First Light and the First Signs of Winter

So last week we managed to get first light on SPT-3G!  The picture on the laptop shows the very first map of our calibration source (RCW38,  an ionized hydrogen region in the Milky Way).

Me & the very first map from SPT-3G. 

 

 

 

 

The SPT-3G first light map.

Since then, we've been working on getting the best performance possible out of the receiver, and making sure our winter personnel are up to speed on how things work.  Over the past few days, the temperature and windchill have dropped significantly.  It seems like this is a real change in the weather as the South Pole heads towards the winter season.  The last flight out of the station leaves on Feb 15, after that there are no flights until November.  My flight out is scheduled for tomorrow, so this will likely be my last post from the South Pole this year.  If everything goes to plan, on Saturday I'll be warming myself in the Christchurch botanical gardens.   From there I'm traveling a bit in New Zealand and then on to Fiji with some polar friends.

Leisure Options at the South Pole

So far, all my posts this year have been focused on building SPT-3G and the project.  That's a pretty fair summary of how I've been spending my time.  We've had a huge amount of work to accomplish and a very limited window to do it.  But once in a while, we do get time for some fun and relaxation.  So that brings me to leisure options at the South Pole.  

South Pole station is small, but it actually has a lot of options for time off.   There are a lot of activities, each organized by someone in the community.  This won't cover all of them, but includes a few of my favorites.   For example,  every Wednesday I try to go play volleyball.  

The wall of activities.

In addition to the big gym (where volleyball is) and a cardio/weight room (which I have been to exactly once to watch someone else work out while eating ice cream), there is a small climbing gym.  I am not a climber.  But I am told by people who are that it is pretty great for the small space.  Two of my co-workers, Kyle and Jessica, convinced me to come out with them to the climbing gym.  It's in its own little container building (heated) and smells a bit like socks.  But the floor is padded and they helped me set a 'beginner' route to try.  I will probably never be a climber based on my performance on this route, but it was a lot of fun.

The inside of the climbing gym.  Lots of routes!

 

Kyle spotting as Jessica rocks it!

Another activity that I have enjoyed is tourist watching.   Throughout the summer there have been many tourists that come through South Pole. That's right, for the low low price of about $50k per seat, you too can go to the South Pole for a few hours.  Most arrive by plane, although a few ski in or take 'alternative' transportation (fancy trucks, cars, bikes etc).  I enjoy watching the planes come in, and then the tourists shuffling over to the pole.  It's also fun when walking back from the telescope, because some times, I'll be watching the tourists watching me.   

Also, I enjoy watching the LC-130s land.  During December, we only had something like 3 flights for the entire month, so it was pretty special when they came.  But lately there have been multiple flights every day as the station gears up for winter, so they have become more routine.  On a clear day you can see the plane fairly far away.  Once it lands and drives down the runaway there is an enormous roar that fills the area.

Me, watching the tourists, watching me.  They generally aren't allowed to come into the station unless invited (although they often get an official station tour).  That little black building in the middle is an outhouse that is put by where they park their planes.

 Watching an NSF plane (LC130 Hercules) land,  when they come.

The station has two lounge areas where people can hang out, play some pool, watch movies, or grab a book from the library. 

The B2 lounge library.  This is the one I usually go to, as I'm often looking for a less intellectual book for my down time. The non-fiction library is downstairs.

One of the best places to relax is in the greenhouse.  The past two times I've been down here, the greenhouse was empty because it was being cleaned.  This year is completely different.  When you walk it, you are surrounded by a cloud of humidity and the smell of plants.  There is a small couch where you can sit and read, or even nap.

The sitting room in the green house.

The main portion of the greenhouse.

Beyond regularly scheduled activities, there are special activities, like the open house that SPT hosts every year.   We have chocolate and cheese, give people tours of the telescope, and then have a dance party.  It is quite the event.

The chocolate bar at the SPT open house!

 

The dance floor for the SPT open house (i.e., converted loading dock area with twinkly lights)!

At the end of December the second overland traverse arrived with more fuel for the station.  They hosted and open house, and as part of it, I got to drive one of the tractors.  I have to say, those are really nice machines.  At it's maximum speed of 7 mph, it was super smooth.

The tractor from SPOT 2 that I got to drive!

Here We Go!

It's been nearly a month since I last posted and SPT-3G has made a huge amount of progress in that time.  It's hard to describe all the effort and emotion that has been a part of this past month, but I'll try.   Working on an experiment at the South Pole is an all-out exhausting but exhilarating roller-coaster experience.  Every day is a new and different challenge.  The time we have is short since the last flight out leaves on Feb 15, and everyone has to be on it except our two winterovers.  SPT-3G a big complicated receiver, and not the kind of thing that we can just leave in pieces for them to finish up.

Around 10pm on New Year's Eve, we ended our first operation run of the receiver  and started warming up the cryostat.   A few days later, a new crew of SPT people arrived with the new detector modules.  From that moment on, it was a race against the clock to assemble all 10 wafers and install them into the focal.  It took about 3 days to complete the detector wafer assembly and about 2-3 more to fully assemble the focal plane and finalized the receiver.

The detectors are connected to cables using tiny aluminum wire bonds (they look like hairs and you usually need a microscope to see them).  The first step in assembling the wafers was to electrically check all of these connections.  Luckily, we have an automated setup to make these measurements for us (it's ~6400 measurements per wafer).  Based on these measurements, we go in and remove wire bonds that have become problematic.  The detector wafers traveled all the South Pole in specialized carrying cases, but they still feel all the vibrations and jolts of travel.  This is probably my least favorite step of wafer assembly because you have to have the detectors fully exposed.  But it does allow you to take pictures of the detectors themselves, which you can see below. Each of the little dark spots on the purple background are the individual antennas that bring the light to the detectors.  There are six superconducting detectors that are fed off each antenna, but they are too small to see in this picture.  For scale, the wafer is about 4.5" across.    Once plucking the wire bonds is done, we put the protective back plates back on and start connecting each of the 48 cables on a wafer to the readout electronics.  It's a slow process, but we (Adam, a postdoc from Fermilab and I) took our time and managed to do all 10 wafers with no mistakes.

An exposed SPT-3G detector wafer waiting for plucking of wire bonds.

The number of SPT-3G detector wafers grows!  Under the static bag in the back is a fully assembled module, and its counterparts are prepped and waiting for readout electronics.

More modules, fully assembled now.  You can see the electronics towers and the wiring coming off the top.

Next the wafers get installed into their spots in the millikelvin plate.  It was the first time we had all 10 spots filled and I have to say, it was a beautiful sight. Once the wafers are secured, we spent a couple days dealing with all the readout wiring on the other side.  Each wire has go to the different cryogenic temperature stages in order, or else the instrument won't get cold (and there are three stages).  Weaving the wiring in and around the different parts of the focal plane took about 20 straight hours in the end.  To keep wiring from touching different places we use dental floss (waxed, unflavored).  Sounds weird, but works great because it is strong but has low thermal conductivity.  You can see the result in the picture below where the focal plane is installed in the back of the cryostat.  The lenslets are pointing down the optics tube, and aren't visible in this picture.  Instead, you see the full glory of all the readout electronics.   And then we closed up the back of the cryostat, and that was it.  The SPT-3G receiver was fully assembled for the first time ever, and the last time unless we decide to open it during the next South Pole season.

The lenslet-side view of the focal plane as it sits on a benchtop.  10 modules!!!!

Myself, Chrystian, and Junjia with the fully assembled focal plane.  Chrystian and Junjia are two of the material science fabrication experts that actually made the detector wafers we installed.

Backside view of the focal plane, installed into the cryostat.  Lots of detectors results in lots of electronics and lots of wiring to deal with.

The receiver close-up team, in front of the fully assembled cryostat.  Left to Right: Jason, Zhaodi, Donna, Wendy, Me, Brad, Adam, Daniel.  

Closing up happened around January 10, and then we were in a holding pattern waiting for the receiver to cool down.  It takes about 7 days total to bring the receiver down to 4 degrees Kelvin and then the detectors to 250 millikelvin.  During that time, we got in a little bit of leisure time and rest (another blog post coming soon on this) and prepped plans for operating the receiver.   The receiver got cold right on schedule and we started working on setting up and operating the detectors.  We've never operated this many simulataneously before, so there were some kinks to work out.  There still are some, as we're learning more about our new detectors and electronics, but we've made some steady progress.   A little less than a week later it was time to hoist the receiver into the telescope.  We did a test lift back into December, so we had a general idea of what we were going to do.  But lifting a 2500 pound cryostat up many feet into the air through a space with only a few inches of clearance on side without damaging it is still a big operation.  The lifting itself went truly smoothly.  Attaching the receiver to its mount in the cabin was very challenging because it requires an extremely precise alignment of the cryostat.  But in the end we got it.  In case you are wondering how we hold such a big instrument into the telescope, the answer is some really big bolts.  There are four of them that connect mounting points on one side, and then two stiffener bars that come on the other side.  In the picture below, I'm holding one of the main bolts that holds the cryostat into the cabin. 

Preparing for the lift of the cryostat into the telescope cabin!.  That's an M20 bolt, one of four main bolts that hold SPT-3G in place.

And it's up!  The SPT-3G receiver fully lifted into the telescope cabin.

 

After the cryostat was lifted, the next day we lifted our electronics up and worked on hooking everything up.  That was last Friday.  Since that time we've been working towards operating the detectors and telescope as we push towards first light (but that's another very special post).  

In the meantime, the summer season at the South Pole is starting to wrap up.  I realized I haven't posted a lot of pictures of South Pole itself, and we had some really beautiful lighting the other day.  So here it is, one of the entrances to the Amundsen Scott South Pole station.  This is one of the first things you see when you get off the plane, and its the door I use every day going back and forth to the telescope.   If you look carefully, you'll notice the station is actually elevated above the snow.  Snow drifts are a huge problem and buildings are continually getting buried over time (including SPT and the dark sector lab building it is attached to).  The design of the elevated station helps it resist this build up by directing the wind.  The whole station can also be jacked up higher when needed to increase the lifetime of the building.

South Pole Station.

I also spent some time working on the roof of SPT the other day and took a nice panorama showing the view out to the horizon.   I really love looking out at the great nothingness there, but it does get cold fast when you are on the windy side of the telescope.  I also took a panorama from the room of the building attached to SPT (the dark sector lab).  You can see the MAPO building (home to the Keck array CMB telecscope), elevated station, and Ice Cube lab in the distance.

View of the South Pole area as seen from the room of the dark sector lab.

Horizon view from the roof of SPT.

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.