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2014/08/14

0900 Change excitation to mixing chamber thermometer from 2uV to 2mV. Temperature still oscillating between ~990mK and ~910mK. Mixing chamber temperature and 1K Pot temperature seem unrelated; 1K Pot steady at ~1.53K while mixing chamber oscillates.
0910 Open 1K Pot needle valve to warm up 1K Pot. Settle at 1.71K. G1 and G2 increase to 141mbar and 139mbar, respectively. Mixing chamber temperature still oscillates.
0950 G1/G2 stable at 146/144mbar, respectively, but mixing chamber still oscillating up to values of 1.01K.
1030 Begin looking for ground loops, which could be warming up fridge. Temperatures/pressures in following table:
G1 (mbar) G2 (mbar) P1 (mbar) P2 (mbar) 1K Pot Temperature (K) Mixing Chamber Temperature (mK)
Current 154.9 152.6 0.26 75 1.761 953
Unplug Turbo Pump
Turn off He level meter
Turn off lights 		151 149.0 - - 1.753 861
Unplug thermometer 155 154 - - 1.750 940 (after plugging thermometer back in)
No relation between electronics and mixing chamber temperature found.
1040 Fill LN2 cold trap full.
1205 Pump mixture to dump. G1: 155.3mbar, G2: 154.5mbar, 1K Pot Temperature: 1.752K.
1230 Commence LHe transfer (6.0%).
1320 Complete LHe transfer (93.0%).
1423 Close V1.
1433 G1: .9mbar, G2: 598.7mbar, P1: .04mbar. Open valve to pump potentially leftover mixture from cold trap 2 into dump. G1 increase to 2.9mbar.
1445 Close 1K Pot speedivalve. Turn on still and mixing chamber heaters to speed mixture recovery.
1515 Begin pumping on IVC with turbopump. Pressure reads 4.6E-3mbar, but is most likely lower.
1605 G1: .7mbar, G2: 709.5mbar, P1: .045mbar. Close gate valve and condenser speedivalve to protect whatever mixture may still be in fridge lines.
P1 drops to .015mbar. Close V6 and turn off heaters.
Switch to high-temperature thermometer. Fridge temperature jumps from ~1.7K to >4.2K. V6 completely closed; no increase in P1, so no indication of leak in fridge lines.
1610 G1: .8mbar, G2: 710.2mbar. Mixture “fully” in dump. Close all valves on IGH. Pull out nitrogen cold trap 1 and helium cold trap for cleaning.
1620 Commence first round of cold trap cleaning.
1700 Finish first round.
1800 Finish second round.
1835 Finish final round.
1900 Replace cold traps.
1915 Fill LN2 cold trap full. Despite pumping out of cold traps, G1 is still suspiciously high at 1.5mbar. G2: 711.1mbar (no significant increase since isolation of dump), P1: .017mbar. Mixing chamber temperature of 6.95K.
1920 Isolate He4 rotary pump.
1930 No change in G1 after isolation. Commence cryocleaning mixture through cold trap 1.