2018/05/16 (Wednesday)
| Status: Initial LHe transfer yesterday | |
| 0905 | MC(Cernox)/Sorb/1K Pot = 4.9/8.7/6.7 K, G1(fridge) = 545 mbar, MB = 51.6% |
| 0905 | Turbo on IVC = 1.4 nbar |
| 0910 | Fill LN2 cold trap bath |
| 0915 | Check pressure in 1K Pot: 2.5/30 bar on mechanical gauge. Pump out with scroll pump. Falls from 6.7→6.53 K, 0.4 mbar |
| 0925 | Switch to pumping 1K Pot with 4He pump. When we closed off the pump to do the switch, the pot pressure rose back up off-scale on p2 to something like 2.5/30 bar again. open 4He pump exhaust to recovery and open red recovery valve |
| 0925 | 1K Pot = 6.55 K / 0.28 mbar |
| 0927 | Open needle valve several degrees. No change in pot pressure; temperature actually goes up at first to 6.7 K, then after half a minute starts to fall very quickly, must have got some LHe in there |
| 0930 | 1K Pot = 4.74 K / 0.30 mbar, temperature still falling |
| 0935 | 1K Pot = 4.78 K / 0.32 mbar |
| 0950 | Have tried opening the needle valve. Pressure does not increase. Temperature continues to rise. Open the needle valve completely, many rotations. The temperature is well above 4K, has risen back to 6.5 K = why?? Like no LHe is going in. But earlier we got it to fall to 4.7 K, as if some LHe was going in. |
| 1100 | Leaving the 1K Pot alone for a while, it went through some oscillations. The 4He pump is pumping on it and the needle valve is closed. Temperature fell from 6.6 K to 5.3 K then rose to 6.2 then fell to 5.8 etc, like a damped oscillator. |
| 1105 | With needle valve completely closed, close off pump and see how fast pressure rises: |
| minutes | mbar (P2) |
|---|---|
| 0 | 0.3 |
| 0.5 | 6 |
| 1.0 | 27 |
| 1.5 | 120 |
| 1.8 | 1000 (off-scale) |
| 1130 | Discussing with Paul Crowell, he says the symptoms strongly suggest that it's plugged. One piece of evidence is that when we close off the pump and open the needle valve wide, the pressure only goes up a few inHg, instead of rising to 1 atm. Another symptom is that pressure doesn't really increase when you are pumping even if you have the needle valve wide open. |
|---|---|
| Paul suggests removing the needle valve shaft completely. If it is opened enough turns the shaft becomes loose and can be pulled straight up. There are o-rings at the top on the shaft that seal the shaft from atmosphere - these may be worn out and need replacement. He also said that there is an extender on the fill tube that can be unscrewed, if we want to look at that. Of course we need to warm up to do that. | |
| 1155 | Try another test to see how fast the 1K Pot pressure rises when the pump is closed off, but this time with needle valve open 5 full rotations: |
| minutes | mbar (P2) |
|---|---|
| 0 | 0.28 |
| 0.5 | 6.5 |
| 1.0 | 36 |
| 1.5 | 1000 (off-scale) |
| so it goes up a little faster with needle valve wide open. Only goes up to 2/30 bar on mechanical gauge. | |
| 1205 | Close 1K Pot needle valve and speedivalve. Close off valve to 4He pump and turn off pump. Close recovery valve. |
| 1205 | Stop pumping IVC with turbo. IVC pressure = 14 nbar |
| 1215 | Let 2 hose-lengths He into IVC. IVC → 100 ubar. MC and 1K Pot temperatures fall to ~4.5 K |
| 1230 | MB = 47.0%. Recovery rate = 178 sec/sqft |
| 1235 | Let 1.9 mbar He gas into vacuum manifold. Then open cryostat vacuum jacket valve to let this into the vacuum jacket. Vacuum jacket → 46 μbar Recovery rate → 30 sec/sqft |
| 1240 | MB = 45.4%. Recovery rate = 15.5 sec/sqft |
| 1250 | MB = 42.1%. Recovery rate = 16.0 sec/sqft |
| 1330 | MB = 33.8%. Recovery rate = 31 sec/sqft |
| 1330 | Cryostat vacuum jacket = 7.4 μbar (it's drifted down) |
| 1335 | Let 1.9 mbar He gas into vacuum manifold. Then open cryostat vacuum jacket valve to let this into the vacuum jacket. Vacuum jacket → 34 μbar |
| 1340 | MB = 32.3%. Recovery rate = 21 sec/sqft |
| 1410 | MB = 22.9%. Recovery rate = 18 sec/sqft |
| 1435 | MB = 16.4%. Recovery rate = 21 sec/sqft |
| 1455 | MB = 11.7%. Recovery rate = 21 sec/sqft |
| 1520 | MB = 6.4%. Recovery rate = 20.5 sec/sqft |
| 1540 | Pump mixture to dump |
| 1600 | MB = -1.0%. Recovery rate = 28 sec/sqft |
| 1600 | Cryostat vacuum jacket = 14 μbar |
| 1600 | Let 2.2 mbar He gas into vacuum manifold. Then open cryostat vacuum jacket valve to let this into the vacuum jacket. Vacuum jacket → 40 μbar |
| 1605 | MC(Cernox)/1K Pot/Sorb = 4.4/5.2/6.6 K. Pot and Sorb rising steadily. |
| 1750 | MC(Cernox) = 13 K |
| 1920 | MC(Cernox) = 42.2 K |
| 1950 | MC(Cernox) = 47.44 K |