2013/10/20

0100	Mixing chamber temperature plateaued at 61.1 mK. Reduced 1 K pot temperature to 1.65 K - isn't holding particularly steady, but good enough. It seems as though 1 K pot pump requires service. Mixing chamber temperature decreased to 60.3 mK. This is probably the best we can do. Having said that, still pressure is 50 μbar, which would imply that still may be running dry. Perhaps adding more mixture would help.
	First things first, however. Let's check if applying heat to the still has any effect. Turn on still heater, power 1 mW.
0155	Mixing chamber temperature did decrease a little when still heater was turned on, before rising again. Mixing chamber temperature feel by less than 0.1 mK, so no cause for celebration.
	Still heater power: 1.0 mW Still pressure: 70 ± 2.5 μbar Mixing chamber temperature: 63.3 ± 0.05 mK Still thermometer: 4.54 ± 0.01 kΩ Cold plate thermometer: 17.2 ± 0.1 kΩ
0205	Turn off still heater.
0300	Mixing chamber temperature appears to have stabilised at a slightly higher value of 60.7 mK. Perhaps waiting longer would help, but temperature history shows that it has plateaued.
	Still heater power: 0.0 mW Still pressure: 55 ± 2.5 μbar Mixing chamber temperature: 60.7 ± 0.05 mK Still thermometer: 4.60 ± 0.01 kΩ Cold plate thermometer: 17.6 ± 0.1 kΩ
	Introduce a little mixture into the fridge via valve V14 on IGH (open for around 2 seconds). Wait for mixing chamber to reach new base temperature.
0415	Mixing chamber temperature appears to have plateaued at 59.9 mK and still pressure is 80 μbar. Still is a little cooler at 4.63 ± 0.01 kΩ, although cold plate isn't different at 17.7 ± 0.1 kΩ. It appears as though the still may have been running dry, hence the reason for the poor base temperature. A choice is apparent: one could add more mixture to the fridge to see if this improves matters; or one could commence a single-shot test to see if there is any evidence of incorrect He-3 concentration in the mixture.
	Adding more mixture to the fridge would be interesting. Keep valve V14 on IGH open for longer (10 seconds). Wait for mixing chamber to cool to new base temperature.
0550	Mixing chamber temperature appears to have stabilised at 60.2 mK.
	Commence single-shot test. Approximately 30 seconds pass before mixing chamber temperature starts to decrease.
0655	Cease single-shot test. No evidence of double-dip at end, which implies that phase boundary probably lay in mixing chamber. Kink seen at end in figure below is due to sudden drop in still pressure. This was rectified by increasing still heater power.

0700	Stop 1 K pot.
	Start pumping mixture into dump from both sides of the fridge.
0710	Fill N2 cold trap full.
2030	Fill N2 cold trap full.
	Turn on still heater (power 10 mW) to aid mixture recovery.