2019/04/18 (Wednesday)
| Status | Room temperature. All mixture in dump. LN2 traps warm. 1K Pot needle valve closed. 1 atm nitrogen exchange gas in IVC. Cryostat vacuum jacket pumped out. The LN2 traps and the 4He trap and fridge still need to be checked for contaminant pressure and pumped out. |
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| 0930 | Finish 4He Pump rebuild. |
| 1110 | Fill 4He pump with Leybonol LVO 100 oil |
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| 1130 | Cap off 4He Pump inlet, leave exhaust port open. Turn on pump - sounds OK. A little oil vapor can be seen drifting out of exhaust port. Try opening gas ballast - pump gets louder and significantly more vapor comes out of exhaust. |
| 1135 | Oil level is lower after running for a few minutes, so put in some more |
| 1140 | Run 4He pump for a few minutes. Oil level remains OK, about 40%. |
| 1155 | Check pressure at P2, the 1K Pot pumping line. 4.5 mbar. Connect line to 4He pump, turn on pump, then open valve at pump. P2 quickly falls to 0.02 mbar. After a couple of minutes falls to 0.017 mbar. Looks like the pump works. |
| 1215 | Oil level is about 40% with pump off, 30% with pump running at low input pressure. |
| 1255 | Finish dismantling lead stack. |
| Let's check the pressures in the cold traps, using the 4He pump to put it through its paces. | |
| 1300 | Pump out lines to G1, then check LN2 Trap 1 pressure: 112.5 mbar. Let this open to pump line: P2→ 50 mbar, so we'll see how the pump does with this. Open valve to pump - pump sound changes briefly but remains smooth. Continue pumping out LN2 Trap 1. |
| 1310 | Check LN2 Trap 2 pressure: 2.9 mbar. Pump out with 4He pump. |
| 1320 | Check LHe Trap pressure: 82.7 mbar on G1. Check this by opening V1 with condenser valve closed. Open this to pump line: P2→ >1000 mbar. Huh. Try pumping out with 4He pump - pump does not seem to strain much at all, pumps down quickly. |
Interesting observation:
| pressure at G1 before opening pump line | pressure at G1 after opening pump line | pressure at P1 after opening pump line | |
|---|---|---|---|
| LN2 Trap 1 | 114.2 | 46 | 50 |
| LHe Trap | 84.2 | 15.7 | >1000 |
If the P1 gauge (Pirani) is tuned to air, then it would make sense that the LN2 Trap1 pressure reads correctly on it, since it was probably filled with air. But the contents of the LHe Trap must be different because clearly P1 read wrong. Was it full of hydrogen? This site suggests hydrogen should cause the gauge to read too low not too high; some hydrocarbons like methane and butane would make it read high. But both of those have boiling points higher than 77K so you'd expect the LN2 traps to get them. (The only gases I can find with boiling points between 4K and 77K are hydrogen and neon.)
| 1400 | Check pressure on condenser side of fridge: 2.4 mbar. Check pressure on still side of fridge (at P1): 1.5 mbar. Pump out with 4He pump. |
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| 1420 | Pumped the Still (P1) down to 0.55 mbar. Stop pumping and turn off 4He pump. (Pump was pretty warm, not sure whether it ran warmer before the rebuild). |
| 1505 | Drop main bath. |
| 1510 | Erect clean tent. |
| 1530 | Begin tower deinstallation. |
 | For the next run we will build a diverter board so the bias lines bypass the SQUET at the end of the stripline. We have boards with extensions out to one side for wire connections - here we see the way we'd want to orient this board so there's room for it, so the extension sticks out to the right, opposite the stripline on the left side. |
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| Probably the easiest position for the diverter is NW, which is where we currently run the HV (DIB4pA QET&return). So we could use those same connections. This is Tower Face 1, and the next face to the left is Tower Face 2. So we will use Pins 1&2 on Tower Face 2. |
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| 1600 | IVC is open. SQUETs are removed. |
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