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Teleconference link: https://umn.zoom.us/j/8797896096 or https://umn.zoom.us/my/fritts
Access code: 879-789-6096

Agenda

  • Run 72 in progress
    • Payload:
      • Housing in Position 1 with Source mover, LEDs, thermometer and a test screw-terminal for NbTi
        • Heatsinking added to motor coil solder joints
      • G101D with Side 2 etched, Position 2. Source pointed at readout side.
        • One QET wired with twisted pair instead of side coax
      • External electrode in Position 3
    • Side1pE not working, appears to be open. Possibly a wirebond broke.
    • Fridge basically working, base around 51-56 mK.
      • 1K Pot running warmer than normal, makes base temperature sensitive to LN2 Cold Trap bath fills, which is annoying
      • We've increased the Still heater power twice, keeping the base low. But each time the Circulation pressures go up. It may be getting slowly worse
      • Assuming that the 1K Pot was not sufficiently purged or has a bad o-ring, should be able to fix this in next cooldown
    • Fridge shield built (lead on all 4 sides). This makes the Am lines much easier to see.
    • Taking and analyzing data at various drifted biases
      • Yesterday's -250V data shows an even lower Luke gain, implying an effective bias of 24.5 V, which is 16.5% of what we expect with a 1mm gap
      • Apparent Luke Gain implies much lower biases than calculated. Example: +250V data, Luke gain implies 59.9 V, 39.5% of expected (for 1mm gap). About the same for all positive biases.
      • Luke Gain even smaller for negative biases. Example: -250V data, Luke gain implies 24.5 V, 16.5% of expected. This was also seen in Run 69
      • Initial look at noise sigma versus HV
    • Still to do:
      • initial observations suggest noise sigma is lower with lower event rate. Use source to study relation of noise to event rate.
      • HV troubleshooting…
      • Try using the source mover, take position-dependence data
    • Weekend transfer planning.
  • PuBe storage shielding
  • Budget overage: we have something like $20,000 we could spend on lab stuff before April 1
    • Buy equipment/supplies:
      • New idea: get a new LHe transfer stick? Janis standard-model (one piece) = $2200, we may want a custom model instead.
      • Replacement forepump for leak detector
        • This pump is discontinued - instead we shipped ours to Pfeiffer for repair
      • Send out spare circulation pump for leakcheck/repair
      • Two lab computers replaced
      • NbTi cables for tower-free detector&cold electronics mounting
        • could get 2@25-wire for 4K-CP, 2@25-wire for CP-MC. And maybe 2@25-wire, longer, to try 4K-MC (colder SQUETs)
      • SQUIDs for new cold electronics
      • Copper-clad NbTi bell wire for a new source mover motor - quote at $930 for one motor
    • Budget spend-down Spreadsheet
  • Analysis status:
    • Run 71
    • Run 68 (n,gamma with S101)
      • Migdal analysis pending
      • New (n,γ) simulations, modified signal shape
    • NaI studies
      • tried to see Si n-capture gammas with a bag of sand - nothing seen
      • assessing the howitzer for PuBe storage - definitely doesn't shield gamma as well as paraffin drum and lead box
    • Run 70
      • analysis team includes Pramod, Matt, Zach - should coordinate, have meetings
      • Need to look at the recent PuBe data, work on a low-threshold energy quantity, see if we can see a hint of (n,γ) signal. Also develop cuts and look for low-energy junk
      • Will study the activation peak background
    • Run 67 (USD detector with novel time-dependent gain)
      • Dongming has characterized lots of microscopic processes, wants us to write a paper
      • Matt working on rough model of detector behavior
    • SiHV event reconstruction
      • Derek working on this
      • Hongguang developing connection to DMC
  • Future runs?
    • Re-run USD1?
      • use Co source
      • experiment with varying the amount of shield, distance of Ba source, see how background rate affects time variations in gain
      • maybe use source mover
    • Position reconstruction with source mover
      • improve motor heatsinking?
      • run with GeHV prototype - would probably want to rebond it for standard direct contact biasing
      • some day get a SiHV prototype again, run with that
    • Improved neutron calibration runs
      • under discussion with Anthony - working on grant proposal for new measurements with more NaI and whatever other improvements
      • more NaI coincidence detectors
      • can we improve Ge?
        • try again with standard bias, maybe no-tower setup?? Would this improve it?
        • try polishing bias side for “true” vacuum interface?
        • or - use a HVeV detector? can we get a high enough signal rate?
      • or should we re-do SiHV? with one of the new “pathfinder” detectors, whichever they give to us
    • Future 150mm runs
      • 150mm w/phonons - we considered designing new 600mK rod to accommodate 150mm cans. Could rethink this in terms of no-tower setup maybe…
      • We have 4/3-inch DIBs from TAMU - now we can house either detector for phonon readout (would need to machine faces on 4/3-inch housing for DIBs)
      • S1501 and S1502 sent back to TAMU
      • We have decided we can run 8 phonon channels
        • Preferred DIB-pad layout: two DIBs separated by 120 degrees
        • Himangshu's mask design: PDF download
        • Will use existing vacuum-interface electrode, mounted on side opposite the phonon side
        • Will connect directly to two DCRCs, with one diverter board to route one tower wire to HV connection
        • We'll want LEDs - are there some mounted on the DIBs? We can mount external LEDs too - existing electrode has mounts.
      • First 150mm phonon detector will be monolithic, but “donut+hole” arrangement (active veto) proposed as well.
      • Last discussion of this was a year ago, we were aiming for May 2019 to fab a detector
    • Future HVeV runs?
      • Berkeley can help us with a Soudan-style housing mount (3“ or 4”?)
      • then use original tower, can try different heatsinking for colder SQUID card
      • would need to install optical fiber
        • through top or through stripline tube?
  • Should we design and build new cold hardware?
  • SQUET recall
    • Martin wants 5 of our 9 SQUETs sent back to Colorado. He wants good SQUIDs.
    • A lot of issues to deal with:
      • there are bad SQUID chips
      • we need to change shunt resistances for iZIPv6 versus HV, but don't want to wirebond too many times
      • some SQUETs have problems at the pins
        • can we get spare SQUETs with the SQUID chips removed? Could theoretically glue good SQUID chips onto good SQUET.
    • Anthony says we may be able to get alternative SQUID chips
    • We have 1.5-ish months to deal with this
  • Lab and infrastructure
    • Leak detector: After pump rebuild, pump no longer turned. Jake and Derek fixed this problem. However, it still doesn't seem to be able to pull a good vacuum. Using scroll pump assist in order to use leak detector.