| 0815 | Have been searching for source of short during the night. No short witnessed when isolating stripline, SQUET card and tower from each other. It is only when the SQUET card and stripline are attached to the tower do we witness a short. |
| | The short appears to be capacitive rather than resistive in nature: the resistance increases with time when measuring with our multimeter, which would seem to indicate that we are charging a very large capacitor. Additionally, there is a potential drop across the shorted channels (QET bias, QET return, Qi & Qo bias) and ground. |
| | During investigation, some pins on the ebox feedthroughs were found to have resistances of ∼100 MΩ to ground. Flooding the sockets with methanol, wiping with a paint brush and blow drying with nitrogen gas was found to be an effective way to increase the isolation of these pins from ground. Unfortunately, this did not appear to have an effect on the short. |
| | Stripline 20 & SQUET card ZC-28 on DIB 2 have additional shorts between SQUID bias B, C & D to ground, and Feedback B & C to ground. This is probably not surprising, as SQUET card ZC-28 failed SQUID isolation tests as documented in SQUET elog entry 967. It is thought that these shorts will clear up at lower temperatures. |
| | We have decided to attempt to cool down anyway. We are out of time, and if it doesn't work, we can warm up and more thoroughly investigate the problem next week. |
| | Start evacuating IVC. |
| 1230 | Fill N2 cold trap full. |
| | Fed Cricket. |
| 1235 | Commence spray test. Background helium leak rate 6.3E-9 mbar l/s, rising slowly. Leak check 4 indium seals and ebox connector flange. Helium leak rate 6.9E-9 mbar l/s: no gross leak. |
| 1345 | Raise dewar and evacuate main bath. Evacuate 1 K pot. |
| | Cryocleaning of mixture has stagnated. Open valve 6 to 13.2%. |
| 1355 | Background helium leak rate 9.5E-9 mbar l/s. Overpressurise main bath with He-4 gas. Helium leak rate 1.1E-8 mbar l/s: no gross leak. |
| | Under vacuum, short between QET bias/return and ground has higher resistance (conductivity = 9 nS). It still behaves like a capcaitor. Not sure what this means. Perhaps an encouraging sign… |
| 1405 | Fill IVC with 10 mbar N2 exchange gas. Commence nitrogen transfer. |
| 1605 | Nitrogen level meter resistance 1.35 kΩ. Nitrogen transfer complete. Attach ping-pong ball. |