2015/03/24
| 0926 | Dump at 700 mbar. C/w yesterday, 653 mbar: apparently 47 mbar added. (Yesterday it appeared to be 42 mbar but maybe it was still below room temperature). Mixture before/after = 653 mbar (25% 3He) / 700 mbar (23% 3He) |
|---|---|
| 0950 | Fill LN2 cold trap full. |
| 1000 | With P2=80 ubar, pull He cold trap from bath and open to P2 (scroll pump speedivalve closed). |
| 1015 | 4.5 mbar worth of contaminate collected in P2 from He cold trap. Open scroll pump speedivalve to begin pumping on He cold trap. |
| 1030 | Isolate He cold trap, close scroll pump speedivalve, pull LN2 codl traps from bath and open to P2. |
| 1100 | 90 mbar worth of contaminate collected in P2 from He cold trap. Open scroll pump speedivalve to begin pumping on N2 cold traps. |
| 1115 | Finish round of cold trap cleaning. Open He cold trap to scroll pump. |
| 1147 | With a background leak rate of 4.5E-9 mbarL/s, conduct a leak check on IVC. When opening IVC to leak checker, leak rate dropped to 3E-9 mbarL/s. System was obviously cryopumping, so pump on IVC with turbo pump for a moment and then isolate IVC to reduce further gas entering the IVC. |
| Start 1K Pot. | |
| 1200 | G1=1.5 mbar, P1=2 mbar, G2=703 mbar, Mixing chamber at 15.3 K, and 1K Pot is at 1.74 K, Sorb is at 4.0 K. Commence condensation procedure through cold trap 1. |
| 1440 | G1=144 mbar, P1=45 ubar, G2=143 mbar, Mixing chamber at 382 mK and slowly rising, Still is at 1.05 K, and 1K Pot is at 1.80 K. Close V14 since all mixture has been taken from dump. |
| 1444 | Adjust 1K Pot down to 1.53 K. Still temperature at 881 mK, G1=81.6 mbar, G2=85 mbar, P1=150 ubar, P2=4.5 mbar. |
| 1510 | Still heat set to 6 mW, Still temperature at 980 mK, mixing chamber temperature 384 mK, 1K Pot is at 1.58 K, G1=114 mbar, G2=122 mbar, P1=280 ubar, P2=6 mbar. |
| 1530 | Still heat set to 10 mW, Still temperature at 1.06 mK, mixing chamber temperature 338 mK, 1K Pot is at 1.58 K, G1=121 mbar, G2=132 mbar, P1=320 ubar, P2=6 mbar. |
| 1550 | Still heat set to 14 mW, Still temperature at 1.11 mK, mixing chamber temperature 322 mK, 1K Pot is at 1.59 K, G1=131 mbar, G2=143 mbar, P1=360 ubar, P2=7 mbar. |
| 1620 | Still heat set to 20 mW, Still temperature at 1.18 mK, mixing chamber temperature 311 mK, 1K Pot is at 1.62 K, G1=136 mbar, G2=155 mbar, P1=400 ubar, P2=9 mbar. |
| 1640 | Still heat set to 27.5 mW, Still temperature at 1.25 mK, mixing chamber temperature 306 mK, 1K Pot is at 1.63 K, G1=168 mbar, G2=185 mbar, P1=500 ubar, P2=10 mbar. |
| 1650 | Adjust 1K Pot. G1 and G2 climbing above 200 mbar quickly, reducing still heater back down to 22 mW. Around this time (but possibly before), mixing chamber temperature dropped to 296 mK. After several minutes 1K Pot begins to increase rapidly and P2 pressure dropped, suggesting it is running dry. Open 1K Pot needle valve further. |
| 1705 | Still heat set to 25 mW, Still temperature at 1.24 mK, mixing chamber temperature 296 mK, 1K Pot is at 1.69 K, G1=198 mbar, G2=211 mbar, P1=500 ubar, P2=20 mbar. |
| 1715 | Still heat set to 26 mW, Still temperature at 1.23 mK, mixing chamber temperature 296 mK, 1K Pot is at 1.68 K, G1=172 mbar, G2=189 mbar, P1=500 ubar, P2=19 mbar. |
| 1720 | Close V13, open V9 to attempt single shot test with still heater left on at 26mW. Mixing chamber temperature did not decrease, but simply increased during this test. |
| 1726 | Mixing chamber peaked at 450 mK during single shot test and then started to drop. It dropped to roughly 380 mK before rising again. |
| 1731 | P1 plummets indicating still is empty. G2 = 170 mbar. MC rising steadily, at 1.1 K. Turned off still heater; P1 continues to drop and MC continues to rise. |
| 1739 | Turned off 1KPot, turned on the MC heater to 20 mW. Recovering mixture. |
| 1850 | With G1= 2.7 mbar, G2= 657 mbar, P1= 30 ubar, close gate valve and condenser line speedivalve. Turn of MC heater and close all valves on IGH. |
It's interesting that during recovery P1 dropped when G2 was at 170 mbar - this is close to the total amount of 3He (25% of 650 mbar). So it could be that the drop was not due to the still emptying but rather caused by the exhaustion of 3He, so that 3He-cooling stopped (MC had risen to low 1KPot temperature, so 4He vapor pressure would be very low). It could be that the still emptied sooner than this and that the total amount of mixture is still too low.
Today's test indicates that adding more 4He improved performance: the fridge reached the lowest base so far this year (296 mK) and ran stably, without oscillation. Still heating tests proved more successful than previous attempt, performed on 2015/03/05. Still far from target. We'll try adding still more 4He.