2013/10/26
| 1755 | Summary of work performed earlier today: |
|---|---|
| Blow out nitrogen. IVC pressure 2.2E-6 mbar, mixing chamber temperature 77.6 K, background helium leak rate 2.4E-8 mbar l/s. Helium leak rate rises gradually to 2.7E-8 mbar l/s during blowout implying no gross leak. Evacuate main bath and overpressurise with He-4 gas; no change in helium leak rate. The leak witnessed over the last couple of days appears to have disappeared… for now. | |
| Performed throughput test with Berkeley's method. This involves closing all valves on IGH, opening valve V13A to allow mixture in He-3 pump's exhaust to cool nitrogen cold traps, and then opening valve V9 to allow mixture from dump to enter nitrogen cold trap 1. This is followed by opening condenser line speedivalve and gate valve, and valve V1 while monitoring change in pressure on P1. Test was repeated twice and following results were obtained: |
| Table 1: Results from first throughput test. | |
|---|---|
| Time [s] | P1 [μbar] |
| 0 | 15 ± 0.5 |
| 30 | 20 ± 0.5 |
| 40 | 65 ± 2.5 |
| 50 | 140 ± 5 |
| 60 | 220 ± 5 |
| 70 | 300 ± 10 |
| 80 | 400 ± 25 |
| 90 | 450 ± 25 |
| 100 | 600 ± 25 |
| 110 | 700 ± 25 |
| 120 | 850 ± 25 |
| 130 | 1100 ± 50 |
| 140 | 1400 ± 50 |
| 150 | 1700 ± 50 |
| 210 | 3000 ± 100 |
| 240 | 3600 ± 100 |
| 270 | 4000 ± 250 |
| 300 | 4500 ± 250 |
| Table 2: Results from second throughput test. | |||
|---|---|---|---|
| Time [s] | P1 [μbar] | G1 [± 1 mbar] | G2 [± 1 mbar] |
| 0 | 16 ± 0.5 | 695 | 633 |
| 20 | 17 ± 0.5 | 687 | 626 |
| 40 | 60 ± 2.5 | 687 | 626 |
| 60 | 220 ± 5 | 687 | 626 |
| 80 | 380 ± 10 | 687 | 626 |
| 100 | 600 ± 25 | 687 | 625 |
| 120 | 850 ± 25 | 687 | 625 |
| 140 | 1200 ± 50 | 687 | 625 |
| 160 | 1700 ± 50 | 687 | 625 |
| 180 | 2200 ± 100 | 687 | 625 |
| 200 | 2600 ± 100 | 687 | 625 |
| 220 | 3200 ± 100 | 686 | 625 |
| 240 | 3600 ± 100 | 686 | 625 |
| 260 | 4000 ± 250 | 686 | 625 |
| 280 | 4000 ± 250 | 686 | 624 |
| 300 | 4500 ± 250 | 686 | 624 |
| A couple of things to note about the results in Tables 1 & 2: results are consistent with each other; and throughput rate is a factor of three worse than that at Berkeley. Of course, K100 is a different fridge, but this factor of three degradation would agree with throughput rates from the last two runs. | |
| Additionally, at time = 0 seconds in Table 2, G1 & G2 pressures should be the same as valve V1 has not been opened. However, G2 is lower than G1 by around 60 mbar. Unsure of reasons why. | |
| Fill IVC with 0.63 mbar He-4 exchange gas. Commence first helium transfer. | |
| 2005 | Mixing chamber temperature 10 K. Start pumping He-4 exchange gas out of IVC. |