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.

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.

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.

In Transit

It's a big year for the South Pole Telescope.  We are installing a brand new camera, that has 10 times as many detectors as the current camera.   This means that everything except the main dish of the telescope it getting overhauled.  New optics, new cryostat, new detectors, and new readout electronics.  It's a huge job, but we've also got a great team (myself included) going down to take care of it.   I'll talk more about SPT-3G in future posts.  For now, here are some pictures of the new receiver that I took before it left the US.

This is the SPT-3G receiver during our final testing before shipping.  The big cylindrical tube holds the optics used to focus the light onto the camera.  The camera itself sits in the box shaped structure.  To give a sense of scale, the whole thing end-to-end is about 9 ft long.

This is the receiver from a different angle.  The white circle at the end is the window where millimeter-wavelength light will enter.

The first group of SPT people that I'm traveling left the states last Sunday.  In theory we were supposed to have 1.5 days in Christchurch, 1 day in McMurdo, and then arrive at pole on Friday.  Unfortunately, the weather in McMurdo didn't hold, and our ice flight was cancelled.  A few of us took the opportunity for some hiking in the hills in between Christchurch and the neighboring town of Lyttleton.  The trail was short and steep and we ended up with some fantastic views along the way.

The view from nearly the top of the hills.  Our hike started down at the port town you can see in the middle of the picture.

We did manage to make it to McMurdo the next day, and brought a very special visitor with us on the plane.  Secretary of State John Kerry came to visit Antarctica for two days to see the impact of global warming.  He gave a special meet and greet for McMurdo residents, speaking about his experiences  fighting for the protection of the environment.  He is an extremely dynamic speaker, and it ended up being a fantastic experience and a real emotional lift. 

The inside of the C17 aircraft from Christchurch to McMurdo.  The plane had fewer people than I've traveled with in the past, but was stuffed full of cargo.  The big box in the lower right contains part of the SPT-3G cryostat!

Above are a couple of pictures showing our first view of Antarctica from the window of the plane.  You can see some mountain ranges on the left and the actual coast of the continent.  The picture on the right shows some of giant ice flows in the ocean.  It's my third trip to Antarctica, but I was still really excited to get that first glimpse of ice.   Our flight to pole is now rescheduled for Monday morning, so we're taking the time to experience McMurdo while we wait.  It's a balmy temperature of 18 F (-8 C) outside, so really beautiful weather to enjoy before getting to pole.