2021/04/29 (Thursday)
- Lab in-person: Matt
- Virtual partner: Zach
| Status | Run 74 in progress. Recooled after redoing IVC indium seal to fix IVC leak. But it didn't work - leak reappeared during LHe transfer yesterday. |
|---|---|
| 0925 | MC(Cernox)/Sorb/1K Pot = 4.26/5.9/4.72 K, IVC = 220 μbar, G1(fridge) = 550.5 mbar. |
| 0940 | Recovery = 430657 cuft / 15.9 cuft/hr |
| 1240 | Matt enters lab |
| 1240 | MB = 15.3% |
| 1240 | MC(Cernox)/Sorb/1K Pot = 4.27/5.9/4.77 K, IVC = 220 μbar, G1(fridge) = 550.5 mbar. |
| 1240 | Start pumping on IVC with Scroll Pump. |
| 1250 | Scroll on IVC = 0.14 mbar |
| 1250 | Carefully open Turbo pump valve and start pumping IVC with Turbo and Scroll in parallel |
| 1255 | Turbo+Scroll on IVC = 25 μbar |
| 1255 | Valve out Scroll pump, pump IVC with Turbo only |
| 1300 | Turbo on IVC = 16 μbar |
| Looking back at the last successful cooldown, Feb 17, note that there was concern at that time that the IVC pressure was higher than normal at the end of the LHe transfer. This leak may have been slowly developing. But we were able to cool to base at that time. I wonder if we can get the IVC pressure low enough to try the 1K Pot | |
| 1305 | Turbo on IVC = 12 μbar. With Turbo valved out for 1 minute, IVC = 74 μbar. So it has gone down. But this is likely too high for the 1K Pot to work - this pressure is as high as the initial exchange gas, and that's at 77K. So there's a lot of helium in there. |
| 1325 | Turbo on IVC = 6.3 μbar. With Turbo valved out for 1 minute, IVC = 40 μbar. so it is still going down. Is there any chance we can get it low enough to start the 1K Pot? The leak seems not as bad now, since we are able to pump it lower with the scroll. Is that because the bath is lower? The leak showed up when the bath was above like 15%. |
| 1350 | Turbo on IVC = 2.5 μbar. With Turbo valved out for 1 minute, IVC = 30 μbar. |
| the likelihood that we could actually limp by in the current conditions, get enough gas out of the IVC to run the pot and cool down, seems low. As far as we can tell the heavy leak recurs when the bath level rises above a certain level. | |
| it may be interesting to test that hypothesis by doing another transfer now. But haven't we tested it twice already? Not sure what more we'd learn. Likely the pressure changes would be confusing and hard to interpret in any detail. | |
| 1415 | Turbo on IVC = 1.4 μbar. With Turbo valved out for 1 minute, IVC = 22 μbar. |
| 1420 | Stop pumping IVC. |
| 1420 | Recovery = 430732 cuft / 16.0 cuft/hr |
| 1425 | IVC = 22 μbar |
| for the fun of it, before letting He into the CVJ, let's lower the transfer stick into the MB in order cause a boiloff, see if the IVC pressure changes. | |
| 1425 | Insert transfer stick into MB. Recovery rate increases but IVC pressure doesn't change. |
| 1430 | IVC = 16 μbar. So it actually went down. That's interesting - it could be that the upper parts of the IVC were rather warm, and the cold gas escaping out the top now has cooled it a bit. |
| 1435 | IVC = 24 μbar |
| 1435 | Isolate IVC and switch pumping line over to Cryostat Vacuum Jacket |
| 1440 | MB = 12.5% |
| 1445 | Let 2.2 mbar He gas into vacuum manifold. Then open cryostat vacuum jacket valve to let this into the vacuum jacket. Vacuum Jacket → 0.054 mbar. |
| recovery rate, MB pressure, MC temperature all increase | |
| 1450 | Recovery = 190 cuft/hr. MC = 4.35 K. MB = 11.2% / 244 mbar+1atm (was 158 mbar+1atm before) |
| 1455 | Recovery = 195 cuft/hr. MC = 4.36 K. MB = 9.5% / 252 mbar+1atm |
| 1500 | Recovery = 188 cuft/hr. MC = 4.36 K. MB = 8.1% / 233 mbar+1atm. CVJ has dropped to 0.012 mbar. |
| 1505 | Recovery = 169 cuft/hr. MC = 4.36 K. MB = 6.4% / 218 mbar+1atm. |
| 1510 | Recovery = 156 cuft/hr. MC = 4.36 K. MB = 5.6% / 211 mbar+1atm. |
| 1445 | Let 3.4 mbar He gas into vacuum manifold. Then open cryostat vacuum jacket valve to let this into the vacuum jacket. Vacuum Jacket → 0.063 mbar. |
| MC temperature and MB pressure rise again | |
| 1520 | Recovery = 285 cuft/hr. MC = 4.43 K. MB = 2.9% / 301 mbar+1atm. |
| 1525 | Recovery = 296 cuft/hr. MC = 4.45 K. MB = 0.9% / 293 mbar+1atm. |
| 1530 | Recovery = 280 cuft/hr. MC = 4.47 K. MB = -1.0% / 275 mbar+1atm. |
| 1535 | Recovery = 267 cuft/hr. MC = 4.54 K. MB = 268 mbar+1atm. |
| 1540 | Let 3.4 mbar He gas into vacuum manifold. Then open cryostat vacuum jacket valve to let this into the vacuum jacket. Vacuum Jacket → 0.054 mbar. |
| 1540 | Start pumping mixture to dump. MC temperature dips to 4.45 K but then starts rising again. |
| 1545 | Recovery = 371 cuft/hr. MC = 4.82 K. MB = 327 mbar+1atm. |
| 1550 | CVJ = 0.034 mbar |
| 1555 | Recovery = 345 cuft/hr. MC = 5.40 K. MB = 291 mbar+1atm. |
| 1600 | Isolate CVJ, switch pumping line over to IVC port |
| 1600 | Recovery = 308 cuft/hr. MC = 5.88 K. MB = 280 mbar+1atm. |
| 1605 | IVC = 22 μbar. Start pumping IVC with Turbo, we'll see how low it goes now. |
| 1610 | Recovery = 241 cuft/hr. MC = 7.86 K. MB = 251 mbar+1atm. |
| 1615 | Stop pumping mixture to dump. Dump = 735.6 mbar. Looks like it would hit 737 or 738 mbar if we left the pump on for a while. Turn off 3He pump, close IGH valves. |
| 1620 | Turbo on IVC = 3.0 μbar. With Turbo valved out for 1 minute, IVC = 25 μbar. So I guess leak is about as bad as before. Or it's just a slow process to get out the helium. |
| 1620 | Recovery = 178 cuft/hr. MC = 9.77 K. MB = 216 mbar+1atm. |
| 1625 | MC/1K Pot/Sorb = 10.6/>7/21.1 K |
| 1625 | Recovery = 431151 cuft (431150.9 @ 16:25:09) |
| 1640 | Turbo on IVC = 5.4 μbar. With Turbo valved out for 1 minute, IVC = 34 μbar. Going up with temperature presumably |
| 1640 | Valve out Turbo, we'll leave IVC isolated and watch the pressure. |
| 1640 | Recovery = 85 cuft/hr. |
| 1650 | Matt exits lab |
| 1720 | Recovery = 16 cuft/hr. MC(Cernox) = 35 K |
| 1725 | IVC = 140 μbar |
| 1821 | Recovery = 431196 cuft / 2.9 cuft/hr. MC(Cernox) = 45 K |
| 1915 | Recovery = 0.15 cuft/hr. MC(Cernox) = 51 K |
| After this recovery has completely stops, at least until the next morning, that's a little unusual. | |
| 2025 | IVC = 40 mbar. MC(Cernox)/Sorb = 59/116 K |
| 2045 | IVC = 54 mbar. MC(Cernox)/Sorb = 61/125 K |
| 2205 | IVC = 140 mbar. MC(Cernox)/Sorb = 76/158 K |