2018/03/02 (Friday)
| Status: LN2 transfer yesterday, then found a blockage. Warming the fridge overnight, He gas in the cryostat vacuum jacket. | |
| 0920 | MC(Cernox) = 275.2 K, Sorb = >249 K, Cryostat surface = 22.1 C (lab 22.9 C), IVC = 6.3 mbar |
| Lab = 22.9 C, 22% rel humidity, so dew point = 273 K. We're a bit above that so we could lower the main bath if we want to. | |
| 0925 | Check contents of Trap 2 after yesterday's cryocleaning: 6.7 mbar of contaminants. Pump this out with scroll pump. |
| Cryocleaning log | ||
|---|---|---|
| date | duration (minutes) | contaminants removed (mbar) |
| Feb 27 | 55 | 13.5 |
| Feb 27 | 55 | 0.2 |
| Feb 28 | 140 | 4.5 |
| Mar 1 | 75 | 6.7 |
| 0930 | Quick electrical checkout on DIB2 |
|---|
DIB2 275K Electrical check:
- SQUID B and D were OK at 300K, but open/high at 77K. Now they are OK again
- Feedback coil B was open at 300K, then D was open at 77K. Now only B is open.
- QET B was open at 300K and 77K. Now it's still open.
- At 77K there was a 1 MΩ short from chassis to qI drain/source. Now it's gone again.
| We've decided to try to fix the apparent 77K short. | |
| 0950 | Fill IVC with N2 gas. |
| 1005 | Lower main bath. |
| 1015 | Erect clean tent around fridge. |
| 1020 | Check pressures in fridge: separately check LHe cold trap, condenser, still. None of them shows any measurable pressure on P1 or G1. (P1 went down slightly when still gate valve was opened). Pump out fridge for a couple minutes with scroll pump anyway. |
| 1030 | Open IVC |
| 1040 | Check the two opens on DIB2 that are present at 300K. Both show about 0.05 nS. The reading gets less stable if you squeeze the stripline connector and SQUET plug together. But the opens persist. Not bothering to investigate further. |
| 1100 | Throughput test at 280 K using same procedure as yesterday. 3He pump is on so all mixture in use, test through cold LN2 Trap 1. Let G1 rise to 600 mbar before Step 3, then it falls to 46 mbar, then rises steadily. Throughput 7.3 mbar/min. Similar to Run 64, 2017 Sep 18. |
| 1110 | Pump mixture to dump |
| 1125 | Tower is removed, in clean room |
| 1140 | Start cryocleaning mixture through LN2 Trap 2, V6 = 13.0% |
| 1150 | Increase V6→13.2% to reestablish flow |
| 1235 | Inspecting tower for clues about the DIB2qI short. One theory was that a wirebond on the side coax for the feedback resistor was touching the chassis. But this part of the side coax is not covered by the housing - it's just open to vacuum. So that can't be it. |
| 1245 | Another possibility is the wire in the side coax that leads to the FET gate. This is the second wire from the left. We removed the cover on the side coax and looked at this wire and its solder connections on both ends. Looks fine. Wire is well centered in trench. |
| 1255 | Another possibility is the tower face wire. Took one of the plates off the tower face - the wire looks fine. |
 |  |
 |  |
| We suspect that maybe the SQUET was plugged into the tower wrong, with pins not all in their sockets. All the wiring issues we saw, some at 300K and some at 77K, were with this DIB and could have been due to the SQUET connection. | |
| 1305 | Check SQUET ZC-36 on bench. The pB feedback coil is open unless you move around the SQUID card, then you see an intermittent conection. This one was OK at the BOB at 300K but open at 77K. Look at feedback coils: pB is open as seen at 300K. pA is reading too low, 1 MOhm instead of 20 MOhm. Check QET to return: pB is open, as seen at the BOB at 300K. |
| 1335 | Checked ZC-13 which was noted as bad on 2017/8/30 but was actually used after that in Run 65. One thing noted as bad was LED1, which is unlikely to break - rechecked this and it turns out it's fine. So we'll use this SQUET. |
| 1340 | Tower is reassembled. Same side coax arrangement as before. |
| 1345 | Tower electrical checkout, comparing to Tuesday. Problem: DIB1 qO Rfeedback is open, qI Rfeedback also open. |
 |  |
 |  |
 |
| 1350 | Fix both DIB1 ST-3-3 Rfb wirebonds. |
|---|---|
| 1400 | Increase V6 to 13.4% to reestablish flow |
| 1415 | Stop cryocleaning, pump mix back to dump. |
| 1445 | Remove Trap 2 from LN2 bath to let warm up |
| 1450 | Re-attach side coax ST-3-3 on DIB 1 with the addition of a kapton-coated copper sheet covering exposed the resistor and capacitor region. [Attach photo] |
 |  |
 |  |
 |
| 1458 | Tower electrical check passed, same as Tuesday. |
|---|---|
| 1450 | Start cryocleaning mixture through Cold Trap 1, V6 = 13.1% |
| 1505 | Increase V6→13.2% to reestablish flow |
| 1605 | Stop cryocleaning, pump mix back to dump |
| 1610 | Reinstalling tower, almost finished. |
| 1620 | Electrical check on DIB2: looks fine. SQUID A and Feedback pA are open, but those are known issues with SQUET ZC-13. |
| 1625 | Remove LN2 Cold Trap 1 from bath to let warm up |
| 1620 | Electrical check on DIB1: looks fine. |
| 1700 | IVC is closed, tightening the screws. Start gently pumping IVC with scroll pump. |
| 1720 | Quick leak check of IVC bottom indium seal. Looks ok. But background was 10,000 pbarL/s, so not very sensitive. |
| 1725 | IVC pumping pressure down to 76 ubar, start pumping with turbo pump |
| 1740 | Raised main bath. |
| 1740 | IVC pumping pressure = 0.86 ubar |
| 1800 | Check warm LN2 Cold Trap 2: 4.6 mbar. Pump out trap. |
| 1815 | Check warm LN2 Cold Trap 1: 10.0 mbar. Pump out trap. |