2016/09/06 (Tuesday after Labor Day)
| Status: fridge at room temperature, cryostat Dewar is down. Pumping on fridge lines with turbo pump through IGH vent, through vent speedivalve, V7, V2, V1&V3, Condenser speedivalve and Still gate valve. Mixture is in dump and 3He pump, manual dump valves are closed. |
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| On Friday a leak was detected from the dilution unit to the IVC. It was not seen at room temperature but it was seen at 77 K: with the leak detector on the IVC a large leak was detected when mixture was introduced into the fridge lines. | |
| 0715 | Turbo pressure = 4.0 nbar. P1 = 12 μbar. Turn on leak detector. |
| 0725 | Turn off LD again. I think I want to try the leak detector on the fridge lines, then let He into the IVC. To do this however I'll need to move the LD closer to the IGH, and reconnect the turbo pumping manifold to the IVC. |
| 0730 | With turbo pump valved out of fridge lines, IGH pressure drifts up to 2000 nbar. Alternately closing the turbo pump valve and the IGH vent speedivalve suggests that the increase is coming mostly from the fridge side, no leaks in the lines up to the IGH. |
| 0745 | With turbo pump pumping on fridge lines, pressure is 5.4 nbar. Closing V2 allows it to fall to 3.0 nbar. But leaving V2 open and instead closing the condenser and still valves doesn't cause the pressure to fall, it stays at 5.4 nbar. Interesting. |
| 0755 | With condenser and still valves closed, closing V3 causes turbo pressure to fall to 3.0 nbar; opening V3 again causes is to rise to 4.6 nbar. This suggests a leak into the still pumping line independent of the dilution unit. Could be through V6 from the 3He pump inlet, or could be from any of the flange connections. For now close still gate valve and V3, this isolates the still pumping tubing, we can watch for increase in P1 (currently 14 μbar). |
| 0810 | Move leak detector close to IGH and connect to hose leading to vent. Turn on leak detector. |
| 0815 | Reconnect turbo pumping manifold to IVC and pump out lines to IVC |
| 0820 | Open IGH vent speedivalve to begin leak checking fridge lines. Only V7, V2, V1 and condenser valves are open, still pumping side is isolated (still gate valve and V3 closed). So we're leak checking the fridge but the only connection to the still side is through the impedance. |
| 0825 | Open IVC valves to pumping manifold. IVC pressure is high, “>1 bar” according to turbo station gauge. Pump out with scroll pump. Sound from scroll pump suggests IVC pressure was much lower than 1 bar but not sure how low. |
| 0825 | Leak detector on IGH / condenser is at 160 pbarL/s and settling. Closing condenser speedivalve or V1 does not cause much of a drop. But closing V2 causes it to fall quickly. This suggests gas/leak in G1 volume. The G1 volume is connected to lots of other stuff. |
| 0835 | Begin turbopumping IVC |
| 0835 | P1 is drifting up slowly, now at 18 μbar. Open V3 to let the P1 volume (still pumping line) open to the LD: leak rises from 140 to 1600 pbarL/s. Close V3 again, leak drops. |
| 0840 | With V3 closed, opening the still gate valve does not cause much increase in leak. This should let the leaky P1 volume open to the LD through the impedance, but I guess this is too slow to be noticeable with the background around 200 pbarL/s. |
| 0845 | Turbo pressure = 340 nbar, close turbo valve. IVC pressure = 54 μbar. |
| 0855 | LD, pumping on condenser side, = 140 pbarL/s. Let 10 mbar of He gas into IVC. Leak signal does not change. Open still gate valve and V3. Leak increases to 1800 pbarL/s. Not a lot different than before. |
| 0900 | Leaving LD to pump on both sides of fridge. Begin pumping out IVC. |
| 0915 | Let He into IVC in units of one hose-length, watch LD as it pumps on both sides of fridge. First hose-length increases IVC pressure to 3.4 mbar, second to 19 mbar, third to “>1e3 mbar” on gauge. Let in a total of 15 hose-lengths. The mechanical gauge attached to the He feed indicates an IVC pressure of 2 inHg ≈ 70 mbar. Leak signal does not increase - over the full procedure it falls steadily from 1570 to 1360 pbarL/s. Either the leak from IVC to fridge is gone again at room temperature, or it is too small to see with this high a background. |
| 0920 | Begin pumping out IVC |
| Probably at this point it makes sense to put the LD back on the IVC, |
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| 0925 | Set up LD to leak check still pumping line through vent speedivalve, V2, and V8, all other valves closed. |
| 0930 | LD background = 1390 pbarL/s. Squirt around the three KF o-ring connections at the end of the copper pipe that leads from the pump alley. Leak increases, to 1470 pbarL/s. So this is one leak to the still pumping line. The clamp nearest the pump was the loosest, could tighten it a few turns easily. |
| 1055 | LD down to 600 pbarL/s. Squirt each of the three o-ring seals near the copper pipe. The one closest to the pump is the only one that causes an increase, to 905 pbarL/s. (later on the same flange saw increase from 856 to 1500.) Also check the o-ring seal near the gate valve, no increase seen. |
| 1100 | Close V2 and V8 and vent speedivalve. Open the still pumping line to air by disconnecting the leaky o-ring. Strangely P1 rose only to 75 mbar, maybe it reads differently for air versus helium. Clean o-ring and flange surfaces, grease o-ring a bit, reattach seal. When air was let into still pumping line, G2 (3He pump pressure) rose from 558 to 562 mbar, suggesting some leakage through closed V6 (or some more complicated route through IGH). |
| 1110 | Open V2 and V8 and vent speedivalve again, start leak detector to pump out still-pumping line |
| 1115 | Leak 4500 pbarL/s and falling. |
| 1120 | Leak 1500 pbarL/s and falling. |
| 1125 | Leak 800 pbarL/s and falling. |
| 1130 | Leak 630 pbarL/s and falling slowly. |
| 1135 | Leak 558 pbarL/s and falling slowly. |
| 1140 | Leak 493 pbarL/s and falling slowly. |
| 1140 | Leak 440 pbarL/s and falling slowly. |
| 1150 | Squirt-test all connections to the still line in the pump alley. No increase in leak rate seen, stays at 430 pbarL/s. Close vent speedivalve, V2, V8. |
| 1220 | Connect leak detector directly to flange near still gate valve to pump directly on still side of fridge. Begin pumping on still with leak detector. |
| 1235 | Leak 6.3 pbarL/s. |
| 1255 | Leak 5.9 pbarL/s, looks pretty flat |
| 1300 | Let helium into IVC, in steps, up to a full atmosphere. No increase seen in leak. After leaving it a couple of minutes, looks like a slow increase may be occurring. |
| 1305 | Leak 6.7 pbarL/s |
| 1310 | Leak 6.9 pbarL/s |
| 1315 | Leak 6.9 pbarL/s. Start pumping out IVC again with scroll pump. Leak starts to go down immediately by a few tenths. |
| 1320 | Leak 6.0 pbarL/s |
| 1325 | Leak 5.8 pbarL/s. Stop pumping IVC. Fill IVC with helium again. Fill up to 1 atm. After a minute start to see leak creep up. |
| 1330 | Leak 6.6 pbarL/s |
| 1340 | Leak 6.7 pbarL/s |
| so it is repeatable, we see a slight (and somewhat slow) increase in still leak rate when the IVC is filled with 1 atm of helium. | |
| 1400 | Put up clean tent in preparation for opening IVC |
| 1500 | IVC is open and 4K stage removed |
| 1530 | Tower is removed. Leak 5.4 pbarL/s, drifted down after opening IVC, probably most of the helium has diffused out |
| 1605 | 30mK can is removed. |
| 1620 | Lower 4K can removed. Commence removing 100mK can. |
| 1635 | Spool removed and placed anteroom. Six mixing chamber screws are visible. Prepare for spray test with background rate of 5.1 pbar*L/s. After 3 minutes the leak rate has steadily risen to 5.3 pbar*L/s and appears to be rising more. Stop spraying. Two minutes after we stopped spraying (five minutes after the start of the test) the leak rate is still at 5.3 par*L/s. |
| 1730 | Reattach spool and hang bucket with one lead brick from the spool, and perform leak check with background rate of 5.0 pbar*L/s. After three minutes of spraying the leak rate had slowly risen to 5.15 pbar*L/s. After a few minutes the leak rate is at 5.10 and seems to be decreasing. |
| 1739 | Leak rate = 5.0 pbar*L/s. |
| 1745 | Tightened MC flange screws. Then noticed leak rate had risen to 5.3 pbar*L/s. Unsure if this was due to the tightening process or ambient He from sprayer. |
| 1747 | Close valve leading to wizard staff and flush IVC from top with N2. After a few minutes of flushing with N2, the leak rate remains at 5.2 pbar*L/s, after spiking as high as 5.4 pbar*L/s, though this could just be a random fluctuation. |
| 1758 | Conduct another spray test now that it's been flushed. Leak rate starts at ~5.17 pbar*L/s. |
| 1801 | Cease spraying after 3 minutes. No change in leak rate. |
| 1804 | Leak rate still low at ~5.13 pbar*L/s. |
| 1818 | Leak rate has dropped slowly to ~5.05 pbar*L/s, and it is uncertain if this is due to the tightening of the mixing chamber screws or flushing out the He with N2 gas. Tape a bag loosely around the open lines and stripelines for overnight and keep the leak checker on to “pump out” the fridge lines overnight. We can decide how to continue tomorrow. |