2019/11/01 (Friday)

Previous Day

	Status: At 77K discovered IVC leak near bottom of IVC. Warming now to check indium seal. Working toward 2nd attempt at Run 71 cooldown.
0925	MC(Cernox) = 282.5 K
0930	Pump out IVC .
1000	Turn off MC and Still heaters.
1020	MC(Cernox) = 282.7 K
1025	Lower main bath
1030	Leak detector on IVC = 29 pbarL/s
1030	Squirt helium around middle IVC seal, bottom stripline tube seal, lower IVC seal. No change in signal.
1045	Try loosening all the screws on the bottom seal, then squirt helium at it again. Still no detectable leak. Thought about trying to cool it down with LN2, but probably would have to cool it more than I'd like.
1055	Stop leak detector, erect clean tent, fill IVC with N2.
1120	After opening IVC, inspect bottom flange. In several places scratches were visible extending from the inner edge to a screw hole. Polished these areas with Scotch Brite, being careful to rub back and forth tangential to the circle, no inward/outward polishing. Cleaned these areas with methanol and a wipe. With just a little polishing the scratches disappeared.
1130	Also polish the bottom piece flange a little with 1500 grit sandpaper and lightly with Scotch Brite
1200	Put a new indium o-ring on bottom flange piece and install, tighten screws most of the way
1205	Start pumping IVC with scroll pump
1210	Retighten all screws on all three other in-bath IVC flanges - top, middle, and stripline tube. They all seemed quite tight already, couldn't turn any more than a small amount. A few are starting to have stripped heads, but they still seemed to be rather tight.
1215	Switch to Turbo to pump out IVC
1300	Turbo on IVC = 400 nbar
1310	LD on IVC = 18 pbarL/s Squirt helium at top of stripline tube and bottom IVC seal. No leak seen.
1420	Check fridge pressures: LHe trap/Condenser/Still = 0.1/0.1/0.015 mbar (very low). Pump out with scroll pump.
1450	Tighten IVC screws one more time, then raise main bath. Adjust fridge insert mount brackets slightly to align fridge/rack/main bath better.
1455	Turbo on IVC = 1.2 μbar, IVC = 5.4 μbar with Turbo valved out for a few minutes. Stop pumping out IVC to pump out cryostat vacuum jacket.
1505	Cryostat vacuum jacket = 6.3 mbar. Pump out with scroll pump.
1520	Start pumping cryostat vacuum jacket with turbo pump
1545	Turbo on cryostat vacuum jacket = 1.4 μbar, cryostat vacuum jacket = 74 μbar with turbo valved out for a two minutes
1635	Turbo on cryostat vacuum jacket = 1.0 μbar, cryostat vacuum jacket = 46 μbar with turbo valved out for a two minutes Stop pumping cryostat vacuum jacket.
1645	IVC = 40 μbar. Start pumping IVC with turbo pump.

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