2019/05/10 (Friday)
| Status | Warm after hitting fridge blockages, 3 times. Found a leak in still pumping line yesterday and fixed it. |
|---|---|
| Setup | DIB1/3/4 → 3.2 MHz filters 2/3/1 → cable 3/1/2 |
| 0900 | Still pumping line (P1) crept up from 0.040 mbar to 0.075 mbar overnight. That's probably pretty good. |
| 0900 | MC(Cernox) = 284.5 K |
| 0900 | LN2 Trap 1 is warm. Check contents: 9.8-1.3 = 8.5 mbar on G1. Pump out with 4He pump. |
| 0900 | LN2 Trap 2 is warm. Check contents: actually not sure because I forgot to valve out the pump. Greater than 2.5 mbar. Pump out with 4He pump. |
| 0910 | Fill LN2 cold trap bath |
| 0915 | Cryostat vacuum jacket = 25 mbar. Begin pumping it out with scroll pump. |
| 0920 | Start cryocleaning mixture through LN2 Cold Trap 1, V6 = 12.4% |
| 0925 | Increase V6 → 12.8% to restart flow |
| 0940 | Increase V6 → 12.9% to restart flow |
| 0940 | Scroll pump on cryostat vacuum jacket = 30 μbar. Switch to turbo pump. |
| 0950 | Increase V6 → 13.0% to speed up flow |
| 1020 | Stop cleaning through Trap 1 after 60 min. G2 flow pressure was 570-710 mbar. Pump mixture to dump. Removed 9.4 mbar. |
| 1035 | Start cryocleaning mixture through LN2 Cold Trap 2, V6 = 13.0% |
| 1050 | Increase V6 → 13.1% to speed up flow |
| 1145 | Stop cleaning through Trap 2 after 70 min. G2 flow pressure was 570-705 mbar. Pump mixture to dump. Removed 1.6 mbar. |
| 1210 | LN2 Trap 1 is mostly warm. Check contents: 11.1-1.7 = 9.4 mbar on G1. Pump out with 4He pump. |
| 1230 | Start cryocleaning mixture through LN2 Cold Trap 1, V6 = 12.8% |
| 1245 | Increase V6 → 12.9% to restart flow |
| 1255 | Increase V6 → 13.0% to speed up flow |
| Interesting detail: when the flow is sped up enough to increase the G2 pressure significantly, sometimes G1 goes a little down, sometimes it goes up. In the first cleaning today (Trap 1) it went down a little. In the second cleaning (Trap 2) it went up a chunk. In the third cleaning (Trap 1) it again went down a little. Not sure what this means. Later: in the fourth cleaning (Trap 2), it went up a chunk again. The traps seem to behave differently. |
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| 1330 | Stop cleaning through Trap 1 after 60 min. G2 flow pressure was 575-625 mbar. Pump mixture to dump. Removed 8.3 mbar. |
| 1340 | LN2 Trap 2 is mostly warm. Check contents: 3.3-1.7 = 1.6 mbar on G1. Pump out with 4He pump. |
| 1400 | Start cryocleaning mixture through LN2 Cold Trap 2, V6 = 13.1% |
| 1500 | Stop cleaning through Trap 2 after 60 min. G2 flow pressure was 580-820 mbar. Pump mixture to dump. Removed 5.6 mbar. |
| 1505 | Turbo on cryostat vacuum jacket = 19 nbar. Close off pump for a few minutes: cryostat vacuum jacket = 250 nbar. Good enough, stop pumping out vacuum jacket. |
| 1515 | LN2 Trap 1 is mostly warm. Check contents: 10.1-1.7 = 8.3 mbar on G1. Pump out with 4He pump. |
| 1520 | IVC = around 0.3 bar. Start pumping it out with scroll pump. After 10 minutes switch to turbo pump. |
| 1545 | LN2 Trap 2 is mostly warm. Check contents: 7.4-1.8 = 5.6 mbar on G1. Pump out with 4He pump. |
| 1555 | Trap 2 is pumping down more slowly than earlier warm pumpouts. Maybe it's still warming up. |
| Another observation: looking closely, each time I pumped out warm Trap 1 today, it pumped down to about 2.2 mbar. The first time I pumped out warm Trap 2, it got to 1.7 mbar. So, maybe Trap 1 has a leak. It seems to behave different from Trap 2 in three ways: 1) during cleanings, G1 goes down when G2 goes up (opposite with Trap 1); 2) during warm pumpouts, it looks like Trap 2 gets to a lower final pressure than Trap 1; 3) today both the amounts removed from Trap 1 cleanings were larger than both the amounts from Trap 2 cleanings. The first Trap 2 cleaning was much better than the second - maybe before the second one, Trap 1 let a lot of air in? Hard to know, the data is not super clear. |
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| 1605 | Trap 2 is only down to 2.7 mbar. But it's flattening out. Maybe the gauge is behaving differently. Although just 20 minutes ago it got down to 2.2 mbar when pumping out Trap 1. I don't friggin know. |
| 1620 | Actually, maybe Trap 2 was warmer than usual. I had it sitting in a bucket of hot water. I changed it to a bucket of cold water, and the pressure fell, from about 2.7 to 2.2 mbar. |
| 1625 | Check pressure in Trap 1: 2.6-1.8 = 0.7 mbar. So it crept up a bit over 45 minutes. Pump it down for a bit, then leave it open to G1, we'll monitor how fast it rises overnight. |
| 1740 | Trap 1 (G1) = 1.3 mbar. It has actually gone down from about 2.7 mbar. Seems to be settling. Maybe the trap is absorbing gas from the IGH?? Dunno. Barometric pressure has dropped a little today - peaked at around 13:00 and has been falling since, down by about 3 mbar by 17:00. That would have something to do with it, though G1 seems to have fallen more quickly. |
| 2359 | Trap 1 (G1) = 1.5 mbar and quite flat. |
| So there's no evidence from watching the pressure that Trap 1 has a leak. And considering the variation in pumping pressure with temperature that I observed, the differences in warm pumpout pressure between the two traps the first three times are probably not meaningful. The different amounts of contaminants removed are frustratingly random, and even if there's a difference between the traps that doesn't necessarily indicate one trap is leakier - could be that one trap is more efficient. The differences in the G1/G2 pressure changes during cleaning do seem real, and indicate something. There was concern in the past that Hassan's aggressive heating of the traps with the heat gun could damage them (maybe melting the filter material inside or something), so maybe one trap was damaged more than the other and behaves differently. | |
| The G1/G2 behavior definitely suggests that during a cleaning, Trap 1 imposes a greater impedance to the flow than Trap 2. Is that good or bad? If the differences in the amount of contamination removed are meaningful, it may mean that Trap 1 is more efficient at removing contamination, and Trap 2 isn't doing a very good job. Note: G1 rising when G2 rose was first noticed a week ago, during two different Trap 2 cleanings (and not during the Trap 1 cleaning between them). |
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| An idea for a test: let a controlled amount of air into the trap while cold. Let it settle, record the pressure. Then warm up and pump out. Do this with each trap and compare. A more efficient trap should pull the air down to a lower pressure while cold. |