A lot of things happened tonight (mostly in the realm of setbacks followed by recovering frome them), but the take-home is that the measured Q of my silicon sandwich clamp seems consistently lower when measured in the cryostat, compared to in the new chamber from the gyro. Here's a rundown of what happened today/tonight:
- Before dinner, I made a first measurement on the silicon sandwich idea (cantilever sandwiched between a couple spare pieces of silicon on each side --- see CRYO:1200). This gave me the highest room-temperature Q I've measured yet at ~6800.
- After dinner, I wanted to port this to the cryostat and potentially do a cooling run. Unfortunately, to fit it in the cryo volume, I had to flip the sandwich around so that it was protruding from the clamp in the other direction (for the first run, I had it sticking out over the power resistor to avoid clamping in the region on the other side that has the groove for the Glasgow-style cantilevers, but there wasn't enough room for that orientation in the cryostat, so I had to flip back---I made it work so I didn't clamp over the groove anyhow).
- Unwittingly, I made the dumb mistake of not first testing this freshly-clamped system again in the simple chamber, and after I closed the whole cryostat again and pumped down, I measured a much lower Q (back down around 3000).
- So, I opened the cryostat again, and then spaced out and made the further mistake of still not testing this apparently bad clamp job in the simple chamber, just to verify that I got the same low Q. Instead, I went straight to cleaning all the pieces and re-clamping.
- This time, I put it into the simple chamber and immediately recorded a high Q around 7000 again.
- This is when some setbacks kicked in:
- In opening the chamber, one of the RTD wires came loose from the feedthrough.
- Not realizing that these were just press-fit sockets, I unscrewed the feedthrough to have access so I could reattach the single loose wire, only to have several others fall off.
- So, I disconnected all the wires, spent some time mapping which one went where, re-soldered some and re-kapton shieled all, then reattached all wires, bunch taped them and taped the bunch to the feedthrough so that none could easily come loose. I also took this time to resolder the ESD wire that I broke the other day.
- In moving stuff around, I accidentally tugged on the ribbon cable between the QPD and its vectorboard readout circuit, pulling a couple connections.
- So I spent some time fixing that
- Now I was ready to do science again, so I transferred the (known good) clamp from the simple chamber back into the cryostat and carefully closed it all up again.
- After seal and pumpdown, I again measured a low Q around 3000.
So, it seems that the Q is repeatably lower for a particular clamp in the cryostat vs. in the simple chamber. To be sure, I'm going to do the final step of returning the clamp back to the simple chamber tomorrow and see if I again get a higher Q.
I'm not exactly sure why this could be happening. The only mechanical differences from one chamber to the other are:
- The clamping block is screwed via holes in the PEEK base to the cold plate in the cryostat, while it is dogclamped to the breadboard in the simple chamber.
- In the cryostat, there are wires soldered to the power resistor attached to the clamping block as well as a wire-attached Pt RTD kapton-taped to it. None of this is present in the simple chamber.
I'm tempted to think that (2) could be causing some excess damping, so one thing I will try is simply not connecting these just to see if that makes the probem go away.