2021/04/30 (Friday)

Lab in-person: Zach
Virtual partner: Matt

Status	Run 74 in progress. Warming up after second occurrence of IVC leak during initial LHe transfer. Helium in Cryostat Vacuum Jacket. Mixture in dump.
0900	MC(Cernox) = 148.4 K rising at 5.5 K/hr, implies warming tau = 26.7 hr, predicted to reach dew point Sunday at 1:00 pm
0900	Recovery meter hasn't moved since last night. MB pressure low overnight, 113-119 mbar+1atm overnight
1000	MC(Cernox)/Sorb = 154/>250 K, IVC = 190 mbar
1335	MC(Cernox)/Sorb = 171 K, IVC = ? mbar - hard to read, the display is messed up at the moment
1514	Zach arrives at lab.
1520	Took out transfer stick and closed recovery valve.
1521	IVC = 190 mbar.
	We're trying some tests, curious as to whether we can identify the gas in the IVC. Since we have both a mechanical gauge and the composite Pfeiffer gauge on the manifold, we may be able to identify the gas because the Pfeiffer reading is gas-dependent but the mechanical gauge isn't. So we'll compare the two gauges for the gas that's in the IVC, then also compare the two gauges using pure He or pure N2 in the manifold.
1530	Pump out manifold with mechanical gauge, open back up to IVC, digital gauge = 160 mbar, mechanical gauge = 7inHg/28 = 250 mbar
1535	Pump out a little from the manifold, digital = 120 mbar, mechanical = 3inHg/28 = 107 mbar
	After this we repeated these measurements with different amounts of N2 or He in the manifold. But with helium, just a little gas, too little to even read on the mechanical gauge, causes the Pfeiffer gauge to max out at 1000 mbar. The various combinations are summarized below:

gas	mechanical [bar]	Pfeiffer [bar]
IVC	0.25	0.16
IVC	0.11	0.12
He	0.25	1
He	0.04	1
He	0.0	0.02
N2	0.0	0.054
N2	0.25	0.086
N2	0.07	0.074
He+N2	0.07	1

	Surprisingly the IVC gas behaves more like N2 than He. Of course, now that we are above 77K, there may be a significant amount of air in the IVC - we know it leaks in at the stripline elbow. Below 77K this would just be frozen on the IVC walls and not contribute to the pressure. The data suggests that maybe the IVC gas behavior is somewhere between that of pure He and pure N2. The final trial was to see what a mixture of He and N2 looks like. One tube-length of He was let into the manifold, then one tube length of N2 (that's more N2 than He because the N2 regulator is around 10 PSI, the He one around 4 PSI). The He made the Pfeiffer shoot to 1 bar, and the N2 did not as one may have expected cause it to fall again - it stayed at 1 bar. So, not sure we understand what's going on.
	Pfeiffer Gauge manual

Surprisingly the IVC gas behaves more like N2 than He. Of course, now that we are above 77K, there may be a significant amount of air in the IVC - we know it leaks in at the stripline elbow. Below 77K this would just be frozen on the IVC walls and not contribute to the pressure. The data suggests that maybe the IVC gas behavior is somewhere between that of pure He and pure N2.
The final trial was to see what a mixture of He and N2 looks like. One tube-length of He was let into the manifold, then one tube length of N2 (that's more N2 than He because the N2 regulator is around 10 PSI, the He one around 4 PSI). The He made the Pfeiffer shoot to 1 bar, and the N2 did not as one may have expected cause it to fall again - it stayed at 1 bar. So, not sure we understand what's going on.

Pfeiffer Gauge manual

1614	Begin pumping on IVC.
1624	Turbo on IVC = 0.25 ubar, IVC with turbo valved out for 1min = 4.0 ubar.
1645	Turbo on IVC = 30 nbar, IVC with turbo valved out for 1min = 0.34 ubar.
1700	MC(Cernox) = 183 K, so we want to fill the IVC with 183/300*28 = 17 InHg of N2, choose a slightly lower value of 16 InHg.
1705	Zach leaves lab.

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