2019/10/30 (Wednesday)
| Status: Mixture cryocleaned 6 times. LN2 transfer yesterday, throughput steadily getting worse toward end. Beginning 2nd attempt at Run 71 cooldown. | |
| 0925 | MC(Cernox) = 79.1 K, Sorb = 157.8 K, IVC = 1.6 mbar, G2/G1 = 528/593 mbar, Level resistor = 0.983 kΩ |
| 0925 | Turn on 3He pump and open V6 to 12.8%, reestablishing circulation like yesterday. P1 (still) quickly falls below 1 mbar. This already suggests a blockage. |
| 0930 | Close V12b speedivalve to assess throughput. G1 falls at 51 mbar/min. We still have throughput! |
| Throughput test procedure, Cold Trap 2: |
- All mixture in dump, LN2 trap 2 cold, condenser & still valves open (3He pump on - optional)
- Open V9, V13b, V12b+speedivalve, V3. Wait for G1 to be close to G2.
- Close V12a+speedivalve and V3, open V1
- monitor G1
| 0940 | Perform mixture throughput test at MC = 77 K using above procedure with 3He pump on. Let G1 rise to 560 mbar before Step 3, then it falls to 60 mbar, then rises. Throughput = 53.3 mbar/min. [image not archived: cool.svg] A little higher than last time, 2019 Sep 21 |
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| 0945 | Pump out IVC with scroll pump, then with turbo pump. |
| 1000 | Start Pfeiffer Leak Detector using scroll pump as the forepump. |
| 1005 | Electrical check on all DIBs. LED2 on DIB1 open. FET TSense DIB3 open. DIB2 qI seems to be shorted on the FET Gate line to chassis, 10 MOhm. |
| 1020 | LD signal on IVC = 203/1400 pbarL/s with Turbo pump valved in/out |
| 1030 | LD signal on IVC = 184/1300 pbarL/s with Turbo pump valved in/out |
| 1035 | As mentioned on 10/25 DIB2pC currently has no SQUID feedback resistor. Modify a Dsub50 diverter board to add a 1 kOhm resistor on the PC feedback line. Hopefully this won't add too much noise, since we think the phonon noise is dominated by the shunt resistance on the input side of the SQUID amp. |
| 1040 | LD signal on IVC = 179/1480 pbarL/s with Turbo pump valved in/out |
| let leak detector stabilize while pumping on IVC, turbo valved out | |
| 1045 | LD signal on IVC = 1660 pbarL/s |
| 1045 | Begin blowing out LN2. Main bath (G3) = 670 mbar above 1atm. |
| 1050 | LD signal on IVC = 1630 pbarL/s |
| 1055 | LD signal on IVC = 4000 pbarL/s and climbing. Main bath pressure falling, blowout probably almost finished. |
| 1100 | LD signal on IVC = 11000 pbarL/s and climbing. Main bath (G3) = 228 mbar above 1atm and flat. Looks like a leak from MB to IVC. |
| 1100 | Stop pressurizing main bath. Turn off leak detector. |
| 1105 | Start pumping out main bath with scroll pump. Takes 12 minutes to fall to 1 mbar. |
| 1120 | Leaving main bath evacuated, move scroll pump to leak detector and start LD again. |
| 1120 | Main bath has crept up to 4 mbar. Start pumping main bath with 4He pump to keep the pressure low. |
| leak checks with main bath =0.28 mbar: | |
| 1135 | LD signal on IVC = 159/1100 pbarL/s with Turbo pump valved in/out |
| 1135 | Try squirting around stripline tube at top. No change. Let a little He into main bath, the amount between v2a and v5a. Main bath rises to 2.8 mbar. No noticeable change in leak signal. |
| 1140 | Let enough He into main bath to get pressure up to 13 mbar. No noticeable increase in leak signal. IVC = 1500 pbarL/s. |
| 1140 | Let about 4/30 bar of He into IVC. Now leak signal rises noticeably, → 7000 pbarL/s and rising. |
| 1150 | Pump out IVC in steps with 4He pump. At around 2/30 bar LD signal starts to fall. |
| 1155 | Pump Main Bath down to 5 mbar, LD → 3100 pbarL/s and falling. |
| 1200 | Main Bath = 0.3 mbar, LD → 1170 pbarL/s and flattening. Stop pumping MB. |
| 1205 | Try letting some N2 into Main Bath. Probably it isn't cold enough to condense but it will probably take a lot to get it to 1 atm. |
| 1215 | Change N2 cylinder and let more N2 into MB. P2 doesn't go up past 100 mbar but the mechanical valve is going up. |
| 1225 | Pressurize MB with N2 up to G2 = 535 mbar+1atm. Note P2 still reads only 170 mbar. |
| 1235 | Leak signal on IVC = 942 pbarL/s. Now we can try squirting He down into the MB. |
| 1240 | Try squirting about 2-meter hose length of He into MB from top, first at the empty port (top of fridge), then down the transfer tube raised about 1 inch (above funnel), then down the transfer tube fully inserted (bottom of MB). No noticeable increase in signal, this doesn't seem to be enough helium to be noticeable. |
| 1245 | Try again with full hose-lengths of He, maybe 6-7 meters. When squirting to bottom of MB, signal rose 920→1650 pbarL/s, after a bit of a delay. |
| but the above was not repeatable, I think I accidentally squirted in more than I thought… | |
| 1255 | Try again with 1-second squirts of He. No change at first two positions. When squirting to bottom of MB, signal rose 1820→1970 pbarL/s slowly, over a few minutes. |
| 1330 | Try again with 1-second squirts of He. Wait a minute or so after each squirt. No change at first position. At second position (1 inch above funnel) signal rose from 1830→1850 pbarL/s over 45 sec. At third position (bottom of MB) signal rose to 1920 pbarL/s. |
| 1350 | Try again with 3-second squirts of He. Wait a minute or so after each squirt. Start at 1950 pbarL/s. No change at first or 2nd position. When squirting to bottom of MB, signal rose 1950→2340 pbarL/s after 2 min. Settles around 2480 pbarL/s. |
| 1400 | MC(Cernox)/Sorb = 80.4/176.2 K |
| 1410 | Let about 0.31 atm N2 into IVC. MC and Sorb temperatures rise noticeably. |
| 1415 | MC(Cernox)/Sorb = 86/201 K |
| 1425 | Cryostat vacuum jacket = 1.2 mbar |
| 1425 | MC(Cernox)/Sorb = 94/220 K |
| 1430 | Let 25 mbar N2 gas into vacuum manifold. Then open cryostat vacuum jacket valve to let this into the vacuum jacket. Vacuum jacket → 2.2 mbar Let 25 mbar N2 gas into vacuum manifold. Then open cryostat vacuum jacket valve to let this into the vacuum jacket. Vacuum jacket → 2.5 mbar Let 25 mbar N2 gas into vacuum manifold. Then open cryostat vacuum jacket valve to let this into the vacuum jacket. Vacuum jacket → 3.0 mbar Let 30 mbar N2 gas into vacuum manifold. Then open cryostat vacuum jacket valve to let this into the vacuum jacket. Vacuum jacket → 4.0 mbar |
| 1435 | Let 30 mbar N2 gas into vacuum manifold. Then open cryostat vacuum jacket valve to let this into the vacuum jacket. Vacuum jacket → 4.6 mbar Let 30 mbar N2 gas into vacuum manifold. Then open cryostat vacuum jacket valve to let this into the vacuum jacket. Vacuum jacket → 5.4 mbar |
| 1440 | MC(Cernox)/Sorb = 99.2/231.5 K |
| 1510 | MC(Cernox)/Sorb = 108.5/248.7 K these imply a MC warming time constant (room temp = 296 K) of 10.3 hours, which suggests MC will reach dew point (281 K) tomorrow around 17:15 |
| 1540 | MC(Cernox) = 115.9 K now the time constant looks longer, 12.4 hours, which suggests MC will reach dew point tomorrow around 22:30 |
| 1550 | Turn on MC and Still heaters to 20 mW each |
| 1610 | MC(Cernox) = 122.45 K now the time constant looks even longer, 13.5 hours, which suggests MC will reach dew point tomorrow Friday 1:10 am. |
| 1635 | IVC = 0.48 atm. Adjust this by pumping out a little with scroll pump, IVC → 0.43 atm. Currently MC = 127.7 K, so this should end up close to 1 atm at room temperature. |
| 1635 | Pump mixture out of fridge to dump |
| 1640 | Noticed an uptick in MC temperature when I let in some fresh (warm) N2 into IVC. Let's play with this - let in N2 up to near 1 atm, then pump out again. |
| 1645 | Let N2 into IVC → 0.86 atm, see increase in warming rate. Now pump it back down. |
| 1705 | Pumped IVC → 0.45 atm. MC = 134.3 K, so this will be pretty close to 1 atm when it reaches room temperature. Pumping it out seened to reduce the cooling rate - why does this have a cooling effect? Maybe we preferentially pump out the warmer part of the gas. So not sure there was any net gain to the warming. |
| 1710 | Pump mixture out of LN2 Trap 2 to dump. |