2019/04/26 (Friday)
| Status | LN2 transfer yesterday. LN2 Cold Trap 2 is warm and still has contaminants from last cleaning. |
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| Setup | DIB1/3/4 → 3.2 MHz filters 2/3/1 → cable 3/1/2 |
| 0850 | MC(Cernox) = 79.7 K, Sorb = 143.4 K, IVC = 1.6 mbar, G1 (fridge) = 622.6 mbar, Level resistor = 1.184 kΩ |
| 0850 | Start pumping out IVC with scroll pump. After a couple of minutes switch to turbo pump. |
| 0920 | Perform electrical check on DIBs 1,3,4: |
PROBLEM: DIB4 pD SQUID = 800 kΩ and fluctuates. Should be 1-2 kΩ- Initially DIB4pD SQUID read too high. But switching the leads, it showed a normal resistance - and switching them back, it was OK too.
- Every time we plug it in it's slightly different, 1.9-2.1 kΩ - others are more stable. But it seems good enough. We'll try. (Note this is Side1pF.)
- The HV wires on DIB4 QET A read 102 Ω. Other QET-QETbias lines on this stripline read around 45 Ω, so looks like the tower wiring is around 57 Ω.
| 0940 | Turbo on IVC: 5.4 nbar. |
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| 0940 | Leak detector seems to be having trouble again. When I try to run Calibration, the pumpout seems to hang up at around 11 mbar. When I run a test with the port blanked, signal is in the 1e-4 mbarL/s range (100,000 pbarL/s). We'll try power cycling. |
| 0950 | ERROR (56) p1 > 10 mbar after runup Possible causes: > Forepump is faulty > Valve V1 did not open |
| 1040 | Try leak detector again, same error |
| 1040 | The Alcatel leak detector is not available for another hour. Trying to decide whether to skip the leak check and just blow out the LN2. |
| 1050 | Begin blowing out LN2. Main bath (G3) = 455 mbar above 1atm. (Helium cylinder is low, we'll probably run it out and need to switch over). |
| 1055 | Main bath (G3) = 431 mbar above 1atm. |
| 1100 | Main bath (G3) = 130 mbar and falling quickly. Close V1a to the main bath - G3 pressure does not increase. So I guess the cylinder is empty. |
| 1105 | Switch helium cylinders and pressurize bath again. Main bath (G3) → 230 mbar +1atm. |
| 1110 | Main bath (G3) = 137 mbar +1atm and flat. I think we're done. Stop pressurizing main bath. |
| 1115 | Start pumping out main bath with scroll pump. Takes 12 minutes to fall to 1 mbar. |
| 1135 | Pressurize MB with helium to 365 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. |
| 1140 | Mini-throughput check: close off Trap 1 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 0.036 mbar but G1 (condenser) is hanging near 614 mbar, falling by 0.5 mbar at most. Looks like a blockage. |
| 1145 | Pump mixture from fridge to dump. |
| Throughput test procedure, Cold Trap 1: |
- All mixture in dump, LN2 trap 1 cold, condenser & still valves open (3He pump on - optional)
- Open V9, V13a, V12a+speedivalve, V3. Wait for G1 to be close to G2.
- Close V12a+speedivalve and V3, open V1
- monitor G1
| 1155 | Perform mixture throughput test at MC = 77 K using above procedure with 3He pump on. Let G1 rise to 550 mbar before Step 3, then it falls to 32 mbar, doesn't rise. Throughput < 0.1 mbar/min. |
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| 1200 | We have a blockage. Guess I didn't clean the mixture thoroughly enough. Need to warm up. |
| 1200 | Pump mixture out of fridge to dump. |
| 1210 | Isolate fridge and LHe trap (by closing Still gate valve, Condenser speedivalve, and V1). |
| 1215 | Pump mixture from LN2 Trap 1 to dump. |
| 1215 | Turbo on IVC: 4.6 nbar. Stop pumping out IVC. IVC → 86 nbar after a few minutes. |
| 1220 | Let helium into IVC. Around 10 mbar I think - then the Pfeiffer gauge ran off scale for some reason. Mechanical gauge on turbo pump manifold is pegged low so it's probably less than 30 mbar. MC(Cernox) temperature starts to rise, 79.4→80.3 K and rising. |
| 1230 | LN2 Trap 2 is warm. Check contents: 6.0-0.8 = 5.2 mbar on G1. Pump out with scroll pump. |
| 1250 | MC(Cernox)/Sorb = 85.2/161 K and rising |
| 1250 | Start cryocleaning mixture through LN2 Cold Trap 2, V6 = 12.7% |
| 1255 | Increase V6 → 12.9% to restart flow |
| 1320 | Increase V6 → 13.0% to speed up flow |
| 1355 | Stop cleaning through Trap 2 after 65 min. G2 flow pressure was 585-645 mbar. Pump mixture to dump. Removed 4.1 mbar |
| 1310 | Isolate IVC then connect vacuum hoses to cryostat vacuum jacket and pump them out. |
| 1315 | MC(Cernox)/Sorb = 87.4/164.3 K |
| 1315 | Let 200 mbar N2 gas into vacuum manifold. Then open cryostat vacuum jacket valve to let this into the vacuum jacket. Vacuum jacket → 5.4 mbar |
| 1325 | MC(Cernox)/Sorb = 88.4/168.1 K. Warming rate has clearly risen especially at sorb. Also see main bath pressure rising, MB = 581 mbar +1atm |
| 1355 | MC(Cernox)/Sorb = 93.7/188.6 K. MB = 784 mbar +1atm |
| 1410 | MC(Cernox)/Sorb = 96.4/196.9 K. MB = 841 mbar +1atm this is the highest I've ever seen G3. Have been watching the mechanical gauge above the fridge too - it looks like G3 reads about 2.2 times as high as the mechanical gauge, assuming standard PSI-to-mbar conversion. |
| 1230 | LN2 Trap 1 is warm. Check contents: 7.7-0.2 = 7.5 mbar on G1. Surprisingly high since this is not after a cleaning, it's just from the mixture sitting there overnight. Pump out with 4He pump. |
| 1435 | MC(Cernox)/Sorb = 102.8/213.6 K. MB = 950 mbar +1atm |
| 1435 | Start cryocleaning mixture through LN2 Cold Trap 1, V6 = 13.0% |
| 1450 | Increase V6 → 13.2% to restart flow |
| 1505 | Increase V6 → 13.3% to speed up flow |
| 1540 | Stop cleaning through Trap 1 after 65 min. G2 flow pressure was 580-820 mbar. Pump mixture to dump. Removed 6.0 mbar |
| 1455 | MC(Cernox)/Sorb = 106.6/222.4 K. MB = >999 mbar +1atm, apparently that's the max. MB = 6.9 PSI on mechanical gauge. Let the pressure out of the MB by taking one of the stoppers out for a couple seconds, then replace it. |
| 1500 | MC(Cernox)/Sorb = 108.7/226.5 K. MB = 278 mbar +1atm, rising again. |
| 1500 | MC warming time constant is around 13.9 hours, should be around 10 °C by 5 am Sunday the 28th. |
| 1530 | Have been looking at DIB4 pD SQUID occasionally, was fine till now - now it's reading high again. Looks worrisome. Note that this is the SQUET with the HV lines, so it's the one that I pulled the SQUID card over to the next position on the 600mK stage. So the flyover cable is a little stressed. |
| 1600 | LN2 Trap 2 is warm. Check contents: 4.4-0.3 = 4.1 mbar on G1. Pump out with 4He pump. |
| 1610 | MC(Cernox)/Sorb = 123.4/>249 K. MB = 437 mbar +1atm. Remove stopper from MB port, don't want the pressure to rise too much. Replace with a plastic KF cover weighted down by a KF o-ring. MB → 96 mbar +1atm. |
| 1620 | Close V9, then turn off 3He pump. So almost all mix is in the dump. |
| 1700 | LN2 Trap 1 is mostly warm. Check contents: 6.5-0.5 = 6.0 mbar on G1. Pump out with 4He pump. |
| 1710 | Check DIB4 pD SQUID again. It looks good now. Comes and goes… |
| 1720 | Open V4 and V12B + speedivalve, to let mixture from dump to cold LN2 Trap 2. This is to “passively” clean the mix over the weekend. (will need to top off the LN2.) |