I started cooling down the cryostat this morning. In preparation I had flooded the inner volume with helium yesterday and let it sit overnight while pumping on the outer volume to check if the seals on the inenr viewports are still intact after several cold cycles (these are viton seals, after all). When checking the next morning, the pressure had increased by ~50% (since the volume wasn't pumped), so it looks like the viewport seals are still good. I pumped on the inner volume briefly to bring it down to ~1e-5 torr (starting pressure was 4e-6 torr) and re-flooded with only helium to ~1e-2 torr. Liquid LN2 was added at ~10am. After ten hours the cavity can temperature was passing 180 K, and I expect them to have passed 123 K in the morning, at which time I will turn on the heaters with target temps of 120 K to leave some room for the heating from the average visible laser power.