The SPTpol Receiver is open!

This weekend we were very busy; we opened up the receiver, made several small fixes, closed it back up again, and just started cooling down again yesterday. This post will take you through that whole process.

After opening up the receiver the first thing we wanted to do was take out the focal plane. We knew we wanted to replace one (of seven) module of 150 GHz (2-mm wavelength) detectors, but still wanted to inspect it to see if we could find an obvious problem. We did not, so Jason swapped it out for the spare detector wafer. We also wanted to replace two of our four focal plane infrared filters, to increase the bandwidth of light that we are sensitive to, which ultimately improves our sensitivity.

While the most glamorous part of the re-work was the focal plane, which is also what most of my post is dedicated to. Jay and I were primarily working on the receiver cryostat, installing a new lens filter, and modifying the focal plane baffle to fit with the new parts. In addition, we replaced 1/6 of our SQUIDs, in attempt to fix some bad readout channels that didnt work, and are switching over to a more stable feedback algorithm which should bring back a couple dozen of our detectors.

Late Monday afternoon, we got the receiver and optics cryostat re-attached, and soon started pumping them down; we need to get the crysotats to a pressure about 100 million times less pressure than atmospheric pressure. Then on Tuesday afternoon, we turned on the pulse tubes and started cooling the cryostats down.