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2021/12/01 (Wednesday)

Previous Day

  • Lab in-personnel: Giulia, Matt, Himangshu
Status Beginning Run 75. LN2 transfer yesterday. Cryostat vacuum jacket (CVJ) pumped out.
0845 IVC = 1.6 mbar. Start pumping IVC with Scroll pump, @ 0.1 mbar switch to Turbo.
1055 MC(Cernox) = 77.1 K, Sorb = 130.1 K, G2/G1 (fridge+trap1+dump) = 560/602 mbar, 3He pump off.
Tower/Goldman thermometers = 1.0369/2.1888 kΩ.
1100 Turn on 3He pump and open V6 to 12.6%, reestablishing circulation like yesterday. G2/G1/P1 → 682/735/1.7 mbar and settle
1105 Close V12a speedivalve for 2 minutes to assess throughput. G1 falls at 63.6 mbar/min, good. Reopen V12a speedivalve.
1110 Pump mixture from fridge and Trap 1 to Dump
Throughput test procedure, Cold Trap 1:
  1. All mixture in dump, LN2 trap 1 cold, condenser & still valves open (3He pump on - optional)
  2. Open V9, V13a, V12a+speedivalve, V3. Wait for G1 to be close to G2 (within 100 mbar).
  3. Close V12a+speedivalve and V3, open V1
  4. monitor G1
1115 Perform mixture throughput test at MC = 77 K using above procedure with 3He pump on. Let G1 rise to 543 mbar before Step 3, then it falls to 69 mbar, then rises. Throughput = 42.4 mbar/min. Nearly the same as last time, 2021 June 10
1120 Open mixture to both sides of the fridge and cold LN2 Trap 1.
1120 Turbo on IVC = 6.3 nbar. With Turbo valved out for 1 minute, IVC = 100 nbar.
1125 Try Leak Detector on IVC, with Turbo still pumping in parallel. (We've been pumping out the helium for 2 hr 40 minutes.) LD = 510 pbarL/s. With Turbo valved out for a minute, LD → 2200 pbarL/s. Not as good as last time. Open Turbo valve to continue pumping IVC.
1150 IVC = 470 pbarL/s with turbo, 2000 pbarL/s without turbo
1155 Perform electrical checks on all 3 cables. All looks good except: Cable 3 Feedback A too high, 0.8 MOhm, should be around 10 kOhm.
This same feedback resistor read high at 77K the last time this SQUET, ZC-70, was used, in Run 71 - with iZIP G106a. Side1 pB in that run - it seems to have worked fine.
1245 IVC = 411 pbarL/s with turbo, 2000 pbarL/s without turbo
The LHe liquefier was down the last couple weeks, but is now running again. We thought there'd be LHe today but we won't have any till tomorrow, so we have to delay one day. To keep the fridge at 77K we probably want to add more LN2 - not sure how long till it boils off.
1510 Tower/Sorb = 77.2/130.9 K
1510 Set up for another LN2 transfer. Insert level resistor and let the value stabilize.
1510 Level resistor = 1.235 kOhm.
1515 Start LN2 transfer. Level resistor immediately rises, → 1.305 kOhm.
1520 Level resistor = 1.335 kOhm.
1525 Fill LN2 cold trap bath. (Used the 5L Dewar, filled it in the fill room.)
1535 Sorb = 130.3 K (down a little), Level resistor = 1.332 kOhm.
1550 Looks like we ran out of LN2 in the Dewar.
1550 Sorb = 130.0 K, Level resistor = 1.286 kOhm.
1600 Close LN2 Dewar valve. Pull out Level Resistor and put stopper in port. Put ping-pong ball on MB exhaust port.

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