2020/08/18 (Tuesday)
- Lab in-person:
- Virtual partner:
| Setup | Run 73. DIB 1/3/4 → Stripline 43/48/41 → pi-filters 1/2/3 → Cable 3/1/2 → nothing/nothing/accessory_interposer → HV_Conn 1/3/2 → HV 1/2 → DCRCX(4)/DCRC55(1)-master; DCRC33(2) → HV control. DCRCs on overnight. Lead/poly shield erected (4 lead walls, 2 poly walls). |
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| Status: Added more 4He to the mixture yesterday, then cooled down again. | |
| 0720 | Tower = 0.46 K and cooling very slowly. That's not good. |
| 0720 | Tower = 0.46 K. G1/G2 = 679/619 mbar, flat. Still = 0.22 mbar / 5 mW, flat. |
| 0725 | Increase Still Heater to 10 mW. This gives a little more cooling, at least at first. |
| 0750 | Tower → 0.44 K and flattens out. G1/G2 → 717/654 mbar. Still → 0.26 mbar. |
| 0805 | Turn DCRC1 LED1 on for a couple seconds |
| 0815 | Turn off Still Heater. Tower → 0.48 K, then starts to cool a bit. Then starts rising… |
| 0850 | Tower = 0.50 K and rising |
| 0850 | Turn on Still Heater to 12 mW |
So what is wrong - why is the fridge so hot? Ideas:
- DCRC problem. We can try disconnecting them
- Helium in the IVC. Maybe some was “shaken loose” during the warming yesterday. We'd need to warm above 4 K and pump out the IVC, then try cooling again
- Mixture is now messed up. Can we reverse what we did, remove some 4He? Yes - with the fridge cool (below 1K) you can pump to dump, you'll get all the 3He first, then stop pumping when you have the desired amount in the dump. What's left in the fridge should be almost entirely 4He. You could then pump that out to recovery or something. (Should do some calculations to convince ourselves that there'd be no significant loss of 3He.)
- Could also be that dirty mixture / dirty trap is somehow messing up cooling, but seems unlikely
| 1115 | Matt Fritts body temperature 98.0 °F |
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| 1145 | Matt enters lab |
| 1150 | Tower/MC/Coldplate = 479/487/661 mK, Still = 1.49 K / 0.26 mbar / 12 mW, G1/G2= 739/675 mbar, 1K Pot = 1.64 K / 26±2 mbar. |
| 1155 | Unplug HV from HV box. Turn off DAQ programs, then power down DCRC1&4. No effect on MC temperature. MC = 0.49 K. |
| 1157 | Turbo on IVC = 2.2 ubar. Close valve to isolate IVC from Turbo. IVC = 30 nbar with Turbo valved out for 5 minutes. |
| 1200 | MB = 27.0% |
| 1200 | Turn off Still Heater. MC → 0.51 K and rising. Still → 1.32 K / 0.14 mbar. |
| Let's stop circulation and 1K Pot, warm things up, watch the IVC pressure for changes. | |
| 1205 | Close V6 to stop circulation |
| 1210 | Valve seems to be closed all the way. P1(Still) rising, G1/G2 (condenser) falling, MC temperature rising. |
| 1215 | MC = 1.0 K and rising. That definitely seems like a heat leak, not something wrong with the dilution unit. Still = 2.0 K. Warmer than 1K Pot even (1K Pot remains at 1.65 K). |
| 1215 | IVC = 25 nbar. It hasn't risen yet. |
| 1225 | MC = 1.5 K, rising less quickly now. Still = 2.15 K. Coldplate = 2.73 K. |
| 1230 | MC = 1.56 K, leveling off. |
| 1230 | Close 1K Pot needle valve. 1K Pot → 1.40 K / 2.4 mbar |
| 1235 | Close V4a to stop pumping on 1K Pot. Leave 1K Pot Speedivalve open; if it goes over 1atm we can see it on G3. |
| 1240 | MC/1K Pot = 1.70/2.03 K |
| 1240 | Open 1K Pot Needle Valve → 20°. |
| 1245 | MC/1K Pot = 1.74/2.62 K. MC looks pretty flat. No change in IVC. |
| 1245 | Turn on MC heater → 20 mW. Tower → 1.95 K |
| 1245 | G3(1K Pot) → 160 mbar+1atm. I guess the pressure is equalizing with the MB. |
| 1250 | MC/1K Pot = 2.15/2.88 K. |
| 1250 | Open 1K Pot Needle Valve → 40°. |
| 1255 | MC suddenly starts warming more quickly, 2.3→3.4 K. (Just past the lambda point?) |
| 1300 | MC/1K Pot peak at 4.0/3.1 K but then start cooling, interesting. IVC = 30 nbar, still basically unchanged. MC → 2.6 K quickly. What is cooling it? It must now be in thermal contact with something it wasn't in contact with before. The Still or the Tower. (of course MC should always be in good contact with the Tower). Tower/Coldplate/Still = 2.62/5.22/3.61 K (Coldplate & Still probably not reliable) |
| 1320 | Set up camera to take pix of IVC pressure every 10 minutes. |
| 1320 | MC/1K Pot = 3.26/3.11 K. MC is rising steadily, 1K Pot is flat. |
| 1320 | G1/G2 pressures are rising now, minimum was 130 mbar, now 260/230 mbar. May need to release pressure into dump soon. |
| 1325 | Turn off MC Heater. |
| 1330 | Open V3 to equalize mixture pressure on both sides of fridge |
| 1330 | MC/1K Pot = 3.28/3.48 K. MC is pretty flat now, 1K Pot slowly rising. |
| 1340 | Fill LN2 cold trap bath |
| 1345 | Matt leaves lab |
| 1415 | MC/1K Pot = 3.32/4.29 K. Both are pretty flat. G1/G2 = 389/352 mbar, flat. IVC = 25 nbar, still unchanged. |
| 1415 | Turn on MC Heater to 20 mW |
| 1425 | Matt Fritts body temperature 98.2 °F |
| 1500 | MC/1K Pot = 3.99/4.26 K, MC rising. G1/G2 = 786/715, rising. We'll have to release pressure to dump soon. |
| 1530 | MC/1K Pot = 4.13/4.29 K, MC rising. G1/G2 = 889/809, rising. IVC = 30 nbar, still unchanged. |
| 1535 | Turn on Still Heater to 30 mW. G1/G2 rising faster, MC rising slightly faster. 1K Pot temperature and pressure rise too. |
| 1540 | G1 = 950 mbar. Open V9 for a few seconds to release some mixture to the dump. Causes a cooling effect on MC. |
| 1550 | MC suddenly starts warming quickly, → 5.1 K and rising |
| IVC pressure finally increases: |
| 1600 | MC = 7.1 K, IVC = 46 nbar. MC temperature is now flattening out. |
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| 1605 | G1 rises above 950 mbar again, let some into dump to get G1 down to 800 mbar. |
| 1610 | MC = 7.3 K, IVC = 63 nbar. |
| 1700 | MC/1K Pot = 7.3/>7 K. MC flat. G1/G2 = 850/776 mbar, flat. IVC = 63 nbar. |
| 2010 | MC = 7.37 K. G1/G2 = 856/782 mbar. IVC = 63 nbar. |
| looks like we are in a state of equilibrium between the cooling from the bath and the warming from the heaters probably don't want to leave it this way overnight, the pressures could run away at some point |
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| 2015 | Let a little more mixture into the dump. G1/G2 → 767/651 mbar. No cooling effect seen. |
| 2150 | MC = 7.48 K. IVC = 74 nbar. Open V9 and leave it open. G1/G2 → 589/536 mbar. |