2014/08/31

1945	Fill N2 cold trap full.
	Fed Fish 74 & Fish 28.
1950	Evacute main bath. Background helium leak rate 9.3E-10 mbar l/s. Overpressurise main bath with He-4 gas. Helium leak rate increased to 1.2E-8 mbar l/s. This isn't an indication of a gross leak, but this is not a phantom or differential leak as the leak rate has not decreased. One possible explanation is an increased background helium leak rate. One way to check this is to increase the evacuate the main bath and try again. The leak rate shouldn't decrease too much if this is the new background leak rate.
1955	Evacuate main bath. Leak rate jumped all of sudden to 1.5E-6 mbar l/s, which would imply that there is a differential leak. This may not be something to worry about. Wait for leak rate to achieve new level.
2000	Background helium leak rate has dropped to 1.5E-8 mbar l/s. Time to try again.
2005	Overpressurise main bath with He-4 gas. Leak rate increases to 2.8E-8 mbar l/s. Just under what would be termed a gross leak. We face a choice: either drop the dewar and conduct another spray test, possibly changing the bottom indium seal; or risk it and cool down anyway. I think it would be more prudent to drop the dewar and conduct another spray test, perhaps replacing the bottom indium seal if nothing concrete is found. We have just about enough indium to do this.
2010	Taking a look at the indium we have left, it is the quality of it that could pose a problem. As liquid nitrogen is inexpensive, it may be worth risking it instead. Worst comes to worst, we lose one day… a holiday actually, and when phrased like that is an acceptable loss of time.
2030	Isolate leak checker and ressume evacuting IVC with turbo pump. Close condenser line speedivalve and gate vale.
	Fill IVC with 1.2 mbar of He-4 exchange gas.
2040	Commence nitrogen transfer. Mixing chamber temperature 297 K.
2245	Nitrogen level meter resistance 1.35 kΩ. Nitrogen transfer complete. Attach ping-pong ball. Mixing chamber temperature 188 K and falling.