2020/03/11 (Wednesday)
| Setup | Run 72. DIB 1/3/4 → Stripline 43/41/48 → Cable 3/2/1 → nothing/nothing/accessory_interposer → HV_Conn 1/3/2 → HV 1/2 → DCRCX(4)/DCRC55(1). DCRCs off overnight. Lead/poly shield erected (4 lead walls, 2 poly walls). |
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| Status | Warming up. All mixture in dump. 1K Pot was pumped out at 7K, now isolated. LN2 Trap 1 is warm, should be checked. Small amount of He in IVC and in cryostat vacuum jacket. |
| 0200 | He recovery meter = 341340 cuft, rate = 1.5 cuft/hour |
| 0844 | He recovery meter = 341342 cuft, rate = 0.3 cuft/hour |
| 0930 | MC(Cernox)/Sorb = 110/203 K and rising |
| 0955 | Check pressure in 1K Pot by opening 1K Pot speedivalve : about 60 mbar according to mechanical gauge. Presumably this was frozen air; either that or helium leaked in through the needle valve overnight. Pump out with 4He pump. |
| 1000 | Check pressure in cryostat vacuum jacket: 54 ubar. |
| 1005 | Let 4.0 mbar N2 gas into vacuum manifold. Then open cryostat vacuum jacket valve to let this into the vacuum jacket. Vacuum Jacket → 0.220 mbar. |
| 1030 | After pumping out 1K Pot, leaving it open to P2 shows the pressure rises to above 12 mbar over 10 minutes. Leaving the 1K Pot isolated for 20 minutes then checking the pressure again, it's off-scale on P2, about 30 mbar according to mechanical gauge. So it looks more like leakage from the bath to the pot, no real evidence that we got air out of the pot. |
| 1035 | Try closing the 1K Pot needle valve a little tighter (it had a little give left). Pump out 1K Pot again with 4He pump. Then stop pumping and leave it open to P2. It still goes up pretty fast, 18 mbar after 10 minutes. |
| 1045 | Open 1K Pot needle valve a few turns, letting gas from the MB into the pot. Pressure goes up quickly. |
| 1050 | Close 1K Pot speedivalve. Remove needle valve completely, and put a plug into the shaft. O-rings look fine. Needle valve is frosty, not surprisingly. We'll want to make sure there's no frost in the pot before flushing it again, so we may not be able to proceed immediately. |
| 1100 | He recovery meter = 341342.34 cuft, rate = 0.3 cuft/hour. Close recovery valve from MB. |
| 1115 | Put a little vacuum grease on needle valve o-rings and put it back in the shaft, so the o-rings are sealing the shaft. But leave the needle valve completely open. |
| 1120 | Begin pumping out the Main Bath and also the 1K Pot (V1a and 1K Pot Speedivalve both open) with the scroll pump. Falls below 1 mbar in 10 minutes. |
| 1140 | Pressurize MB and 1K Pot to 1atm+305 mbar on G3. |
| 1145 | Begin pumping out MB and 1K Pot again. |
| 1205 | MB+Pot pressure down to 0.34 mbar, flat. Now close 1K Pot needle valve and V1a, so we are only pumping on 1K Pot through speedivalve. Pot pressure falls a lot, to 0.014 mbar. Close scroll pump valve to watch 1K Pot pressure rise. Creeps up to 0.026 mbar after a couple of minutes. |
| 1210 | Pressurize 1K Pot to over 1 atm. When G3 reaches about 600, heard a leak somewhere - then pressure fell to about 350. Maybe a relief valve? |
| 1210 | Pump out 1K Pot again with scroll pump. Falls to 0.014 mbar again quickly. |
| 1215 | Pressurize 1K Pot again - around 450 mbar+1atm another release heard, pressure fell again to 350 mbar. Pump out again with scroll pump. |
| 1220 | Pressurize 1K Pot again - I found the relief valve, at the 1K Pot port at the top of the fridge, on the fridge side of the speedivalve. Pump out again with scroll pump. |
| 1225 | Pressurize MB with He to about 100 mbar+1atm. Check pressure in 1K Pot: 2.0 mbar and rising. As before it's clear that the needle valve leaks by a couple mbar/minute. |
| 1230 | Pump 1K Pot out again, this time with He in the MB. Doesn't pump down quite as low, bottoming out at 0.028 mbar instead of 0.014. |
| 1235 | Pressurize 1K Pot again with helium, 350 mbar+1atm. Pressure falls by around 1.5 mbar/minute, leaking out of the needle valve at about the same rate that it leaked in. |
| 1240 | Open 1K Pot needle valve all the way (around 16 full turns). 1K Pot pressure falls quickly to 115 mbar+1atm as it equalizes with the MB. |
| 1315 | Check pressure in IVC: 3.4 mbar. Probably some of that is air that accumulated during the run. Pump out with scroll pump, then turbo pump. |
| 1350 | Fill IVC with about 0.68 bar He. MC = 133 K. So maybe 0.68 bar is a little high, if it warms to room temperature it could rise to 1.5 bar (though probably less since the Ebox is always room temperature). Should maybe pump some out before the end of the day. For now though it's making the fridge warm faster. |
| 1350 | MC(Cernox)/Sorb = 133/250 K. Sorb thermometer is at maximum. |
| 1355 | Check warm LN2 Cold Trap 1: 17.0 mbar. Pump out with scroll pump. |
| 1410 | Check LHe Cold Trap (open V1, Condenser speedivalve closed, read at G1): 4.3 mbar. Pump out with scroll pump. |
| 1420 | Condenser/Still = 0.2/0.03 mbar. Pump out with scroll pump. |
| 1435 | Put LN2 Trap 1 in Dewar and fill bath |
| 1435 | Start pumping out MB and 1K Pot with scroll pump. V1a and both 1K Pot valves all fully open. |
| 1450 | Pressurize MB and 1K Pot with helium to 207 mbar+1atm. |
The plan is to transfer LN2 tomorrow. We want to thoroughly flush the 1K Pot. How should we leave things tonight?
- Cryostat vacuum jacket: if we leave gas in it we will be warmer tomorrow - otherwise we may not get above freezing, and any water ice will still be present. But then we'd need to pump it out tomorrow. How long does it take? Maybe a few hours is OK, could do that in the morning. Need scroll pump briefly, then leave turbo on it.
- IVC: currently the pressure is too high to leave it, should pump it down to safe level so no chance of overpressure as it warms overnight. It is probably sufficiently pumped out so tomorrow could just lower it to exchange gas level… or alternatively pump it out first then add exchange. Can't do this simultaneously with pumping out jacket, would need to be before or after.
- Mixture: we could do cleanings today and/or tomorrow but maybe not necessary, since running the fridge should clean it pretty thoroughly. Maybe do one or more cleanings anyway.
- 1K Pot: we've flushed it a few times today but it's below freezing, so any water ice may still be present. Could flush it more tomorrow - in fact we generally flush on the day of the LN2 transfer. Overnight should leave it full of helium. Not sure whether to close the needle valve, probably leave it open to prevent overpressure. Make sure MB seals are tight as possible. |
| 1525 | Start cryocleaning mixture through LN2 Cold Trap 1, V6 = 12.8% |
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| 1535 | Increase V6→13.1% to restart flow |
| 1550 | Pump IVC down to about 0.48 bar according to mechanical gauge. MC(Cernox) = 146 K. This should keep it under 1 atm as it warms to room temperature. |
| 1550 | Increase V6→13.2% to restart flow |
| 1600 | Increase V6→13.3% to speed up flow |
| 1625 | Stop cleaning through Trap 1 after 60 min. G2 flow pressure was 560-805 mbar. Pump mixture to dump. Removed 13.4 mbar. |
| 1650 | MC(Cernox) = 151 K. IVC = 0.52 bar. |
| 1700 | Cryostat vacuum jacket = 0.14 mbar. Down a bit from earlier for some reason. |
| 1700 | MB = 267 mbar+1atm, increasing as the cryostat gets warmer. Let some pressure out from the top of the MB. MB → 113 mbar+1atm. |