 very sensitive on beam parameters and configuration, B2 clean most of the times
    • Only 3 B2 dumps due to beam losses in IP7 (correlated with bad steering), while 28 dumps for B1
    • Most of times the losses are dominated by TCP.C and TCP.B on shortest running sums, however, it is not possible to conclude if losses are mainly on the horizontal or vertical plane
    • High losses recorded on TCDILs already in TI2 
      • Settings of TCDIHL.29206 readjusted to compensate for measured smaller gap
      • Losses in TI2 reduced significantly
  • Large number of parameters could impact the injection process 
    • Attempt to find correlations among these parameters, but it is not obvious to isolate a single source
      •  Main correlation between losses in TL and TCPs
    • B1 P2 losses -> Large scatter at same ppb intensity -> Non conclusive
    • B2 P8 losses -> Strong hints that blindable BLMs are not needed for 1.8E11 ppb
    • BPM data shows that steering is one of the main contributors to injection losses
      • Bunch instabilities visible in some fills, originating large losses in the ring, specially in IP2
      • Both planes affected (seems to originate in H and couple in V)
      • Observation since previous runs that uncorrectable structures appear in the lines
    • Energy offset of the SPS beams injected into the LHC fluctuating over time during a run in a band of dp/p = +- 2E-4
      • More and more evidence that changes are driven by the SPS
      • B1 and B2 always correlated
      • Offset adapted periodically
    • B1 and B2 have different extraction systems, different TL in term of optics and geometry
      • B1 TCP about 90 degrees from MSE and TCDIH.29206 on H plane
      • B2 TCPs in both planes almost 0 degrees difference wrt MSE and TCDIs
  • Improving the steering after Dp correction should allow reducing losses at collimators with high dispersion while minimizing the injection oscillations
  • Injection cleaning now setup for 200 bunches
    • Improved setup for 300 bunches could reduce losses from ghosts 
  • Monitor Factor in B1 IP7 TCPs increased and electronics limit reached
    • Do we need/can add electronic filters?
    • Do we need/can extend blindable concept to these monitors?
  • Difficult to conclude if B1 needs blindable BLMs in injection region for 1.8E11 -> Multitude of involved parameters and spread of data at fixed ppb intensity
  • B2 injection analysis seems to indicate that blindable BLMs are not needed
  • A.Lechner comments that the discussion would be different for Run 3 or HL era. 
  • B.Salvachua asks if the correction for 300 bunches instead of 200 bunches is still implemented. C.Bracco replies that it is something to implement after the TS, and there will be studies to see if it improves the situation in the long term. 
  • J.Uythoven asks about the possibility to have blindable BLMs in the TCPs from IP7. A.Lechner says that in principle it would not be possible, as there should be a redundancy in the system. D.Wollmann asks if by having blindable BLMs in IP7 TCPs we would be missing another failure scenarios. C.Bracco replies that it is something that would need to be studied. B.Salvachua comments that a problem is that in IP7 we are already at saturation, so all the RSs are underestimated. 
  • B.Salvachua also comments that the blindable system is deployed in all crates, but it would be good to envisage other approaches, like studying a different, less sensitive detector or move them to another location to avoid saturation. Another possible option would be to have a combined interlock between IC and SEM detectors. 
  • General discussion on whether to test the blindable function or removing it from all the crates directly if it is not going to be used. 
    • Should it be studied during an MD? During operational time? During commissioning?
    • General consensus that the best would be to test the blindable BLM functionality first, and removing it from all the crates if it is not needed
    • The test would not include IP7, only what the blindable BLM functionality had been foreseen for
  • Action: Discuss offline the possibility of performing such a test, including the type of request and beam parameters

 

 

 

 

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