2018/04/25 (Wednesday)

Previous Day

	LN2 transfer ended yesterday evening, cool to 77K overnight.
0931	MC(Cernox) = 77.2 K, Sorb = 127.5 K, IVC = 1.4 mbar, G1 (fridge) = 208 mbar, Level resistor = 1.210 kΩ.
0945	Start pumping out IVC
1041	Electrical check at 77K. DIB3 QET A short to ground is back, but at 4.9 kΩ as opposed to 380 Ω as before. Several other channels also see ground at ~2-40 MΩ, but only when measuring from GDN→channel, not the reverse. This sucks.
1120	Turbo on IVC = 4 nbar. Leak on IVC with turbo pumping = 43 pbarL/s. With turbo valved out, IVC = 100 nbar. IVC leak = 544 pbarL/s
1130	Begin blowing out LN2 from main bath IVC leak = 540 pbarL/s, Main bath = 315 mbar above 1 atm
1132	IVC leak = 524 pbarL/s, Main bath = 280 mbar above 1 atm
1134	IVC leak = 514 pbarL/s, Main bath = 220 mbar above 1 atm
	pressure started falling right away, must not have been much LN2 left in the bath.
1136	IVC leak = 514 pbarL/s, Main bath = 200 mbar above 1 atm
1139	IVC leak = 519 pbarL/s, Main bath = 197 mbar above 1 atm
1140	Forgot to push transfer tube all the way into funnel. Did that just now - bath pressure goes way up.
1141	IVC leak = 519 pbarL/s, Main bath = 403 mbar above 1 atm
1145	IVC leak = 491 pbarL/s, Main bath = 416 mbar above 1 atm
1150	IVC leak = 463 pbarL/s, Main bath = 419 mbar above 1 atm
1155	IVC leak = 446 pbarL/s, Main bath = 345 mbar above 1 atm. Pressure just beginning to fall.
1157	IVC leak = 443 pbarL/s, Main bath = 185 mbar above 1 atm
1200	IVC leak = 441 pbarL/s, Main bath = 152 mbar above 1 atm
1202	IVC leak = 445 pbarL/s, Main bath = 151 mbar above 1 atm. Stop pressurizing main bath.
1235	Begin pumping out main bath with scroll pump
1255	Main bath = 0.2 mbar on P2, all the LN2 is out.
1255	Mini-throughput test: isolate LN2 Trap 2, close V3, turn on 3He pump and open V9, open V6 to 12.8%. This pumps out the still side of the fridge, we can watch G1 to see if the condenser side falls.
1300	Still has fallen to 0.04 mbar but condenser is flat at 204.7 mbar. ~~Looks like a blockage.~~ - no, the still gate valve was closed… open it now… and it looks like the condenser is falling. Good. Starting at 200 mbar, condenser falling at 8 mbar/min.
	Throughput test procedure, Cold Trap 2:

All mixture in dump, LN2 traps cold, condenser & still valves open (3He pump on - optional)
Open V9, V13b, V12b+speedivalve, V3. Wait for G1 to be close to G2.
Close V12b+speedivalve and V3, open V1
monitor G1

1310	Perform mixture throughput test at MC = 77 K using above procedure. Let G1 rise to 568 mbar before Step 3, then it falls to 68 mbar, then rises. Throughput 43.7 mbar/min, looks good. Compare with 48.0 mbar on April 17.
	Looking back there seems to be a pattern: we avoid blockages if we cryoclean mixture, then let it into the fridge, then do the LN2 transfer all in the same day. If we cryoclean then let it sit overnight, then do LN2 first thing in the morning, we're likely to get a blockage.
1315	DIB3 QET return A short to chassis = 5.25 kΩ, up from 4.2 for most of today.
1320	Pressurize main bath with N2 (why waste helium) to 190 mbar above 1atm.
1335	Let about 0.04 bar He gas into IVC. MC temperature rising 0.1 K/min. Short resistance is going up slightly.
1345	MC(Cernox) = 78.9 K, Short = 5.30 kΩ
1400	MC(Cernox) = 80.1 K, Short = 5.33 kΩ
1405	Let N2 into the IVC up to about 0.24 bar
1415	MC(Cernox) = 80.7 K, Short = 5.35 kΩ
1430	MC(Cernox) = 81.1 K, Sorb = 149.2 K, main bath outer surface = 23.3 C, Short = 5.38 kΩ
1435	Let 26 plastic-hose-lengths of N2 into cryostat vacuum jacket (equivalent of about 200 mbar at pump manifold). Vacuum jacket pressure = 8.6 mbar. Notice that main bath pressure increases.
1505	MC(Cernox) = 83.1 K, Sorb = 162.8 K, main bath outer surface = 21.6 C, Short = 5.48 kΩ
1525	MC(Cernox) = 85.9 K, Sorb = 176.1 K, main bath outer surface = 21.0 C, Short = 5.60 kΩ
1615	MC(Cernox) = 95.5 K, Sorb = 205.9 K, main bath outer surface = 20.4 C, Short = 5.90 kΩ
1635	MC(Cernox) = 99.2 K, Sorb = 214.8 K, main bath outer surface = 20.3 C, Short = 6.15 kΩ
1705	MC(Cernox) = 105.2 K, Sorb = 228.3 K, main bath outer surface = 20.3 C, Short = 6.24 kΩ
1745	MC(Cernox) = 113.3 K, Sorb = 244.4 K, main bath outer surface = 20.2 C, Short = 6.54 kΩ
	switch meter to 200kΩ range to monitor remotely - now reads 6.7 kΩ
1815	MC(Cernox) = 118.9 K, Short = 6.9 kΩ
1845	MC(Cernox) = 124.4 K, Short = 7.1 kΩ
2015	MC(Cernox) = 140.1 K, Short = 7.7 kΩ
2050	MC(Cernox) = 145.7 K, Short = 7.9 kΩ
2200	MC(Cernox) = 156.4 K, Short = 8.3 kΩ
0410	MC(Cernox) = 201.0 K, Short > 200 kΩ

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