2018/06/22 (Friday)
| overnight: Tower temp unstable. Tower fluctuated between 38 mK and 58 mK, G1 is following a repeating sharkfin pattern with amplitude between 176 mbar and 127 mbar |
| 0936 | Tower/MC/Coldplate = 52.5/50.2/213 mK, Still = 1.0 K / 0.036 mbar / 0 mW, G1/G2 = 193/180 mbar, 1K Pot = 1.49 K / 5.5 mbar. MB = 70.3% |
|---|---|
| 0948 | Fill LN2 cold trap full. |
| 1017 | Going to do a 1-shot to get an estimate of the mix ratio. We want to monitor MC temperature (to tell when cooling stops), G2 pressure (to see how much mix we've pulled out), and Still temperature (to see when the Still runs dry). I'm logging pressures and temperatures, but we can only measure one temp at a time, so I'll switch back and forth between MC and Still thermometers. I will also change the thermometer calibration used on the vi each time I switch, so the logged temperatures will be accurate for both. We also want to keep the circulation rate constant during this since cooling power varies with the circulation rate, so I'll adjust the Still heater to keep P1 relatively constant. |
| 1019 | MC = 48.7 mK, G2=163.8 mbar, Still = 1.1 K / 0.036 mbar / 0 mW |
| 1026 | Close V13A and open V9 to start 1-shot test. G2 falls to 25.0 mbar before starting to rise. |
| 1037 | MC = 47.3 mK, G2=30.4 mbar, Still = 1.1 K / 0.036 mbar / 0 mW |
| 1045 | P1 → 0.34 mbar. Set Still heater = 0.2 mW, P1 → 0.36 mbar. |
| 1100 | MC = 40.0 mK, G2=46.9 mbar, Still = 1.0 K / 0.036 mbar / 0.2 mW |
| 1108 | G1 had been decreasing steadily, flattens out now. |
| 1113 | MC seems to have started increasing after reaching a minimum of 39 mK. At this time, G2=55.2 mbar. Assuming we were recovering pure 3He, that would mean we have recovered |
| 1116 | G1 starts to decrease again. |
| 1119 | MC = 42.9 mK, G2=60.2 mbar, Still = 1.0 K / 0.036 mbar / 0.2 mW. Still temp hasn't really changed. Either it remains full or has been empty this whole time. |
| 1140 | MC = 47.4 mK, G2=74.1 mbar, Still = 1.0 K / 0.034 mbar / 0.2 mW. Increase Still heat to 0.4 mW, P1 → 0.36 mbar |
| 1143 | P1 = 0.38 mbar, decrease Still heat to 0.3 mW. P1 → 0.36 mbar |
Above are the relevant data for the 1-shot taken today. The gaps and stray points in the MC data are due to switching to/from the Still thermometer. As mentioned above, 30.2 mbar55.2 mbar of mix were recovered between the beginning of the 1-shot and the time the MC temperature started to increase. If this was pure 3He, and if the temp increase indicated we had removed all of it from the fridge, we would have a mix ratio of 55.2/726.6 = 7.6%. This is considerably smaller than the 8/45=17.8% the fridge shipped with. These results can be compared to previous 1-shots taken on 2013/10/01, 2013/10/04, 2013/10/09, and 2013/10/11. Those previous tests also took 40-50 minutes until for the MC temp to increase but recovered 45-150 mbar during that time indicating mix ratios of 13-23%. Although the pressure and temperature trends measured today are qualitatively similar to previous results, the measured mix ratio seems low as dilution cooling should not be possible with a ratio less than ~7%, the dilute phase concentration.
| 1240 | MC = 93.5 mK, G2=114.7 mbar, Still = 0.87 K / 0.036 mbar / 0.3 mW. The Still is cooling a little bit. I guess now it's like a 1K pot, but with precooled 4he flowing into it from the MC. |
|---|---|
| 1300 | Still = 0.92 K / 0.38 mbar / 0.3 mW. Reduce Still heat to 0.2 mW. P1 → 0.32 mbar. Raise Still heat back to 0.3 mW. P1 → 0.36 mbar. |
| 1313 | MC = 138 mK, G2=138.6 mbar, Still = 0.85 K / 0.036 mbar / 0.3 mW. I was hoping the Still would heat up when it ran dry and we could get some sense of the liquid level in it. Maybe that would take a lot longer than I'm willing to wait. Let's get circulating again. |
| 1325 | Close V9, open V13A. Open V14 to let dump pressure in behind pump. G1/G2 → 431/397, P1 → 950 mbar. Whoa, maybe I should throttle it with V6. Close V14. |
| 1326 | Close V6 → 12.8% |
| 1330 | Open V14, P1 → > 1000 mbar. G1/G2 falling, so keep opening V6. At V6 = 16%, G1/G2 still falling, so open V6 → 100%. |
| 1335 | P1 falls into range while V6 is opening, but G1/G2 run away to >1 bar for a second before I close open V9 to let the pressure into the dump. G1/G2 = 678/620 mbar. This was a stupid way to do things. I thought the small about of pressure in the dump would be fine to let in through V14 and V6, like when we add the last bit of mix left in the dump to circulation. I should have just let it out from the dump, through trap 1 and throttled it with V12A/V13A. That would have kept all pressures below 1 bar. |
| 1351 | G1/G2 = 554/513 and falling, P1 = 0.034 mbar, MC = 975 mK |
| 1400 | Open V9 to try and let some dump contents out through trap 1. G1/G2 begin to fall, close V9. Evidently the dump is at < 500 mbar, so I can't let it out through V9, I guess I do have to go through V14 after all. |
| 1401 | Open V14 until P1 rises to ~200 mbar, then close it. Repeat this a few times. G1/G2 rise to ~925 mbar. Oops, that was a bit too fast. Open V9 again to let some mix back in the dump. Now that I suspect we've been losing 3He given the 1-shot results, I'm worried about any high-ish pressure. G1/G2 = 500/475 mbar and falling. |
| 1407 | G1/G2 = 458/424 mbar, P1 = 0.030 mbar, tower = 911 mK |
| 1418 | G1/G2 = 380/350 mbar and decreasing, tower = 878 mK. Open V14 for a couple seconds, until P1 ~ 200 mbar then close it. G1/G2 → 585/541 mbar |
| 1448 | G1/G2 = 354/328 mbar and decreasing, tower = 774 mK. Open V14 for a couple seconds, until P1 ~ 200 mbar then close it. G1/G2 → 474/438 mbar |
| 1544 | G1/G2 = 250/240 mbar and decreasing, tower = 725 mK. Open V14 for a couple seconds, until P1 ~ 200 mbar then close it. G1/G2 → 360/333 mbar |
| 1747 | G1/G2 = 205/193 mbar and decreasing, tower = 540 mK. Open V14 for a couple seconds, until P1 ~ 200 mbar then close it. G1/G2 → 319/298 mbar |
| 1810 | Fill LN2 cold trap full using 5L dewar. Large dewar is empty. |
| 1811 | G1/G2 = 268/251 mbar and decreasing, tower = 488 mK. Open V14 for a couple seconds, until P1 ~ 200 mbar then close it. G1/G2 → 360/354 mbar |