Cooldown A

     Sorry about the lack of posts!  It’s been a really busy couple of weeks.  When last I wrote we had just closed up Black Cat for the first cooldown, or Cooldown A.  Since then the cryostat was pumped down and cooled, then tested for several days, then warmed back up and brought to atmospheric pressure, ripped open, pulled apart, reworked, put back together again, and Monday night we finally got it closed and on the pump for Cooldown B.  I’ll try to cover the highlights…

     Cooldown A started late on Friday December 23.  With almost nothing to do but wait for Black Cat to get cold we had our first day off in almost a month on Christmas Eve.   We slept in, ate brunch, then watched a couple movies – Indiana Jones and the Last Crusade and Primer – before getting dressed up in nice clothes for appetizers and Christmas dinner.  Christmas dinner was pretty special.  They decorated the galley and closed all the windows to make it dark.  All the tables were done up with nice table clothes, and there was fancier dishware and candlelight.  The menu was pretty awesome too – some amazing scallops, duck confit on fancy crackers, smoked trout, and New Zealand brie in puff pastries for some of the appetizers, and then beef wellington and lobster tails among other things for the main course.  The desserts were pretty awesome too.  I had entirely too much to eat but it was all just too good.

Just about everyone, including the galley, was dressed up nicely for Christmas dinner. I miss wearing ties.

Christmas dinner. Lobster tails at the Pole. Swanky!

The full Christmas dinner menu. It was pretty stellar. Great job, everyone!

     After dinner there was a dance party in the galley.  I watched for a bit, (dancing isn’t normally my thing), so I took off to the instrument room and practiced my clarinet for an hour.  It had been months since I practiced and it was nice to use it since I had lugged the thing all the way down here.

     On Christmas day we were back to working.  I won’t go into too much detail here, but after several days of testing we discovered some thermal problems with the system, but mostly in the secondary cryostat.  We stopped the cooldown and took the evening off on Tuesday before starting a pretty grueling week of reworks.  We had a group sauna to relax and headed out to the Pole again.  I was feeling a little silly and daring and somebody dared anyone in the group to stick their tongue on the pole marker.  Well… I did.  Just a quick touch and back off.  Unfortunately, I left a bit of tongue on the marker… about a quarter-sized chunk several skin layers deep.  I promptly scraped what remained of my tongue off the marker with my thumbnail.  People told me later they thought I had joked about actually putting my tongue on the marker.  They saw the pole move with me as I pulled away and they thought that meant I had pulled it away with my hands.  Nope.  My tongue pulled it away.  Luckily, the damage wasn’t too severe.  My tongue was totally back to normal in a few days.  It felt like a mild coffee burn while it healed.  But, I’ll tell you what – I don’t recommend doing that.

     The rest of the week was one 14-16 hour day after another, culminating in a pretty massive group effort very late Monday night.  Most of the reworks were in the secondary cryostat, which I wasn’t a part of, but we had several fixes to make in the camera itself.  We added more pixels at 90 GHz, swapped out an old 150 GHz wafer for a new one that should work a bit better, and fixed our readout electronics to let us see more of the detectors in the focal plane without confusion.  10 days after closing up the first time, at 4:15 AM Tuesday the 3^rd, we finished the modifications and mated Black Cat with the secondary cryostat for the second time.  If all goes well this might be the very last cooldown, which means we could stay cold until this time next year.  Fingers crossed!

Opening the receiver after Cooldown A. Readout striplines everywhere!

The fully populated SPTpol focal plane. 588 pixels at 150 GHz, 176 pixels at 90 GHz.

The receiver team with the camera before putting filters, RF seals, and heat sinking brackets on. Best receiver team EVAR!

     I’ll tack on to this post some awesome photos of the telescope and a truly remarkable sundog.  Workers have been adding a guard ring along the perimeter of the 10 meter dish as a shield to block out light that will mess our data up.  The guard ring and backing structure for the panels make the telescope even more impressive.  Finally, a sundog is a phenomenon much like a rainbow caused by hexagonally shaped ice crystals in the air.  It makes a ring around the sun with brighter points, and for really good ones you can see a ring surround you too.  We had one of those in the past week.  The pictures below just don’t do it justice.

The 10 meter primary mirror of SPT with the newly installed guard ring on.

The second sundog I've seen since coming down. There was a ring around the sun, as in the picture, and then a ring that surrounded me around the sky coming off the left and right bright spots. Pretty incredible.