2018/07/25 (Wednesday)
| status: circulation and 1K Pot suspended, mixture in fridge, IVC closed off. MC/Still heaters on. Investigating helium in IVC | |
| overnight: Tower temperature settling downward, from 9.4 to 8.5 K. Sorb flat. | |
| the cooling of the Tower over time indicates increasing thermal contact with the main bath. This could be a steadily increasing amount of helium in the IVC but more likely it is a reverse effect from the warming of the gas above the bath as the LHe boils down - the walls of the IVC get warmer which increases the conductivity of the helium inside. | |
| 0815 | Tower/Sorb/1K Pot = 8.52/9.6/>7 K, MC/Still = 20/20 mW, IVC = 40 nbar. MB = 31.5% |
| 0815 | Turn off MC/Still heaters. Tower and Sorb fall temperatures fall. IVC → 34 nbar. |
| this morning: look at how quickly Tower settles to 4.4K with the heaters off (and see if IVC pressure changes). Then turn them back on to 20/20 mW and see how fast till it rises and if it hits the same level as before. Then start pumping on the IVC again and see how hot it gets and how quickly. When it hits say 12 K or something try closing the turbo valve again and see if this slows down the warming. Note IVC pressure at all points. | |
| 0930 | Tower = 6.3 K, IVC = 30 nbar |
| 0935 | Fill LN2 cold trap full. |
| 1050 | Tower = 6.0 K, IVC = 30 nbar Tower is settling to something like ~5.75 K with a time constant of ~41 min |
| 1053 | Turn on MC/Still heaters = 20/20 mW |
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| 1140 | Tower warmed to 8.4 K with a time constant of ~4.5 min |
| 1153 | Tower = 8.3 K, IVC = 40 nbar |
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| 1154 | Open turbo pump valve. Tower rises pretty much linearly at ~68 mK/min |
| 1250 | Tower = 12.0 K, IVC = 2.5 nbar (pumping) Close turbo pump valve. |
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| As seen above, when Turbo pump was closed (at 12 K) the rise in temperature starts to slow, though it's a pretty smooth transition. | |
| 1420 | Tower peaks at 14.2 K then starts falling. Sorb followed the same pattern, peaking at 11.6 K |
| 1605 | Tower/Sorb = 13.1/10.8 K, MC/Still = 20/20 mW. IVC = 34 nbar |
| 1610 | Test: lower LN2 transfer stick into bath to cause a thermal shock. IVC peaks at 54 nbar then returns. Sorb rises to 11.7 K, Tower unaffected. looks like maybe tower cooling rate increased a bit after this test |
| 1625 | Tower/Sorb = 12.4/12.0 K, MC/Still = 20/20 mW. IVC = 34 nbar |
| 1625 | Open Turbo valve again to start pumping on IVC. Temperature starts increasing quickly. |
| 1635 | Tower = 12.5 K |
| 1640 | Tower = 12.7 K Close turbo valve again |
| 1645 | MB = 18.6% |
| 1655 | Fill LN2 cold trap full. |
| 2100 |  |
| hours ago | ||
|---|---|---|
| -12 | heaters off | no pumping |
| -10 | heaters on | no pumping |
| -9.1 | heaters on | pumping |
| -8.2 | heaters on | no pumping |
| -4.8 | thermal shock test | |
| -4.6 | heaters on | pumping |
| -4.3 | heaters on | no pumping |