Today was another productive day in the high bay. Jeff and I started out by taking some CMM measurements of the half-wave plate system outside the cryostat to figure out reference positions for things like the optical encoder photodiodes. We then put the whole system in the cryostat to make some measurements of the HWP mount relative to the cryostat but then realized we went out of order -- we had to take those measurements first, without the HWP in the system, otherwise our reference points are obscured by the rotating part of the assembly. So, out it came, the rotor was removed from the HWP table, and the table was then reinstalled into the cryostat to do the measurements. Then the HWP table was removed, the HWP rotor reinstalled, and the first set of measurements we did was re-done.
I divided up my time by helping Kyle finish the assembly of the instrument. We first installed all the 1 Kelvin shielding on the optics box, a process which involves copious amounts of aluminum foil tape. Then, once that was done, the sub-Kelvin fridges were finally mounted to the cold plate and their heatsinking installed. Kyle did some final wire checks and the instrument was finally done!
Next comes more alignment -- this process involves installing the instrument into the cryostat and aligning the final lens which lives in the cryostat optics stack (the silver cylindrical protrusion atop the big blue cylinder of the cryostat). Then, we remove the instrument, the HWP system goes in for the final time, then the instrument goes back in for the final time, then we install SQUIDs and connect cables, close up the bottom of the cryostat, flip the cryostat over, make some final measurements with the CMM, put the window back on, make more measurements, and then...pump! Sounds like a piece of cake, right?