2013/11/06

1130	Commence LN2 blow out. Leak check simultaneously performed with initial background rate of 3.7E-9 mbar*l/s.
	Whilst the blow out occurred a series of attempts to cryoclean the mixture occurred. These attempts are listed here.

Attempt 1: With an initial value of G2=680 mbar, cryocleaning commenced, immediately raising G2=983 mbar (G1=648 mbar). G1 dropped to 555 mbar when V12A is closed. When V12A is opened again, G1 goes up to 649 mbar and remains there, suggesting a possible block between coldtrap 1 and 13A. Pump back to dump.
Attempt 2: Before commencing cryocleaning: G1=0.4 mbar, G2= 677 mbar, P1=0.014 mbar. Once cleaning has been initiated, G1=646 mbar, G2= 982 mbar, P1= 1000 mbar. Close V14, resulting in G1=698 mbar, G2=638 mbar and P1=0.016 mbar. This seems to indicate that some mixture in G2 flowed through the safety valve into the dump and thus raised G1. Still no indication of pump affecting region of fridge after the cold trap. Pump back to dump.
Attempt 3: The purpose of this attempt was to try reducing the percent by which V6 is open, hopefully reducing the flow of mixture to the pump. Initially G1=0.7 mbar, G2=674 mbar, P1=0.014 mbar. Opening V4 results in G1=685 mbar, G2=674. Opening V14 resulted in a sudden flow of G1=581 mbar and G2=982 mbar. Note that V6 is still closed and thus there should be no mixture flowing to G2. This is a huge indicator that V6 is malfunctioning. This is further suggested by pumping to the dump, which can be done with V6 “closed”, since mixture is freely passing through the valve.
Attempt 4: This test is performed to verify that V6 is working improperly. Initially G1=17 mbar, G2=674 mbar, P1=0.02 mbar. Opening V4 (V12A open) results in G1=696 mbar, G2=674 mbar. Opening V13A results in G1=692 mbar, G2=629 mbar. These values seemed stable, possibly indicating that mixture is not being pumped into the dump? Opening V14 (with V6 closed) resulted in G1=635 mbar and G2=982 mbar. The results of attempt 3 have been repeated. The issue (or at least one issue), is due to V6 malfunctioning.

The issue with V6 has occurred before and is due to a screw inside the motorized part of the valve. To deal with this issue we opened up the motorized portion of V6 and found the screw. Pictures included below.

Figure 1

Figure 2

1224	Fill LN2 cold trap full.
1310	LN2 blow out ended. Pull out transfer stick and seal off main bath. Leak check rate has raised slowly to 4.0E-9 mbar*l/s, with no peaks or any indication of a leak. Pump on main bath with He-4 pump.
1600	Valve V6 is very tight, but managed to close it manually. Spoke to Ron in mechanical workshop about replacement set screw, and he suggested replacing it with a socket head screw and drilling a larger hole. Gearbox removed from motor and given to Ron. He will work on the modifications tomorrow.
	We can either delay the helium transfer until tomorrow so that we can perform a throughput test, or perform the transfer today and forego the throughput test. In the interest of saving time, we shall abandon the throughput test and continue with the transfer. Even if we are unable to get to a suitable base temperature this run, we should be able to take the ionisation data required as long as the base temperature is around 100 mK. Before condensing the mixture tomorrow, we should cryoclean it once we receive the modified gearbox and shaft.
1635	IVC pressure 1.6E-6 mbar. Fill IVC with 0.54 mbar He-4 exchange gas.
1715	Start LHe transfer.
1810	Conduct electrical check at 86 K: looks fine.
2145	Mixing chamber temperature 10 K; start evacuating IVC with turbo pump.