Thursday, 29 December 2016

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!

Tuesday, 20 December 2016

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.


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.

Tuesday, 6 December 2016

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.

Thursday, 24 November 2016

The Heart of SPT-3G

We have finished packing up the old SPTpol camera and are now working on assembling all the components for the SPT-3G camera.  My first job was to connect readout electronics to our detector wafers.  I'll talk more about how our detectors actually work in another post, but for now, they are basically extremely sensitive thermometers that measure the heat of incoming light. Each detector wafer is custom fabricated at Argonne National Lab and has 1600 superconducting detectors, making each one as sensitive as the entire SPTpol instrument.  We will have 10 wafers in the full camera, but for right now I'm prepping two for an initial commissioning.

We ship the detector wafers pre-packaged down to the pole.  Each one has an array of lenslets that will couple the incoming light from the telescope into the detectors, and then a protective holder.  You can't actually see the detectors when they are in this package, only the lenslets and back cover.  There are, however, gaps in the back cover that allow cables to come out of the package.  Conversely, these holes also allow things to fall onto the detectors, so doing the readout assembly is a job that requires a lot of concentration to prevent mishaps.  The picture below shows the work bench in our clean tent.  The hexagonal object in the white cylinder is the detector wafer (the white lenslets are visible).  Fun fact, just like on a pair of glasses, we anti-reflection coat our all of our optics, including the lenslets.  The white layer you see is actually that coating, tuned to millimeter wavelength light.  The other main object in the picture (green circuit boards with honey-colored wiring coming off) is the first set of readout electronics to be assembled.

The first SPT-3G detector wafer to have readout assembled onto it at pole!
The readout electronics go on the back cover of the detector assembly, where all the cables are.  So I have to flip the detector assembly over, and pull all of the cables out of the way.   It looks a little silly when it's prepped, but it's important to manage all the cables so that they don't get damaged.

The same SPT-3G detector wafer with all the cables ready to be hooked up.

Now the wafer is ready for me to plug in the readout boards one by one, and then screw them into the back cover.  Here's a picture of the first one in place.  Again, it looks silly because I've covered everything with sticky notes, but it's a great way to prevent any screws I might drop from falling through a hole and damaging the detectors.

One board in place, 11 to go!

Then I just work my way around the back cover until all the boards are connected and in place (12 total).  Both SPT-3G wafers are now fully assembled and once we've built up the receiver, they'll go straight into the middle section of the new camera. 

Both SPT-3G wafers, ready to go.

Top down view of one wafer assembly.
Maybe I'm just a little biased, but I think the finished products are awfully pretty.

Saturday, 19 November 2016

Goodnight SPTpol

Our group finally made it to the South Pole late Tuesday night.  And through some good luck, the group of SPTers following us made it through on Thursday.  The plane flight was stunning as always.  I didn't get a lot of great pictures this time, because the windows on the LC130 (Hercules or Herc for short) were pretty scratched.  But here is one I do like of the Transantarctic mountains as we flew over.  The plane flies at an altitude of about 20,000 feet, and some of the mountains look enormous, so they have very high peak elevations.  I like this picture because I see the illusion of movement in the glacier below.

One view from the plane flight to the South Pole.

Now that we are here, it's time to get to work.  Our first job has been to decommission the old SPTpol receiver.  SPTpol was a great instrument that has collected five years of data now and we have some really fantastic measurements of the Cosmic Microwave Background with it.  We had our winterovers turn off the mechanical coolers that maintain the ultra-cold interior of the cryostat and then proceeded to start removing all the cables and electronics.  SPTpol has now been taken out of the receiver cabin, and is sitting inside the telescope building for us to box up for shipment back to the US.  We'll keep some of the electronics here at pole as spares, but for the most part, everything goes.  Our crates containing SPT-3G have started to arrive at pole, so soon we'll start bringing in all the new stuff.

The SPTpol receiver.  The big white cryostat on the left contains the SPTpol mirror, and the black one on the right contains all the SPTpol detectors.

The empty receiver cabin where SPTpol used to live (and where SPT-3G will get installed).  You can see the light coming in at the very top of the cabin, where the cryostats look when they are installed to see the primary mirror of the telescope.  This entire room moves around with the telescope as it scans the sky.

The SPTpol optics cryostat leaving the building.  It's a big piece of equipment that we don't have space for with all the new stuff coming in.  It's so big it can't go out the normal doors, so a snow ramp was built up to some removable panels in the side of the building.  The cryostat was taken to another location away from the telescope where the South Pole carpenters can build a crate around it for transport back to Chicago. 
New SPT-3G cargo entering the building through the same panels.    
The SPTpol packing/SPT-3G unpacking crew.  We're standing in front of the new SPT-3G cryostat.  You can't see it very well here, but there will be many more pictures to come as we continue assembly.

Sunday, 13 November 2016

Running in Place

We're now in day 4 at McMurdo and it feels like we are running in place.  Friday, we had some hope that we would get scheduled for the Saturday morning flight to pole.  Sadly, that flight never made it out and we ended up spending the weekend since there are no flights on Sundays.  Luckily for us, we know some of the other scientists working at McMurdo and got to see their experiments to pass the time.  

First we got to tour around with an old friend of Brad's from Berkeley.  Yuki is a summer science technician at McMurdo and is responsible for maintaining a variety of experiments.  First up was CosRay,  a physics experiment to measure cosmic ray showers.  Cosmic ray showers occur when energetic particles (like a proton or electron) collides with the atoms and molecules in the earth's atmosphere.  The collision creates new particles and then those particles collide with atoms and molecules and the process repeats. This creates a shower of particles in the atmosphere and can be detected on the ground.  By measuring the air showers, CosRay learns about the sun and anything else that produces cosmic rays (like supernova).  CosRay is the longest running experiment at McMurdo and is finally shutting down later this summer.  I didn't get any good pictures of CosRay, because it just looks like giant boxes of styrofoam (thermal insulation protecting the detectors).  But I did take a picture of their old bit bucket.   CosRay used to use punch cards for recording the airshowers measured.  The bucket below is filled with all of the old 'bits' that got punched out before they retired it.
The CosRay bit bucket.

 Up next was a quick look up observation hill for Yuki to check on a GPS unit.  While there, we stopped and saw the marker that shows the old site of the nuclear power plant for McMurdo. Yes, that's right, nuclear power plant.  It was fully removed in the 1970's after it went critical in 1962.  It's a sad reminder that we weren't always great conservationists and stewards of Antarctica.  In case you are wondering, these days McMurdo runs primarily off of diesel fuel and also some wind energy.

The nuclear power plant marker on the side of Obs Hill.  You can see most of McMurdo down below.
The inscription on the power plant marker.

There is also a beautiful view of Mount Erebus from Obs Hill.  That's an active volcano (see the tiny cloud at the top). 

Last stop on Yuki's rounds was arrival heights, to check on the variety of experiments up there (mostly atmospheric, some weather).   From the top, you can see Cape Evans where Robert Scott built a hut in 1910 during his Antarctic explorations, and the further out towards open/frozen ocean.  With all the ice in the bay right now, it is hard to imagine that in two months there will be a ship arriving to resupply McMurdo.

Cape Evans in the distance.

Saturday,  Jessica and I hopped on a shuttle to head out to the Long Duration Balloon (LDB) facility to visit her friends on the Anita experiment.  Anita is looking for cosmic neutrinos that  interact with the Antarctic ice and create radio emission.  Instead of looking up like the South Pole Telescope, Anita looks down at the ice as it flies over, listening for radio pulses.   Cosmic neutrinos are generated by some of the most energetic events in the universe (like supernovae). Neutrinos don't interact or get attenuated as they travel through the universe, so measuring them opens a whole new way of exploring these types of astrophysical events.

The top of the Anita gondola, suspended in one of the LDB high-bays for assembly.  Each of the horn-like boxes are a different receiver for Anita.
A view of Anita from the bottom.

Sunday afternoon, we went on down to the observation tube.  When conditions allow, there is a tube in the ice that has a tiny little room at the bottom with windows.  You climb down all the way through the ice and end up being able to see out into the water.   They put the lid back on the tube to help keep it dark and allow your eyes to adjust.  Everything down below is quiet (although you can still hear your friends talking on the surface). As you sit, and your eyes adjust, you can all of the ice crystal formations growing down into the water.  While I was down there, I was able to hear a seal pinging.  It sounded a bit like a very eerie low-pitched hooting with a little bit of wail to it.  And then the seal appeared, swam around some ice formations for a bit, and was gone again.   There was also an entire school of what I think were fish, but might have been some sort of strange Antarctic sea bug.   I could have spent the whole afternoon down there (it wasn't even cold).  The obs tube is probably one of the most memorable things I'll ever do in my travels.

The observation tube in the ice and its lid.

The view underneath the ice.  The picture doesn't come close to doing it justice.  You can see the land of Ross island on the left, and then the ice crystals growing down into the water.  The bright spot on the lower right is a fish!
Me, coming back out of the obs tube.

Today, we're in a bit of a holding pattern again as we wait for our flight to go through.  We were scheduled to be transported to the airfield at 0615 this morning, but the weather here was very cloudy with a bit snow flurries.  We almost got out later this morning, making a mad dash to transport when they moved it up on us, but that flight got cancelled as well. Now we're hoping to make it out this evening, but we heard from our winterovers that the visibility at pole is not good today.  But at least the view out the window here is beautiful to look at while sitting in the science lab.