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Agenda

  • Operations
    • Run 68: n,gamma coincidence with S101 (aka HV#4, Si HV prototype)
      • Cryogenic issues: base temperature is high and unstable, cooling power low
        • with DCRCs on base is around 45 mK. Sometimes goes into oscillatory mode to around 50 mK or runaway to around 80 mK
        • tried adding 14 mbar of 4He to mixture. Maybe some improvement but not much
      • Not sure what the problem is. Some hypotheses:
        • too little mixture
          • this is ruled out because adding mixture didn't help much. At the beginning of the run we had 726 mbar; Wednesday we measured 738 mbar (after having added 14 mbar). So we didn't lose much when the pot failed on June 7
        • too little 3He in mixture
          • this I think is also now ruled out, since we lost very little mixture this run. Last week's one-shot seemed to indicate a low ratio but I don't think the method is correct. New one-shot results
        • helium has leaked into IVC
          • we've had a small leak to the IVC at the top of the fridge. This shouldn't let much helium in except maybe during transfers. Maybe it has accumulated. Cyclical patterns and runaway warming may point to this sort of problem. On Wednesday we warmed above 4K and pumped out the IVC (which rose to a maximum of 160 nbar, not huge). We'll see if this improves things.
        • partial blockage in circulation
          • The current problems started after we started attempted LHe transfers without pre-cool (waiting for the liquid plume). This caused some violent boiling, and may have warmed up the plumbing enough to shake off some snow (this sort of thing used to happen with Little Blue). And when recovering mixture on Wednesday in one-shot mode, at one point the mixture seemed to get stuck on the condenser side even though the still-side pressure was very low.
        • 1K Pot not doing its job
          • The pot pressure has been settling to lower values than in recent runs. This suggests a low heat load, so maybe it's not efficiently cooling the returning mixture. This hypothesis is a bit unlikely since changing to one-shot mode should improve things significantly, but it doesn't.
  • Lab infrastructure
    • He-3 circulation pumps
      • still need to send back-up He-3 pump to Oerlikon/Leybold for service/repair
  • Processing and Analysis
  • Old/continuing items:
    • exploring ideas for improvements without upgrade: sidewall sources?
    • Run 62 (HV#4, Si) post-mortem: two “bad” channels seem not to be wiring problems, maybe the problem is on the detector (photos)
    • Lab infrastructure
      • plans to try to improve helium recovery
        • add length of copper tubing to recovery line, to warm helium on the way to the meter. We have used it and it seems to do something. But no indication yet that it is improving recovery.
        • maybe try to recover helium while waiting for the transfer stick to cool before hookup
      • Update on He recovery efficiency, slow transfer test
      • DAQ and data pipe
      • DAQ upgrade - discussed with Bruno about IbIs tool development
      • Data storage and backup:
        • Need to copy all Run 60 and some Run 61 data to SLAC
      • Autoprocessing and data organization development:
        • currently autoprocessing suspended, no “official” processing for Runs 60, 61, 62
        • clean up database - some info missing. Consider adding additional info
    • Possible plan to modify DCRCs (resistor swap) so we can increase front-end gain, improve IbIs (suggestion from Bruno)