Happy Holidays!

Happy Holidays from the South Pole.  I've now been here working for over seven weeks, and this past weekend we celebrated Christmas, South Pole style.  The weekend before Christmas, some of us helped our amazing baker cutout enough Christmas cookies for the entire station (that's about 140 people right now).  In case you were thinking that making cookies for your family was a lot, this was a lot of cookies (and I didn't even have to make the dough).  We also decorated gingerbread houses.  You can see mine with a very impressionist rendering of the SPT on the roof.

Me and my SPT gingerbread house (only tilting a little).

Christmas eve started out with caroling over the HF radio link to the other stations on continent.  Personally, I think South Pole was the best, since we were accompanied by an acoustic guitar.   All of the stations also exchange Christmas cards.  I took a picture of just a few of them.  If you look closely at the one from South Pole, you'll see some familiar people!

After spending the afternoon working out at the telescope, we came back to Christmas dinner.  Just like Thanksgiving, this is a really nice event with some really lovely food.   First there were appetizers (baked brie and bruschetta), then dinner with beef wellington and lobster.  Finally, desserts from around the world!  And of course, what would dinner be without a roaring fire to gather around?

After dinner, there was a live band that played a few songs (lot of talented people here) and big dance party in the gymnasium.

The big event on Christmas day itself is the  Race Around the World.  The course is two miles outside.  It started at the geographic pole went out to the SPT and IceCube experiments and then looped back around to the station and the pole.  Prizes are given to the fastest male and female runner, but also for the best costume.  This year's winner was dressed as Tigger. After the race it was into the station for Sunday brunch and then back to work at the telescope!

When Optical Benches Fly

Building up the receiver is not the only work that has been going on at SPT the last couple weeks.  There has been a separate team of people working on installing new optics.  We have a brand new optical bench and two new mirrors that bring the light from the primary dish into the receiver.  The optical bench is shown in the picture below, with the front surface of the secondary mirror showing.   The mirrors themselves are pretty special as they are machined from single pieces of aluminum.  The secondary mirror is a little over a meter in diameter.

The new SPT-3G optical bench before it was installed.

The entire optical bench & mirrors are also covered with the little black and white pieces of paper.  These are actually targets used in a process called photogrammetry.  The idea idea is that you take many pictures of the mirrors and the bench from different angles.  You calibrate the position of the camera, and a computer program then determines exactly how the mirrors are lined up and if they need to be adjusted. Now that the mirrors are aligned, someone will have to take all the targets off and clean up the surface.

The SPT-3G secondary mirror.

The other fun thing to notice is that our mirrors are not as precise as optical mirrors and the surface is rougher.  That is just fine to longer wavelength millimeter light.  You can still see your reflection in the surface of the mirror, but it is very blurry.

My reflection in the SPT-3G mirror.

The next step is actually installing the entire bench into the telescope. It sits at the top of the boom arm, right under where the person standing on the telescope is.  The team doing this had to remove a bunch of panels from the receiver cabin, pull out the old bench and some supports, and then put the new bench in.  The particular day this picture was taken was the day of installing the new bench.  You can judge how much help was needed based on the number of snowmobiles parked out front.

Snowmobile-jam!

Once the cabin was ready, it was time to lift the bench into the telescope using the crane.  First it came out onto the porch of the tent it was in, and then was lifted off the ground, swinging up and around until it was lined up with the hole in the receiver cabin.  It was pretty impressive to watch the entire operation, given the necessary precision of the crane operation.

The optical bench as it is first lifted off the ground.

Up and away.

Coming into the cabin.

All lined up and almost in place.

As soon as the receiver was assembled we turned on the vacuum pump, and then the mechanical refrigerators that cool the detectors down to 0.25 Kelvin.   It took about a week of continuous cooling to get there.  During that time, we were also working on assembling the external readout electronics.  In the picture below, the control electronics for the detectors are in the box on the upper right of the cryostat.  Now that the detectors are cold and the electronics are in place, we've begun turning on everything and trying to understand the performance of the receiver.

Almost a full receiver now that it has electronics!

The other major accomplishment last week was testing the mechanical fit of the receiver into the cabin.  The whole thing weighs somewhere upward of 2500 pounds and gets lifted up by 4 chain hoists until it mates with the optical bench.  With the bigger new cryostats, the fit is really tight, and it is a delicate dance of careful lifting to make sure nothing collides.  

Prepping for the lift.  The first chain hoists are attached and the receiver was tilted into the vertical position.

 

Just barely lifted out of its cart.

Part way up.  You can see it looks like it is at an angle.  This is to keep a part on the side of the receiver from colliding with some wiring on the cabin wall.

It fits!

Getting it up took all afternoon.  After a break for dinner and some more quick checks for fit and alignment, we spent the evening bringing it back down so we could continue detector testing. All in all, a  pretty wild day.  At the end of it, I captured some of the team as they were winding down.

They are actually happy everything worked, just tired from operating chain hoists for 8 hours.

Building SPT-3G

It's been an extremely busy week, but the new SPT-3G camera is now built and ready for our first set of tests here at pole!   The last of our cargo arrived a little over a week ago, and as soon as we had it out of the crates it was a race to assemble as quickly as possible.  We are only planning on one short test run of the new camera before we have to work on it some more to finalize the configuration for the Antarctic winter.  I work mainly on the focal plane, the structure that houses the detectors and  electronics.
 
First, the two modules I showed in my last post get inserted into the structure seen in the picture below.  You can see the other eight silver hexagons where our other wafers will go.  Right now, these spots are blanked off to prevent light from leaking onto the detectors in the middle in a strange way. 

The SPT-3G focal plane before it was installed into the cryostat.

The rest of the focal plane looks complicated but really is just a set of supports.  Our detectors operate at a temperature of 0.25 Kelvin (about -273 degrees Celsius).  The focal plane structure is designed to help us keep that cold temperature.  We use carbon fiber rods to isolate the ultra-cold stage that the detectors mount on, from pieces that run at other temperatures (between 0.35 to 4 Kelvin).   Finally, there is a sheet of aluminized mylar (looks like tin foil between different metal pieces) that we put into place to prevent radio frequency (RF) noise from getting behind the detectors to the electronics.  The aluminum on the  mylar creates a continuous metal sheet that the RF can't penetrate.  Installing this sheet is one of the most tedious parts of the assembly, as the mylar is delicate and a single pinhole would ruin the effect.  Luckily, Joshua (UChicago grad student who also works on the focal plane assembly) and I have steady hands.

Next we take the entire focal plane and install it into the the cryostat.   The lenslets face towards the rest of the optical elements, so you only see the backside of the focal plane from here on out.  Inside the cryostat are also the two mechanical refrigerators (out of sight in the pictures below) that cool the focal plane down, and some additional electronics (bottom of the picture).

The backside of the SPT-3G focal plane after install.

Me, the focal plane, and the cryostat.

 Once everything was plugged in and checked out, we closed up the cryostat.  There are three layers of shells to put in place.  The inner two (see one below) help shield the cold focal plane from hot objects around it.  The heat radiated from the room temperature outer shell would completely overwhelm the refrigerators and we wouldn't be able to get cold otherwise.

First of the shields on the cryostat covering the view of the focal.

In parallel to the work on the focal plane,  there was another crew of people assembling the optical elements (lenses & filters) that the camera looks out into on the other side of the cryostat.   We ended up finishing up around midnight last Saturday.  The very happy crew is below.

The receiver assembly crew and the completed SPT-3G instrument (that big metal thing in the back).

Now we are waiting for the refrigerators to do their job and cool the cryostat down.  It is a big instrument, so we're estimating it will be done sometime late this weekend.   Once it's there, we'll start turning on and tuning up the electronics and detectors for what will hopefully end with the first light of SPT-3G.

In other news, the first South Pole Overland Traverse (SPOT) arrived yesterdays.  These are a group of seriously awesome tractor drivers that drive from McMurdo to the South Pole to bring us fuel.  It's much more efficient than bringing it on the planes. I don't have any pictures yet, but there are some in posts from past years.   Also, someone has been anonymously sending a member of SPT five-pound bags of gummy candy.  Whoever you are, thank you.  You have now fueled many late nights working at the telescope and played a critical role in this first setup and cooldown. 

A portion of the current combined stash.