2017/11/09 (Thursday)
| Status: 600 mK rod re-installed, fridge reassembly in progress. All mixture recovered to dump. 1K Pot needle valve closed. Trap 1 and fridge pumped out. Cryostat vacuum jacket pumped out. | |
| 0930 | More fridge work: polish top and bottom surfaces of MC spool, attach MC spool, wrap tower thermometer wire partly around spool (avoiding contact with 100 mK can and 600 mK rod), tape down to spool with kapton tape covered in loop of teflon tape, then tied down with dental floss. NOTE: originally used 7 steel screws for this, but I inadvertently used 6 brass screws - these were previously used to attach the lower 100 mK can. |
| 1010 | More fridge work: install stripline heatsink at roof of IVC. Photos from 2015 April 14 stripline installation were helpful. Polish bottom surface of upper 100mK can, polish top and bottom surfaces of lower 100mK can, install 100mK can. |
| 1025 | More fridge work: polish outside surface of lower 100mK can. This should help reflect some of the 4K IR radiation it receives from the IVC, decrease the load on the cold plate. |
| 1530 | More fridge work: Install middle IVC can, attach stripline buckle and heatsink at bottom of middle IVC can, attach stripline end cover plates, put up clean tent. |
| 1330 | Begin disassembling SQUID card on SQUET ZC-31 |
| 1350 | Bring SQUET ZC-31 to wirebonding lab to modify for DIB4 of G101c as per plan. |
| 1500 | Finish wirebonding modifications on ZC-31 |
| 1520 | Reassemble SQUET ZC-31 |
| 1555 | Electrical check on ZC-31 SQUID-card connections, all look OK. |
I'd noticed that the tower-side QET return to detector-side QET pins on the SQUET had resistances around 20 Ω, while other straight-through lines are more like 2 Ω. Also it looked like the return-to-bias seemed to be lower on the channels whose shunt resistances had been reduced. That makes sense because those lines contain the shunt, but it doesn't make sense because 20 mΩ or smaller should be negligible. Apparently at room temperature the shunt resistances are much higher.
Below is a table of before- and after-modification QET-to-return measurements for ZC-31:
| ZC-31 | Before modifications | After modifications | ||
|---|---|---|---|---|
| channel | Rshunt | QET-return | Rshunt | QET-return |
| pA | 20 mΩ | 23.6 Ω | 20 mΩ | 23.4 Ω |
| pB | 20 mΩ | 22.8 Ω | 0 mΩ | 2.6 Ω |
| pC | 20 mΩ | 25.4 Ω | 6.7 mΩ | 14.2 Ω |
| pD | 20 mΩ | 23.5 Ω | 6.7 mΩ | 13.7 Ω |
It looks like the the standard shunts are around 20 Ω at room temperature. That means the reduced ones here should be about 7 Ω, but actually they're reading around 11 Ω.