Run 42

Let's start with the good news. We managed to achieve our fastest cooldown yet, taking a mere 26 hours from the moment we sealed the IVC to the point we reached a base temperature of 65.4 mK. This just so happens to be the best base temperature we've achieved in months!

Now for the bad news… we can't find the Tcs. We tuned and locked the SQUIDs on DIB 3 (channel B's behaviour seemed to indicate a problem, but we ignored it for the time being and used the other 3 channels) and attempted to change the QET bias to determine if we had reached a sufficiently low temperature. We saw no signals, implying that the phonon sensors were still normal.

Therefore, we proceeded with plan B and attempted to measure the Tcs during a single-shot test. During our first attempt, we reached a base temperature of 45.9 mK before the mixing chamber started to warm up again. However, this was not sufficiently low enough to enter the transition region.

We saved a little time by collecting the He-3 we recovered during the signle-shot test in the nitrogen cold trap rather than the dump. This allowed us to try again shortly after our first attempt. This time we switched to DIB 2, and tuned and locked the SQUIDs. No problems were witnessed with any of the channels, although they still appeared to be normal as no peaks were visible when adjusting QET bias.

We reached a slightly lower mixing chamber temperature of 45.1 mK during our second single-shot test. However, the TESs did not enter the transition region.

This would imply that the Tcs lie below 45 mK or something is wrong. We'll conduct some Rn measurements later today, but I don't think there is anything else we can do with this crystal. Unfortunately, we cannot say that the Tcs are uniform for the proposal.

I would however like to thank everybody working in the laboratory for their commitment over the last couple of days to give us a shot. Both Allison and David stayed overnight on Wednesday and took over for me on Thursday afternoon/evening. Chris also deserves a mention as he stayed until 2 am on the day of one of his mid-term exams to clean flanges.

Many Thanks, Hassan