2021/02/17 (Wednesday)

Previous Day

• Lab in-person: Matt
• Virtual partner: Ruiren

1. All mixture in dump, LN2 trap 2 cold, condenser & still valves open (3He pump on - optional)
2. Open V9, V13b, V12b+speedivalve, V3. Wait for G1 to be close to G2.
3. Close V12b+speedivalve and V3, open V1
4. monitor G1

1235	Perform mixture throughput test at MC = 77 K using above procedure with 3He pump on. Let G1 rise to 560 mbar before Step 3, then it falls to 61 mbar, then rises. Throughput = 43.2 mbar/min. A little higher than last time, 2020 Oct 7
1240	Open mixture to both sides of the fridge and cold LN2 Trap 2.
1240	Try Leak Detector on IVC, with Turbo still pumping in parallel. (We've only been pumping out the helium for 35 minutes.) LD = 137 pbarL/s. With Turbo valved out, LD → 1100 pbarL/s. Open Turbo valve to continue pumping IVC.
1255	Perform electrical checkout at breakout box on DIBs 1/2 (Cables 2/3). Everything looks good EXCEPT: 12 nS short from qI Feedback to Chassis
1300	Leak on IVC with Turbo pumping: 119 pbarL/s. With Turbo valved out → 1050 pbarL/s.
1315	Leak on IVC with Turbo pumping: 110 pbarL/s. With Turbo valved out → 1070 pbarL/s.
1325	Begin blowing out LN2. Main bath (G3) → 760 mbar+1atm. (Helium cylinder is low, we'll probably have to swap to a fresh one.)
	Setup during LN2 blowout. Recovery hose is attached to bath outlet to pressurize it. LN2 is collected in 25L storage Dewar, with hose not too deep in the Dewar so that the Dewar can be moved aside if it starts to overflow and the other one can be moved in.
1330	IVC = 954 pbarL/s, MB = 708 mbar+1atm
1335	IVC = 899 pbarL/s, MB = 360 mbar+1atm and falling. Falls to 100 mbar. Close V1a: G3 doesn't rise. So cylinder must be empty.
1340	Swap to fresh He cylinder and continue LN2 blowout
1345	IVC = 881 pbarL/s, MB = 236 mbar+1atm. Pretty low - probably the blowout is about finished.
1345	Stop LN2 blowout
1350	Fill LN2 cold trap bath
	remove hose from MB LN2 fill pipe and put stopper in pipe, for MB pumpout
1350	Start pumping out main bath with scroll pump. Takes 9 minutes to fall to 1 mbar.
1405	Pressurize MB with helium to 220 mbar above 1 atm.
1405	Isolate MB by closing V1a. Pump out line to the G3 volume with Scroll Pump. Isolate pump, then open 1K Pot speedivalve to check pressure: about 0.04 bar. Then pump out 1K Pot (needle valve closed) with Scroll Pump to 0.024 mbar on P2. Then close 1K Pot speedivalve and V4a. Open V1a again to monitor bath pressure.
1415	Running into a problem with the webcam: the computer jiajin was replaced, and the webcamautomater won't work on the new machine, says it can't find “ffmpeg”. Plugged the camera into the fridge windows computer. Now I can use the native Camera app. This can be set to take pictures every 2, 5, or 10 seconds repeatedly.
1420	Turbo on IVC = 3.4 nbar. With Turbo valve out for a minute, IVC = 46 nbar
1425	Let 63 μbar He exchange gas into IVC.
1425	MC(Cernox) = 77.8 K, Sorb = 142.4 K, IVC = 63 μbar, G1(fridge) = 624.5 mbar. G3(MB) = 192 mbar+1atm.
1453	Begin initial LHe transfer
1500	Turn on heater on 250L LHe Dewar
1500	MC(Cernox) = 79.9 K, Sorb = 153.8 K, IVC = 63 μbar, G1(fridge) = 624.4 mbar. G3(MB) = 534 mbar+1atm.
1510	MC(Cernox)/Sorb/1K Pot = 77.5/139/>7 K, IVC = 19 μbar, G1(fridge) = 617.5 mbar. G3(MB) = 408 mbar+1atm.
1525	MC(Cernox)/Sorb/1K Pot = 67.1/100/>7 K, IVC = 12 μbar, G1(fridge) = 583.4 mbar, MB = 3.9% / 492 mbar+1atm.
1530	Monitoring the recovery system bag online (first time I ever did this), I noticed it hit 99%. Instructions from P Crowell are that if it creeps above 95%, you should slow down your transfer. Oops. Turn off LHe Dewar heater, we'll let the MB pressure settle a bit.
1540	MC(Cernox)/Sorb/1K Pot = 58.0/50/>7 K, IVC = 8.6 μbar, G1(fridge) = 493.7 mbar, MB = 7.2% / 456 mbar+1atm.
1545	Noticed that the extender for the transfer line had slid all the way down into the Dewar top port, and it was touching the bottom. It stayed up with the old transfer line I think because there was some tension and the torque held it up - this one is more flexible, so less tension. I stuck a piece of poly between the extender oring bracket and the top port to hold it up a few inches.
1550	MC(Cernox)/Sorb/1K Pot = 51.1/8.1/6.4 K, IVC = 7.4 μbar, G1(fridge) = 485.1 mbar, MB = 6.9% / 380 mbar+1atm.
	MB pressure has dropped to its lowest point now with the Dewar heater off. Dewar pressure gauge is down to 3 PSIG. The bag level is still around 99%. Notice that the MB level has gone down a little - that sucks. Maybe that's just from the transfer line having dropped to the bottom, and now it will start to go up again. Hopefully the line isn't plugged.
1600	MC(Cernox)/Sorb/1K Pot = 46.1/7.3/5.9 K, IVC = 6.3 μbar, G1(fridge) = 482.7 mbar, MB = 5.2% / 357 mbar+1atm.
	Not sure what to do - transfer is now slow, but bag level is still high. I went to the recovery room to look at the bag, and it certainly looks full - and only one compressor is on, the second one is supposed to automatically switch on when the height gets high. Emailed Mike Rother but haven't heard back.
1605	Recovery meter rate: 1 cuft / 7.52 seconds. MB = 344 mbar+1atm
1605	Turn Dewar heater back on, we'll see what happens.
1610	Recovery meter rate: 1 cuft / 5.62 seconds. MB = 431 mbar+1atm
1615	MC(Cernox)/Sorb/1K Pot = 37.7/7.0/5.6 K, IVC = 6.3 μbar, G1(fridge) = 471.7 mbar, MB = 23.2% / 442 mbar+1atm.
1620	Recovery meter rate: 1 cuft / 4.82 seconds. MB = 440 mbar+1atm
1625	MC(Cernox)/Sorb/1K Pot = 30.7/6.6/5.4 K, IVC = 6.3 μbar, G1(fridge) = 467.2 mbar, MB = 52.2% / 434 mbar+1atm.
1635	MC(Cernox)/Sorb/1K Pot = 24.0/6.3/5.1 K, IVC = 8.6 μbar, G1(fridge) = 464.2 mbar, MB = 78.3% / 428 mbar+1atm.
	IVC pressure seems to have increased, odd
1640	MC(Cernox)/Sorb/1K Pot = 20.6/6.2/5.0 K, IVC = 8.6 μbar, G1(fridge) = 462.9 mbar, MB = 90.7% / 418 mbar+1atm.
1647	End LHe transfer @ MB = 85.2%
	note: the level read 100% before ending the transfer, so this is a big drop. Possibly we lost significant LHe while trying to deal with the new transfer line (see below)

Notes on the new transfer line:

• The flexible part is more flexible, so that there is less tension in the transfer Dewar port, using the 250L Dewar. So the extender tends to slide all the way down. I propped it up with a small piece of poly.
• The cap to close off the cryostat piece after disconnecting the Dewar piece gets way too cold, and has a hole in it that squirts out cold He gas radially out as you are trying to turn it. So I didn't bother trying to cap it - so LHe just sorta poured out until I could get the other end taken care of, then I just pulled out the cryostat piece without capping it.
  • If we can't figure out a way to cap it, then we should change procedure: after disconnecting, immediately remove the cryostat piece and stopper the port. Then deal with the Dewar piece.
• The flexibility also makes the hooks a little wonky compared to before. When I hooked the side near the Dewar, the hose slid down kinda far on the other hook. I'll need to figure out how to make this work a little better.

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