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2018/04/20 (Friday)

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LN2 transfer yesterday. Mixture in fridge.
0710 MC(Cernox) = 77.2 K, Level resistor = 1.250 kΩ.
0935 MC(Cernox) = 77.3 K, Sorb = 122.6 K, IVC = 1.6 mbar, G1 (fridge) = 597 mbar, Level resistor = 1.238 kΩ.
0940 Begin pumping out IVC, first with scroll pump then turbo pump.
0955 Start leak detector on IVC while turbo still pumping. Background 500 pbarL/s, falling. Turbo 8.6 nbar.
1000 Leak 100 pbarL/s, falling. Turbo 6.3 nbar. With turbo valved out leak is around 800 pbarL/s.
1018 Electrical check: DIB4 PB-GND = 6 MΩ, PC-GND = 12 nS, DIB1 PB-GND = 18 nS, PC-GND = 5 nS, DIB3 Feedback C = ~500 k (unstable), QETA-ret = 630 Ω, QETAret-GND = 380 Ω. Some DIB3 issues went away by reseating the cable. This DIB3PA ret short to ground seems to be the main issue, the other channels see ground through it.
we can't run with this short. Gotta warm up again.
1045 Leak 30 pbarL/s, falling. Turbo 4.6 nbar. With turbo valved out leak is around 310 pbarL/s.
1055 IVC leak = 320 pbarL/s
1100 Begin blowing out LN2 from main bath
IVC leak = 308 pbarL/s, Main bath = 420 mbar above 1 atm
1105 IVC leak = 295 pbarL/s, Main bath = 432 mbar above 1 atm
1110 IVC leak = 282 pbarL/s, Main bath = 415 mbar above 1 atm
1115 IVC leak = 275 pbarL/s, Main bath = 412 mbar above 1 atm
1120 IVC leak = 264 pbarL/s, Main bath = 409 mbar above 1 atm
1125 IVC leak = 265 pbarL/s, Main bath = 406 mbar above 1 atm
1130 IVC leak = 251 pbarL/s, Main bath = 417 mbar above 1 atm
1130 Pump mixture to dump in preparation for throughput test. (We filled the LN2 cold trap bath during the blowout.)
1134 IVC leak = 245 pbarL/s, Main bath = 299 mbar above 1 atm, falling quickly
1137 IVC leak = 247 pbarL/s, Main bath = 212 mbar above 1 atm
1140 IVC leak = 255 pbarL/s, Main bath = 170 mbar above 1 atm
1145 IVC leak = 269 pbarL/s, Main bath = 167 mbar above 1 atm. Stop pressurizing main bath.
1225 Start pumping out main bath with scroll pump
1235 Main bath < 1 mbar, looks like all the LN2 is out. IVC leak = 170 pbarL/s.
1255 Pressurize main bath with He to 265 mbar above 1atm. No increase in IVC leak signal.
Throughput test procedure, Cold Trap 2:
  1. All mixture in dump, LN2 traps cold, condenser & still valves open (3He pump on - optional)
  2. Open V9, V13b, V12b+speedivalve, V3. Wait for G1 to be close to G2.
  3. Close V12b+speedivalve and V3, open V1
  4. monitor G1
1300 Perform mixture throughput test at MC = 77 K using above procedure. Let G1 rise to 560 mbar before Step 3, then it falls to 31 mbar, then rises but very slowly. Throughput 0.34 mbar/min. Compare with 48.0 mbar on three days ago.
1310 Pump mixture back to dump
1320 Perform a second mixture throughput test. Let G1 rise to 568 mbar before Step 3, then it falls to 32 mbar, then rises but very slowly. Throughput 0.27 mbar/min.
Begin warming up.
1340 Let about 0.04 bar He gas into IVC. MC temperature rising 0.1 K/min
1410 MC(Cernox) = 80.1 K, Sorb = 140.7 K, both rising
1425 Let N2 into the IVC up to about 0.2 bar
1440 MC(Cernox) = 80.7 K, Sorb = 143.3 K, main bath outer surface = 22.9 C
1440 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.
1450 MC(Cernox) = 80.9 K, Sorb = 145.3 K, main bath outer surface = 22.0 C
1500 MC(Cernox) = 81.3 K, Sorb = 149.8 K, main bath outer surface = 21.4 C
1540 MC(Cernox) = 86.3 K, Sorb = 177.2 K, main bath outer surface = 20.2 C
1550 MC(Cernox) = 87.9 K, Sorb = 183.2 K, main bath outer surface = 20.0 C
1605 MC(Cernox) = 90.8 K, Sorb = 192.2 K, main bath outer surface = 19.7 C
1615 MC(Cernox) = 92.8 K, Sorb = 198.2 K, main bath outer surface = 19.5 C
1625 MC(Cernox) = 94.9 K, Sorb = 203.7 K, main bath outer surface = 19.4 C
1630 Main bath pressure hit 1 over 1atm (about 7 PSI). Release this to recovery. Got a few cubic feet on the meter.
1635 MC(Cernox) = 96.9 K, Sorb = 208.8 K, main bath outer surface = 19.4 C
warming time constant is around 16.5 hours, should hit 273 K Sunday @ 4:30 am.
1650 Perform a third mixture throughput test, now at MC = 100 K. Let G1 rise to 571 mbar before Step 3, then it falls to 34 mbar, then rises but very slowly. Throughput 0.10 mbar/min.
1655 When MC hit around 100 K I noticed that the resistance of the short to chassis had started to rise, from 250 Ω to 350 Ω. Now, with the tower around 102 K, the resistance is much higher, around 1 MΩ.
1700 Now the short is around 80 kΩ.
1705 Short is around 100 kΩ, not very stable.
1710 MC(Cernox) = 104.1 K, Sorb = 224.6 K, main bath outer surface = 19.4 C
1710 Short has jumped up to 780 kΩ.
1715 Pump mixture out of fridge and LN2 cold trap to dump
1715 Short is reading 1.1 MΩ.
1720 MC(Cernox) = 106.1 K, Sorb = 229.1 K, main bath outer surface = 19.5 C
1720 Short is reading 1.1 MΩ.
2235 MC(Cernox) = 161.5 K

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