2021/03/29 (Monday)
- Lab in-person: Matt
- Virtual partner: Zach
| Status | Run 74 in progress. Warming the fridge to fix short and presumed thermal touch. DCRCs off, disconnected. All mixture in dump. 1K Pot isolated. Helium gas in IVC and cryostat vacuum jacket. All IGH and external fridge valves are closed. MC and Still heater @ 20 mW |
|---|---|
| 1300 | Matt enters lab. |
| 1305 | Turn off MC and Still heaters. |
| 1305 | Check pressure in IVC by opening check valve at top of fridge and holding finger over the end. It's somewhat overpressured. Leave the valve open for a minute to let out the overpressure, then close it again. |
| 1305 | Cryostat Vacuum Jacket = 0.22 mbar. Pump it out for a bit, first with scroll pump then after it gets below 0.1 mbar switch to turbo. |
| 1305 | MC(Cernox) = 286.7 K |
| 1315 | Derek closed the main recovery valve on the side that goes out to the liquefier system. This works but we usually close the recovery valve nearest to the main bath, above the LN2 Dewar. I closed that one and opened the main one. No change in the recovery meter when I did this. |
| 1350 | Turbo on Cryostat Vacuum Jacket = 0.34 μbar. With Turbo valved out for 1 minute, Cryostat Vacuum Jacket = 22 μbar. Stop pumping it now so I can drop the Main Bath - but we'll certainly want to pump it more before cooldown. |
| 1415 | Finish removing all Main Bath bolts. |
| 1420 | Remove covers from pit. Used the long 2×4 and slid it into the two handles to keep the cover from falling. Wore gloves because it's easy to get a splinter working with that board. |
| 1435 | While lowering Main Bath, stop to deal with a broken bolt that's sticking out of one of the holes, we broke it last time we raised the main bath. Got help from Mike Rother. It was so badly cross-threaded that he couldn't turn it with vice grips. Instead he knocked at it with a hammer to break it off. |
| 1505 | Finish lowering Main Bath into pit |
| 1510 | Put covers on pit |
| 1520 | Erect clean tent at bottom of fridge and turn on HEPA filter fan |
| 1525 | Clean dust off inside of clean tent with wipes and methanol |
| 1540 | Remove IVC bottom |
| 1555 | Attempt to reproduce DIB2 qI Feedback - to - Chassis short by pushing on various bits around the SQUET, interposer, stripline. I can't reproduce it. But it is definitely the case that the SQUET flyover cable is pushed up against the shell of the stripline plug. There's some kapton tape on the flyover cable meant to prevent cutting in and shorting the wires, but we could do this more carefully/thoroughly. I was able to produce a short by touching some copper tape to the outer side of the SQUET, where the pin ends are exposed. But there's nothing close to here that could have produced that short. |
| 1615 | Detach 4K heat sinks and remove both SQUETs and interposer from Tower. (still attached to striplines.) |
| 1625 | Remove 3 tower socket cover plates. Remove 4K stage. |
| 1630 | Examine 100 mK stage for possible thermal touches. The copper tape that partially covers the hole in the 100 mK stage that the 600mK rod goes through was touching the 600 mK rod. This could cause the type of thermal short we saw, because the coldplate temperature was elevated, and the still temperature was fine, maybe a little low. Also saw that the tower-end of one of the 100mK heat sinks was crooked so that it was touching the outside of the tower. This is also contact between the 100mK and 600mK stages, because that outside part of the tower is the 600mK stage of the tower. (The 100mK stage of the tower is entirely internal except for the ears.) |
| so these possible thermal shorts can be fixed now. Could there be other shorts? Another possibility is that the tower thermometer wire which is taped down to the 30mK stage has come loose and is in contact with the inside of the 100mK can. Could this cause the symptoms that we saw? Need to look over the symptoms again… | |
| 1650 | Matt exits lab |