2012/08/23

0510	Fill N2 cold trap full.
0945	Fed Cricket 4 pellets.
0950	Filled LN2 cold trap.
1130	Internal leak check: 7E-7 cc/s. Calibration is fine. IVC leak rate pumping in parallel with turbo: 6.3E-7 cc/s. Leak rate with turbo isolated: 4.7E-6 cc/s.
1405	Even without isolating turbo pump, leak rate is 6.7E-7 mbar l/s. Value obtained for internal leak is correct, implying that there is no need for recalibration. Isolate leak checker and run regeneration cycle.
	Between around 0600 and 1100 today, the mixing chamber temperature increased from around 4.5 K to 6.0 K. The trend did not continue, which is a little puzzling. Isolate IVC to investigate.

1510	Run regeneration cycle again.
1615	Run regeneration cycle again.
1735	Run regeneration cycle again.
2330	Pumped mixture into dump, sealed it off, and cryopumped mixture from exhaust into cryopump. Cryopump was sealed off and left in liquid helium dewar.
	Sealed off fridge. Turned off and drained oil from He-3 pump. Oil was discoloured and smelt burnt. Ran pump for additional 10 seconds and drained remaining oil. Filled pump with 3 l of oil and turned it on.
	Cryocleaned He-3 pump exhaust through nitrogen cold trap 2 and valve 3, bypassing dump, for 10 minutes. Opened dump to He-3 pump exhaust and pumped mixture from cryopump to exhaust with He-3 pump.
2350	Mixing chamber temperature has oscillated around 6.07 K since 1405. It seems to indicate that there is no leak. Would we expect the temperature to rise due to heat load from conduction?
	Conducted quick helium leak check: 4.6E-6 mbar l/s, which would indicate that there is a leak. Could this be due to the large helium background in the room from cryopumping the mixture?