2015/04/03
| 0040 | Fill N2 cold trap full. |
|---|---|
| 0807 | Fill N2 cold trap full. Mixing chamber stable at 23 mK, G1= 65 mbar, G2=67 mbar, P1=95 mbar, 1K Pot at 1.67 K, and P2=12 mbar. |
| 0840 | Fill N2 trap full again because I didn't read this. Note to self: I'm not always the first one here (MF) |
| At around 6:00 am there was an increase in G1 and G2 for some reason of about 5 mbar. There were some accompanying wiggles in the MC temperature but only on the +/- 0.1 mK scale. | |
| 0845 | MC = 23.0 mK, G1/G2 = 66/67 mbar, Still = 0.10 mbar, 1K Pot = 1.67 K / 12 mbar |
| 0845 | main bath = 38.0 % |
| 0845 | Begin more aggressive cooling power test. Set MC heater to 10 μW. (No still heating.) |
| 0851 | two peaks in MC temperature, 54 mK and 52 mK |
| 0856 | MC temperature settles around 47 mK |
| 0857 | Set MC heater to 20 μW |
| 0902 | MC temperature at 56 mK, increasing steadily |
| 0911 | MC settling near 59 mK. Set MC heater to 30 μW. |
| 0926 | MC settling near 88 mK. Set MC heater to 40 μW. |
| 0935 | MC peak at 100 mK, then falls again |
| 0950 | MC settles back down to near 87 mK. Set MC heater to 50 μW. |
| 0958 | MC settling near 104 mK. Set MC heater to 60 μW. MC peaks to 108 mK then falls again. |
| 1006 | Dips to 103 mK then rises again |
| 1007 | Peaks to 107 mK then falls again |
| 1022 | MC settling to near 102 mK. Set MC heater to 70 μW |
| 1049 | MC settling to near 113 mK. Set MC heater to 80 μW |
| 1109 | MC settling to near 116 mK. Set MC heater to 90 μW |
| 1125 | MC settling to near 120 mK. Set MC heater to 100 μW |
| 1145 | MC = 131 mK, flattish |
This is a pretty quick test to get rough results for a cooling power curve. MC temperature does a bit of wiggling at each change of heater setting, and I haven't necessarily waited long enough at each step to let it settle. Table below includes total time at each setting and how long I let it sit at a somewhat stable temperature before calling it.
| MC heater power (μW) | Stablish temperature (mK) | Total time at this power (min) | Time in “metastable” state (min) |
|---|---|---|---|
| 0 | 23.0 | >1000 | >1000 |
| 10 | 47 | 12 | 2 |
| 20 | 59 | 14 | 3 |
| 30 | 88 | 15 | 5 |
| 40 | 87 | 24 | 3 |
| 50 | 104 | 8 | 4 |
| 60 | 102 | 24 | 5 |
| 70 | 113 | 27 | 4 |
| 80 | 116 | 20 | 5 |
| 90 | 120 | 16 | 5 |
| 100 | 131 | 20 | 5 |
Looks like at 100 mK the cooling power is around 55 μW.
| 1306 | MC at 123 mK |
|---|---|
| 1325 | MC = 122 mK / 100 μW, G1/G2 = 87/86 mbar, Still = 0.14 mbar, 1KPot = 1.68 K / 12 mbar |
| MC heat has been at 100 μW and pretty stable for about 20 minutes. Start applying still heat to see if it can cool further. | |
| 1326 | MC = 122 mK. Apply 2 mW to still |
| 1341 | MC = 113 mK. Apply 4 mW to still |
| 1351 | MC = 108 mK. Apply 6 mW to still |
| 1400 | MC = 105 mK. Apply 8 mW to still |
| 1410 | MC = 102 mK. Apply 10 mW to still |
| 1427 | MC = 101 mK. Apply 12 mW to still |
| 1438 | no improvement, return still to 10 mW |
| Begin reducing MC heat (cooling curve in other direction with attempted optimal still heat) | |
| 1439 | MC = 101 mK. Reduce MC to 80 μW |
| 1452 | MC = 96 mK. Try reducing still heat - MC gets warmer, return still to 10 mW |
| 1503 | MC = 96 mK. Reduce MC to 60 μW |
| 1530 | MC temperature got a bit squirrely, looks like a ball bouncing down stairs. Finally settles down. |
| 1531 | MC = 86 mK |
| 1532 | try reducing still heater to 8 mW. MC temp goes up. |
| 1536 | return still to 10 mW. |
| 1542 | MC = 87 mK. Reduce MC heater to 40 μW |
| 1558 | MC = 74 mK. Reduce MC heater to 20 μW |
| 1609 | Reduced still heat to 8 mW: MC cools a bit |
| 1630 | Begin LHe transfer (26.5%). |
| 1635 | Reduced still heat to 6 mW: very little change. |
| 1638 | MC = 57 mK. Reduce MC heater to 0 |
| 1649 | Coldplate temperature = 117 mK |
| 1650 | Fill LN2 cold trap full. |
| 1700 | End LHe transfer (61.2%). |
| 1707 | MC = 24.0 mK, flat. Reduce still heat to 3 mW |
| 1711 | MC = 23.4 mK. Reduce still heat to 1 mW |
| 1715 | MC = 23.4 mK. Turn off still heat. |
| 1720 | MC = 23.3 mK |
Cooling power test with still heat applied:
| MC heater power (μW) | Final MC temperature (mK) | Approx. optimal still heater power (mW) |
|---|---|---|
| 100 | 101 | 10 |
| 80 | 96 | 10 |
| 60 | 86 | 10 |
| 40 | 74 | 10 |
| 20 | 57 | 6 |
| 0 | 23.3 | 0 |
| 1721 | MC = 23.3 mK, G1/G2 = 89/84 mbar, Still = 0.095 mbar, 1K Pot = 1.63 K / 9 mbar |
|---|---|
| 1731 | MC = 22.9 mK |
| 1734 | MC = 22.8 mK |
- Note that at 100 mK the cooling power is about 100 μW - as per factory specs!
- If we fit the curve to a square root, it crosses the 0 mK line at about -7 μW – this suggests a residual heat load of about 7 μW