2019/05/01 (Wednesday)
| Status | LN2 transfer yesterday, second attempt after discovering a blockage Friday. Mixture has been cleaned ## times. |
|---|---|
| Setup | DIB1/3/4 → 3.2 MHz filters 2/3/1 → cable 3/1/2 |
| 0930 | MC(Cernox) = 120.3 K, Sorb = 133.8 K, IVC = 1.6 mbar, G1 (fridge) = 621.0 mbar, Level resistor = 1.183 kΩ. DIB4 pD SQUID = 800 MΩ when first measured with the Fluke multimeter. Then tried the Wavetek multimeter - read 1.375 kΩ. Then back the the Fluke, and it's reading 1.371 kΩ. I guess maybe it will be OK. |
| 0930 | Begin pumping out IVC with scroll pump, then switch to turbo pump |
| 0935 | Fire up leak detector, seems to be working today |
| 1010 | Quick electrical check of phonon-related channels and LEDs - looks good, no opens or leaks seen. |
| 1015 | Leak detector on IVC = 2000 pbarL/s with turbo valved out, = 370 pbarL/s with turbo pumping. Should let it pump down more. |
| 1025 | Tried stopping the leak detector, then running the calibration. But it seemed unable to pump below 10 mbar on “P1”. Then going back to leak detection mode it no longer seems to be able to get to base pressure. Tried multiple times venting and restarting, but now it seems stuck. I've been wondering if it's a sticky valve or something. Today makes it seem like the pump is not having problems, but that something is changing randomly, so maybe it's a valve. In leak detection mode it says P2 = 10 or 11 mbar when in the bad mode - normally this is around 5e-2 mbar or lower. |
| 1055 | Turbo on IVC = 1.9 nbar. With turbo valved out for a few minutes IVC = 19 nbar. |
| 1155 | Restart leak detector. During warmup, P1 falls to 2-3 mbar, so that already seems like an improvement. Start in leak detection mode right away - “P2” reads 4.9e-3 mbar, leak signal around 1 pbarL/s. We'll leave it running rather than check the calibration or do a new calibration, don't want to risk it failing again. |
| 1200 | Leak detector on IVC = 1400 pbarL/s with turbo valved out, = 250 pbarL/s with turbo pumping. |
| 1305 | Leak detector on IVC = 1300 pbarL/s with turbo valved out, = 210 pbarL/s with turbo pumping. |
| 1315 | IVC = 1500 pbarL/s. |
| 1315 | Begin blowing out LN2. Main bath (G3) = 423 mbar above 1atm. |
| 1325 | Main bath (G3) = 417 mbar +1atm, IVC = 1470 pbarL/s. |
| 1328 | Main bath (G3) = 250 mbar +1atm and falling, IVC = 1460 pbarL/s. |
| 1335 | Main bath (G3) = 137 mbar +1atm and flat, IVC = 1430 pbarL/s. I think we're done. Stop pressurizing main bath. |
| 1340 | Start pumping out main bath with scroll pump. IVC = 1380 pbarL/s. Takes 10 minutes to fall to 1 mbar. |
| 1350 | IVC = 1330 pbarL/s. |
| 1355 | Pressurize MB with helium to 324 mbar above 1 atm. Open 1K Pot speedivalve and needle valve (2 full turns) to repressurize pot as well. No noticeable drop in pressure when I do this. Close 1K Pot valves again. IVC = 1300 pbarL/s. |
| 1400 | Fill LN2 cold trap bath. |
| 1410 | Mini-throughput check: close off Trap 2 and V3. Only V1, condenser speedivalve, still gate valve, and V9 open. 3He pump is on. Open V6 to 12.8%. This pumps mix out of the still side and we can see if the pressure goes down on the condenser side. P1 (still) falls to 1 mbar after a few minutes. G1 (condenser) is not falling. After 5 minutes, P1 (still) is down to 0.040 mbar but G1 (condenser) is hanging near 611 mbar, falling by 0.2 mbar at most. Looks like a blockage, again. |
| Throughput test procedure, Cold Trap 2: |
- All mixture in dump, LN2 trap 2 cold, condenser & still valves open (3He pump on - optional)
- Open V9, V13b, V12b+speedivalve, V3. Wait for G1 to be close to G2.
- Close V12b+speedivalve and V3, open V1
- monitor G1
| 1420 | Perform mixture throughput test at MC = 77 K using above procedure with 3He pump on. Let G1 rise to 525 mbar before Step 3, then it falls to 32 mbar, rises very slowly. Throughput ~ 0.11 mbar/min. Compare Run 68 where we got 35.7 mbar/min. |
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| 1425 | Another blockage. Gotta warm up again. |
| 1425 | Turbo on IVC: 1.9 nbar. Stop pumping out IVC. IVC → 25 nbar after a few minutes. |
| 1435 | Pump mixture from fridge to dump. |
| 1445 | Let about 0.17 bar nitrogen into IVC. MC temperature rises, 77.7→78.0 K. Close off IVC. |
| 1445 | Isolate fridge and 4He trap. Pump mixture from LN2 Cold Trap 2 to dump. |
| 1500 | Investigate leak detector. P1 is the forepressure, P2 is the test port pressure. During the test, V4 (port to turbo) and V1 (turbo to forepump) open, P1/P2 = 13/2.9e-3 mbar. These are both pretty high. Looks like a too-high forepressure, which is compromising the turbo. I had noticed that the IVC pressure went up a little when I pumped on it with the LD, even when the turbo pump was still pumping on the IVC. That's not normal. Stopping the test, I saw V4 close. So it stops pumping on the port. Try a calibration. P2 fails to fall below 10 mbar so it doesn't start. Try another leak test. V2 (port to rough pump) opens, to rough pump the test port. Presumably this should eventually switch over, closing V2 and opening V4 to pump with turbo. But it doesn't happen, I guess because it's waiting to fall below 10 mbar. Conclusion: forepump is not working well for some reason. Can't seem to pump much below 10 mbar. It's probably not the gauges misreading, because P1 and P2 agree when they are connected. |
| 1510 | Connect vacuum hoses to cryostat vacuum jacket and pump them out. |
| 1510 | MC(Cernox)/Sorb = 79.0/151.7 K |
| 1515 | Let 200 mbar (on digital gauge) N2 gas into vacuum manifold. Then open cryostat vacuum jacket valve to let this into the vacuum jacket. Vacuum jacket → 8.6 mbar |
| 1515 | LN2 Trap 1 is warm. Check contents: 10.1-0.8 = 9.3 mbar on G1. Pump out with 4He pump. |
| 1545 | More investigation of the leak detector. There is a clear plastic hose with metal reinforcement from the rough pump inlet to the manifold unit. The inlet is a KF port, with a KF-to-hose barb adapter, then the hose, then a hose barb on the other end. We removed the KF connection and the hose clamp on the other end and inspected the hose. Looks OK. Clamped it to our turbo pump manifold, at the adapter where we let in exchange gas, blanked the KF end, and pumped it out with the scroll pump. Pumps down to 1.9e-2 mbar with no problem. Valve out the pump, after several minutes pressure rises only to 5.4e-1 mbar. A lot better than 10 mbar. So probably this hose is not the problem. |
| 1600 | Try connecting LD rough pump to our vacuum manifold. Pumps down to 2.5 mbar, which is better than 10 mbar, but it's not very low. Starting to think the pump needs servicing. |
| 1600 | MC(Cernox)/Sorb = 84.3/184.2 K |
| Last time we kept the fridge isolated during the warmup and checked the fridge pressures afterward. They weren't very high, and we probably won't learn much doing this again. So instead maybe we can try throughput tests at various temperatures. | |
| 1625 | Perform mixture throughput test at MC = 89 K using previous procedure except through Trap 1 with 3He pump on. Let G1 rise to 575 mbar before Step 3, then it falls to 33 mbar, rises very slowly. Throughput ~ 0.05 mbar/min. Even worse than before. |
| 1735 | Main bath pressure had risen above 1000 mbar +1atm on G3 an hour ago. Let the pressure out now. Cover port with plastic cap weighted with KF o-ring. |
| 1740 | MC(Cernox)/Sorb = 103.6/241.2 K warming time constant around 17 hours, should hit 10 celsius 4pm Friday. |