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2012/07/08

0150 Results of Tc measurements for DIB 1 in Table 1. Values taken from mixing chamber thermometer, so actual tower temperature may be higher. It appears that our base temperature does indeed lie above the Tcs. If we can reduce the base temperature to 70 mK, we are in business! Trouble is, how to get there…
Although it may be a little early to tell, if this crystal is similar to 3“ iZIPs, Side 2's Tcs probably lie under Side 1's.
Table 1: Tc Measurements for DIB 1.
DIB Channel Side & Channel Tc while cooling [mK] Tc while warming up [mK]
A Side 1 B 82.9 81.6
B Side 1 F 83.1 82.0
C Side 1 C 83.6 81.8
D Side 2 D 77.8 76.9
0430 As suspected, the cooling power is pathetic. This may work in our favour: the temperature drops below 70 mK for 158 minutes. It would be possible to take data during this time.
Possible plan of action: warm up to 4.2 K and clean cold traps. Then recondense and recirculate. If this does not result in a lower base temperature, we should lock all the SQUIDs and take data using the single-shot technique.
Figure 1: Dump Pressure and Mixing Chamber Temperature as a function of Time during Single-Shot.
0620 Fill N2 cold trap full.
1400 Fed Cricket and Livingston.
1415 Filled LN2 cold trap.
1517 Closed 1 K pot speedivalve. Closed V4A.
1540 Opened V5. Upon inspecting the rate of temperature increase of the mixing chamber, it seems that around 1400 it leveled off around 675 mK. Also, around this same time the rate of pressure increase in G2 also slowed down.
1613 Opening V5 has resulted in the mixing chamber temperature to slowly decrease. I think this makes sense because we're pulling out the warm mixture from another avenue, thus initially lowering the temperature.
1720 Mixing chamber hti low of 591 mK. Starting to show signs of increase in temperature again.
1740 Turn on mixing chamber heater and power to 2 mW to aid warm up.
1745 Begin LHe transfer (34.3%).
1815 Turn up mixing chamber heater to 20 mW.
1820 Cease liquid helium transfer. Helium liquid level 93.6%.
1835 Mixing chamber temperature >6 K, pressure in dump 557 mbar. Turn off mixing chamber heater.
1915 Mixing chamber temperature 3.9 K, pressur ein dump 582 mbar. Turn on mixing chamber heater, power 5 mW.
2300 Fill N2 cold trap full.
Not convinced all mixture is out of fridge. It may be best to wait until morning. Shall leave still heater on overnight as mixing chamber temperature appears to have stabilised at 6.2 K.