2015/03/25
| 0904 | G2 = 664 mbar with V9 open (dump pressure). This is significantly lower than yesterday, when it was 700 mbar. G2 funniness? or is mixture hiding somewhere? |
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| Opened V4 to see dump pressure on G1. G2 falls to 662 mbar, G1 reads 717 mbar! So who knows. Closed V4 and opened V5 to evacuate G1 volume back to dump. | |
| 0925 | Fill LN2 cold trap full. Open gate valve and V6 to pump remaining mixture from fridge lines to the dump. This increased G2 to 710. So yes, it was hiding in the fridge. Ok then. |
| This dump pressure is higher than yesterday's dump pressure. But note that the barometric pressure is lower today… |
| yesterday morning | barometric pressure = 30.16 “Hg | dump@G2 = 700 mbar |
| this morning | barometric pressure = 29.82 “Hg | dump@G2 = 710 mbar |
| change | barometric pressure -11.5 mbar | dump@G2 +10 mbar |
This is consistent with a gauge that actually is measuring differential pressure (and converting to absolute pressure). If this is true, then the pressure reading can be corrected based on the average barometric pressure (29.92 inHg) and the current barometric pressure Pbar as follows:
Ptrue[mbar] = Pdisplay[mbar] + ( Pbar[inHg] - 29.92 ) * 33.86
Local barometric pressure can be reported as either the raw pressure read at the station or the sea level pressure, i.e. the local pressure corrected for the elevation of the station. Here forward I use the sea-level pressure. This can be found in the “weather history” section of Weather Underground.
| 0945 | Begin procedure to ADD MORE 4He TO MIX. G2 reading 711.3 mbar at the beginning of procedure |
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| 1033 | 4He added to mix until G2 pressure reads 753.2. Close V5 and V9 and open cold trap 1 to scroll pump, to pump out excess 4He and in preparation for a cold trap cleaning. |
Procedure for adding 4He to mixture
- Secure mixture: Pump all mixture from GHS lines to dump. The only places there should be mixture are the dump, the G2 volume, and possibly the fridge. Close all valves.
- Measure the amount in the dump: Open V9 and note the pressure on G2. Choose a target value based on the amount of mixture you want to add.
- Choose a cold trap. Trap should be at 77K. Open V11 and V12+speedivalve. G1 should be low.
- Run a plastic tube from He cylinder to vent port. Let helium be flowing from cylinder when tube is attached to vent port. Open vent port valve.
- Close valve at cylinder then pump out tube using pot pump through vent port valve, V2a, and V5a. Then close V2a.
- Let more helium into tube, then repeat step 5. Then open valves at cylinder and leave the tube pressurized.
- Open then immediately close V7. This should let around 80-120 mbar into trap, read at G1. Allow reading to stabilize.
- Pump trap contents to dump through V5. Wait until G1 stops decreasing, at around 4 mbar. Then close V5.
- Note new pressure on G2 (dump). A 100 mbar increase at G1 (trap) will correspond to about a 6 mbar increase at G2 (dump). (This suggests that the effective volume of the trap is a little less than 1 liter.)
- Iterate 7-9 until the target is reached at G2. Note that the increase in the dump contents may be underestimated because the new gas may be colder than room temperature. After fully warming the dump increase may be as much as 10% larger. (It may depend on how much mixture was in the dump at the beginning of the procedure.)
| 1045 | Commence cryocleaning mixture through cold trap 2. |
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| Fill LN2 cold trap full. | |
| 1145 | Commence condensation procedure through cold trap 1. |
| 1300 | Commence circulation through cold trap 1. |
| 1320 | V6 open all the way. Commence adding remaining mixture from dump through V14. |
| 1326 | MC = 677 mK, Still = 920 mK, G1/G2/P1 = 169 / 186 / 0.22 mbar, 1KPot = 1.79 K / 80 mbar. Continuing to open/close V14. |
| 1330 | Leaving V14 open |
| 1332 | MC = 517 mK, Still = 945 mK, G1/G2/P1 = 127 / 144 / 6 mbar, 1KPot = 1.80 / 100 mbar |
| 1348 | MC = 455 mK, Still = 991 mK, G1/G2/P1 = 154 / 160 / 1.1 mbar, 1KPot = 1.80 / 110 mbar |
| 1400 | MC = 406 mK, Still = 1.01 K, G1/G2/P1 = 158 / 161 / 0.60 mbar, 1KPot = 1.80 / 110 mbar |
| 1402 | Close V14 |
| 1408 | Adjust needle valve to reduce 1KPot temp a bit |
| 1416 | MC = 485 mK, Still = 881 mK, G1/G2/P1 = 102 / 109 / 0.18 mbar, 1KPot = 1.60 / 7.0 mbar |
| 1426 | MC = 514 mK, Still = 880 mK, G1/G2/P1 = 107 / 113 / 0.19 mbar, 1KPot = 1.60 / 7.0 mbar |
| 1432 | Turn on still heater. 0.5 mW. |
| 1442 | Still heat 2.0 mW, Still 917 mK, MC 454 mK, 1KPot 1.60 K, G1=118 mbar, G2=126 mbar, P1=0.22 mbar, P2=7.0 mbar |
| 1452 | Still heat 4.0 mW, Still 957 mK, MC 413 mK, 1KPot 1.60 K, G1=124 mbar, G2=132 mbar, P1=0.24 mbar, P2=7.0 mbar |
| 1505 | Still heat 8.0 mW, Still 1.05 K, MC 354 mK, 1KPot 1.60 K, G1=126 mbar, G2=137 mbar, P1=0.30 mbar, P2=7.0 mbar |
| 1514 | Still heat 12.0 mW, Still 1.11 K, MC 329 mK, 1KPot 1.60 K, G1=136 mbar, G2=149 mbar, P1=0.34 mbar, P2=7.0 mbar |
| 1523 | Still heat 16.0 mW, Still 1.17 K, MC 318 mK, 1KPot 1.61 K, G1=142 mbar, G2=157 mbar, P1=0.38 mbar, P2=8.0 mbar |
| 1534 | 1KPot crept up a bit, to 1.63 K / 11 mbar, so closed the needle valve slightly. |
| 1538 | Preparing for transfer. Bath down to 6.3%. |
| 1538 | Still heat 20.0 mW, Still 1.16 K, MC 304 mK, 1KPot 1.62 K, G1=144 mbar, G2=164 mbar, P1=0.40 mbar, P2=8.5 mbar |
| 1548 | Still heat 24.0 mW, Still 1.20 K, MC 300 mK, 1KPot 1.63 K, G1=154 mbar, G2=176 mbar, P1=0.45 mbar, P2=9.5 mbar |
| 1559 | Still heat 28.0 mW, Still 1.23 K, MC 296 mK, 1KPot 1.63 K, G1=173 mbar, G2=194 mbar, P1=0.50 mbar, P2=10 mbar |
| 1615 | Commence LHe transfer (5.3%). |
| 1619 | During transfer 1K Pot temperature rises and P2 falls; open needle valve more. After this 1K Pot settled to 1.65 K and P2=11.0 mbar. G1 and G2 also rise above 300 mbar. To combat this, lower still heater to 15 mW. |
| 1630 | Fill LN2 cold trap full. |
| 1632 | Still heat 15.0 mW, Still 1.26 mK, MC 290 mK, 1KPot 1.64 K, G1=286 mbar, G2=285 mbar, P1=0.56 mbar, P2=11.0 mbar. |
| 1636 | Still heat 15.0 mW, MC 286 mK is new lowest MC temperature reached. Some oscillations near 290 mK. |
| 1650 | Still heat 10.0 mW, Still 1.26 mK, MC 295 mK, 1KPot 1.61 K, G1=164 mbar, G2=173 mbar, P1=0.32 mbar, P2=9.0 mbar. |
| After several minutes, G1 and G2 pressures seem to have stabilized at around values given above. | |
| 1710 | Cease LHe transfer (95.9%). With transfer complete, still heat 10.0 mW, Still 1.07 mK, MC 296 mK, 1KPot 1.59 K, G1=121 mbar, G2=134 mbar, P1=0.30 mbar, P2=7.5 mbar. Lower still heater to 5 mW. |
| 1731 | Still heat 5.0 mW, Still 0.973 mK, MC 350 mK and still rising, 1KPot 1.56 K, G1=112 mbar, G2=119 mbar, P1=0.22 mbar, P2=6.0 mbar. Although this setup might eventually result in stability, raise still heater back to 10.0 mW. |
| 1835 | MC 321mK and rising steadily. Reduce still heater to 8.0mW. |
| 1910 | MC 337mK and still rising. Reduce still heater to 5.0mW. |
| 1920 | MC 355mK and still rising. Pump to dump. Stop pumping on 1K Pot. |