2017/09/20 (Wednesday)

Previous Day

	Status: Tower installed and has passed electrical checks. IVC passed leak check. Pumped out IVC with turbo pump since Friday.
0910	Turbo = 16 nbar, IVC = 0.54 μbar.
0910	Trap 2 has 18.8 mbar of contaminants since yesterday's cryocleaning. Pump this out.
0915	Trap 1 has 10.2 mbar of contaminants since yesterday's cryocleaning. Pump this out.

Cryocleaning log
date	duration (minutes)	contaminants removed (mbar)
Sep 19	90	62.5
Sep 19	95	18.8
Sep 19	70	10.2

This looks good. Compare to Run 63.

1030	Raise main bath. We had some trouble - the cryostat was tilted, so the bottom of the IVC kept getting caught on the lower rim in the bath. We adjusted one of the cable lengths to make it more level. It took a while to get the screw holes lined up but we eventually managed.
1045	Open fridge lines up to Trap 1, which is cold in the LN2 bath. This to let the little bit of air in the fridge get cryopumped out.
1050	Make sure 1K Pot needle valve is closed, then pump out 1K Pot with scroll pump.
1110	Connect leak detector to IVC and isolate turbo pump. LD signal is 1.3 pbarL/s.
1115	Let mixture into fridge through Trap 1. 3He pump off, V9, V13a, V12a+speedi, V3, V1, condenser & still valves all open. LD signal does not increase.
1200	Begin pumping out main bath. P2 falls below 100 mbar quickly. Gauge on MB line falls to 2“Hg (absolute) after a couple minutes. P2 falls below 1 mbar after 5 minutes.
1210	Pressurize MB with He gas to 140 mbar above 1atm on G3. LD signal drifts up slowly, 2.8 pbarL/s after a few minutes - good! Better than Run 63 and previous.
note	He gas is left in the Vent volume, the auxiliary right volume, the auxiliary left (G3) volume, and the P2 volume.
1215	LD has crept up to 5.1 pbarL/s
1220	Let 5.4 mbar He exchange gas into IVC
1230	Begin transferring LN2 to main bath
1230	MC(Cernox) = 296.6 K, Sorb = >249 K (max), IVC = 5.4 mbar, G1 (fridge) = 644 mbar, Level resistor = 1.066 kΩ.
1240	MC(Cernox) = 293.2 K, Sorb = >249 K (max), IVC = 5.4 mbar, G1 (fridge) = 642 mbar, Level resistor = 1.092 kΩ.
1250	MC(Cernox) = 277.1 K, Sorb = >249 K (max), IVC = 4.0 mbar, G1 (fridge) = 641 mbar, Level resistor = 1.135 kΩ.
1300	MC(Cernox) = 258.7 K, Sorb = >249 K (max), IVC = 4.0 mbar, G1 (fridge) = 640 mbar, Level resistor = 1.169 kΩ.
1330	MC(Cernox) = 200.0 K, Sorb = >249 K (max), IVC = 2.5 mbar, G1 (fridge) = 636 mbar, Level resistor = 1.330 kΩ. Nearly full.
1335	MC(Cernox) = 188.5 K, Sorb = 235.6 K, IVC = 2.5 mbar, G1 (fridge) = 636 mbar, Level resistor = 1.347 kΩ. End transfer.
1445	MC(Cernox) = 115.0 K, Sorb = 156.0 K, IVC = 1.9 mbar, G1 (fridge) = 636 mbar. Fridge pressure has been flat since end of transfer.
1600	MC(Cernox) = 95.7 K, Sorb = 151.4 K, IVC = 1.6 mbar, G1 (fridge) = 637 mbar.
1630	MC(Cernox) = 91.8 K, Sorb = 150.8 K, IVC = 1.6 mbar, G1 (fridge) = 638 mbar.
1700	Perform 77K electrical check. Mostly things look OK. But cross-channel resistances, through the qBias lines, look strange and inconsistent:

Cross-channel continuity through qBias leads (all in nS)
	DIB1qI (qA)	DIB4qI (qB)	DIB1qO (qC)	DIB3qO (qD)	DIB4qO (qE)
DIB1qI (qA)	-	-	-	-	-
DIB4qI (qB)	13	-	-	-	-
DIB1qO (qC)	1.1	0.7	-	-	-
DIB3qO (qD)	7	7	1.0	-	-
DIB4qO (qE)	13	13	0.7	7	-
note qObias is pin 11, qIbias is pin 15 on I/O cable

At room temperature these all seemed to read 13 nS, which is simply the resistance of the two 40 MΩ bias resistors. Now several are much lower. qC is about 1 nS to all other channels. qD is 7 nS to all others except qC. qA, qB, qE are all still 13 nS with respect to one another.

It could be that some channels are now simply more isolated from the substrate than others. It would fit a model where qA, qB, qE are all still connected to the substrate by less then 3 MΩ, qD is isolated by around 70 MΩ, and qC is isolated by around 1 GΩ. Or could be that qC has a broken bond now. But we've never seen a bond go bad between room temperature and 77K.

Note that on September 8, qA, qB, and qE were shorted to one another before we fixed these shorts. Since these are now showing lower resistance than the others, could be that the shorts have returned since then.

1730	MC(Cernox) = 87.8 K, Sorb = 150.1 K, IVC = 1.6 mbar, G1 (fridge) = 639 mbar.

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