Closing Black Cat

Well, it’s been a busy week.  The receiver cryostat for our camera arrived a bit late, only last Saturday afternoon, and we’ve all been working hard to install the focal plane and get it cooling for the first (nearly) fully populated SPTpol focal plane tests.  Very exciting!

The SPTpol receiver cryostat is almost identical to the cryostat used for the SPT-SZ camera, (the camera that’s been on the telescope since 2007).  The biggest visual difference is the color.  The old cryostat is red, while the new one is black.  While building it up and testing it at Chicago, Brad and Abby named it “Black Cat,” or “El Gato Negro” as the sticker on it shows.

The Receiver team and Black Cat.  From left: Liz, Brad, myself, and Abby.

Let me do my best to walk you through the close up.  We started by finishing preparations on the focal plane.  Along with the receiver came little shims for the 150 GHz modules.  Each has a slightly different height because the silicon wafers in them are all slightly different heights. To make sure everything stays in focus, we shim up the shorter modules to match the height of the tallest module.  This meant removing all the modules and re-installing them, but this time plugging in all of the readout boards.  Next we installed the filters that go in front of all the feedhorns.  These filters define what color of light the detectors are looking at.  Without the filters the detectors would see too much light and they’d fail to operate correctly.  Finally, radio frequency (RF) light is bad news bears for our system, so we close up the gaps between temperature stages at the front of our camera with annuli of aluminized mylar, which makes an electrically conducting seal that blocks radio light from getting in, much like the metal mesh in the door of your microwave keeps microwave light cooking your food and not your face.

We shimmed the modules to be the same height, and taped over holes in the focal plane where more 90 GHz pixels will be installed in a couple weeks.

All 18 readout boards installed on the back of the focal plane.  They are attached to the detectors with flexible circuit striplines.

Filters are placed in front of the horns to block out light we don’t want the detectors to see.

RF light can ruin our readout, so we put aluminized mylar between the different temperature layers.

John Carlstrom, the project PI, flew home before we could install the camera, but he left a note for us.

With the camera built up and ready to go, we started installing it in the cryostat, which was a multiple day process.  It’s not just a matter of screwing the camera into the cryostat and calling it a day.  We also have to connect thermometry to the camera so we know how cold it is, and we have to heat sink each thermal stage of the focal plane to our millikelvin fridge so it actually gets colder.  The fridge does the cooling, and we attach the camera to the fridge by three flexible copper heat straps, each at successively warmer temperatures so we don’t blow the detectors out of the water with too much thermal power.

Abby installing the camera in Black Cat.

Liz and I installed RF boxes for readout cards while Abby attached heat sinking straps to the focal plane.

We also have to heat sink all of the readout wiring coming out of the back side of the receiver.  Each cable gets sunk to multiple temperature stages, each a little warmer than the last as the cable winds its way back out of the cryostat and into the room temperature world.  Heat sinking is REALLY tricky.  There are 18 cables coming out of the camera.  One end of the cable is in contact with the 250 mK cold stage.  The other end is at room temperature (300 K).  You have to clamp the cables down at incrementally hotter temperatures so the coldest stage stays cold.  Well, you can imagine with 18 cables in close proximity it’d be pretty easy for two lengths of cable at different temperatures to accidentally touch and warm up our detectors.  Whoops…  So Abby, Liz, and I spent a lot of time designing and planning how to attach the cables to the various temperature stages, and then actually doing it to so there were no thermal touches.

Heat sinking bars attached to the back of the focal plane.  Liz had the awesome idea of adding bars to the pre-existing heat sinking ring so we can bring the cables out radially.  Abby and I designed the parts, and Liz’s advisor Bill machined the new parts for us.

Liz tying a copper heat strap up with dental floss to keep it from touching another heat strap.

Once all the readout cables were attached we could actually close Black Cat.  The first radiation shield (at 4K) is split into two parts.  We put the first part on and taped all of the readout cabling to its under surface.  This keeps the part of the cables at 4K from touching the cooler part of the cables less than an inch below them.  From there it’s pretty simple: put the other half of the 4K radiation shield on, cover it in aluminized mylar super-insulation, put the 50 K radiation shield on and cover it in super-insulation, and put the 300 K radiation shield on, which has the vacuum seal.

All of the readout cables attached and sunk to the various temperature stages.  The thin orange cables get taped up to the cryostat ceiling.

4 K and 50 K radiation shields on, and super-insulation installed.

Closing up the external 300 K shield.

At this point Black Cat was only partially closed up.  When we flipped the cryostat over the other side needed some work too.  This is the side that has a window that gathers light from the telescope.  Liz and Brad had already installed some baffling in the window that Abby and I had previously covered in black goop that absorbs stray light.  You can get some nasty reflections in the telescope’s optics chain, and you want to get rid of light that doesn’t actually hit the detectors straight away.  Light that doesn’t can bounce around and enter the detectors at a later time and confuse us by looking like it came from a different part of the sky than it actually came from.  So we add baffling to control the path of light and stray reflections, and blacken the surfaces in the light’s path to the camera so that stray light gets absorbed.  After the baffling we add a lens to focus the light on the focal plane.

A view of the focal plane installed underneath the extra light baffling.  We’re looking through Black Cat’s window after the cryostat was flipped over.

Brad and Liz installing the lens.

Just like the camera, Black Cat’s window needed some filters and RF shielding, so we installed those next.  The RF shielding mylar is really thin and fragile, so installing it is a tricky business.  There are lots of screws that hold it in place and one slip of the screwdriver means popping a hole in the mylar and starting over.

Installing a 50 K filter into the system in front of the lens.

Installing more RF shielding.

RF shielding installed!

The receiver cryostat is one of two cryostats in the system.  The secondary mirror of the telescope is also in a cryostat, called the Optics cryostat.  This thing is enormous (about the size of a VW beetle).  It accepts light from the main dish of the telescope through one window, then focuses it into the receiver cryostat and onto the camera through another opening.  All of this stays under vacuum and stays really cold, so that means we have to mate the Optics cryostat with the receiver cryostat to effectively make one giant cryostat.  To do that, we needed to install mating cones on Black Cat.  There is a cone for each radiation shield layer: an outer cone at 300 K that also holds vacuum, a slightly smaller nested cone at 50 K, and a still smaller cone at 4 K.  With the cones installed, we put one more filter in Black Cat designed to keep hot light from warming up the filters underneath it, and then we were ready to mate the two cryostats.

Installing the mating cones so we can attach Black Cat to the Optics cryostat.

Mating the cryostats is a bit tricky.  There are two quarter-inch dowel pins in the opening of the Optics cryostat and if the two cryostats don’t line up perfectly when you push them together you can bend the dowel pins and get them permanently stuck together.  More bad news bears.  So, to control the mating process both cryostats are on chain hoists.  It takes several people to hoist the corners of the cryostats just so to get them perfectly level, then a couple more people to slowly push the cryostats together and seal them up.   Once the screws were tight and the cryostats were detached from the chain hoists, we moved them into position for testing and started pumping down to get them under vacuum.  Five days from now we should be cold enough to start taking data.  That’s the plan, anyway.

Preparing to mate Black Cat to the huge Optics cryostat.

Tightening screws after Black Cat was mated to Optics.

To celebrate the close up and to relax a bit, we all spent some time in the station sauna, then ran out to the Pole in our bathing suits for a picture.  It’s really not as bad as it sounds.  You’re sweating like crazy in the sauna, which is sitting around 200 degrees, so you can stay outside for several minutes before getting really cold.  And yesterday was pretty warm – only -35 F or so with wind chill.  We went to the Pole once, but cycled between the sauna and the station entrance outside several times to prolong our sauna session.  On the last cycle, Brad, myself, and a grad student from McGill named Tijmen decided to have a little competition to see who could stay outside in our bathing suits the longest.  (It was actually my idea and they were willing to go with it).  Brad is from Wisconsin and I’m from Michigan, so we were doing just fine, but Tijmen (who is from the Netherlands) was shivering like crazy.  The man has some determination, though.  After some awesome intimidating stares and several minutes of standing out in the cold as our body hair frosted over, Brad finally gave in to warm up his fingers.  I stayed out an extra minute or so but Tijmen and I were both starting to get pretty cold, especially our fingers and toes, so we decided to go back inside as joint winners.  Well played, sir!

Me in my bathing suit standing at the geographic South Pole after a session in the sauna.  Black Cat is closed!

Christmas is this weekend, and that means the Race Around the World and Christmas dinner, so stay tuned for another update soon.

Good luck, Black Cat!

100 Years After Amundsen

     December 14th marked the 100^th anniversary of Roald Amundsen and his ski team reaching the South Pole, the first time in history anyone had ever set foot on the geographic South Pole.  Amundsen was Norwegian, and at the time Norway had been a country for only a few years, so this achievement was important for the young country.  To celebrate this historic event, the South Pole Station (Amundsen-Scott Station) was visited for the last several days by the Prime Minister of Norway.  It’s a little exciting to have a head of state roaming around, and it’s definitely been a bit different around the station. (Scott arrived a few weeks later, but he and his team didn’t make it back…)

     You’d think with a head of state visiting that there would be dozens of support personnel and security (they’re certainly would be if President Obama visited, I’m sure).  Well, Prime Minister Jens Stoltenberg does have some support staff, but security is really nowhere to be found.  It’s quite remarkable and refreshing to see someone in the position that Prime Minister Stoltenberg is in be so down to Earth and relatively approachable.

     He arrived with a crew of Norwegians on Monday, and spoke a bit at dinner that evening thanking the station and the US/NSF for our hospitality and for the chance to be here to celebrate such an important event in Norway’s history.  An hour or so later the whole station went out to the geographic Pole for a group photo.  (At least, we went out to where it was last year on January 1st.  It moves about 30 feet every year due to the ice/glaciers moving and pulling the station and everything on the surface with it).

The Prime Minister of Norway addressing us at dinner on Monday.

     On Tuesday the Prime Minister toured the various lab facilities in the area (by skiing to each location, of course).  He made a stop at DSL and Brad gave him a tour and an overview about the science we’re doing.  It was pretty cool for the Prime Minister to see all the work we’ve been doing for so many years.

     Wednesday was the actual centenary of the Amundsen’s arrival, and at 4:00 PM all of us gathered around the ceremonial Pole to hear Prime Minister Stoltenberg give a speech and watch him unveil an ice bust of Amundsen.  There was another ceremony at 4:00 AM, apparently marking the moment in time when Amundsen wrote in his journal that his team had made it to the Pole, but I skipped that one.  There was a live TV feed to Norway, though, so I imagine it was mostly in Norwegian while the speech earlier in the day was all English.

The PM unveiling an ice bust of Amundsen on Wednesday.

     The station wasn’t only visited this week by the Prime Minister and his staff.  A whole slew of people skied in to stay at the NGO (Non-Governmental Organization) camp a kilometer or so from the station.  All told, there were 93 people in the camp, which was comprised of dozens and dozens of tents.  Some of these people skied the last degree of latitude (89 to 90 South), and a couple people even skied all the way in from the coast, taking the same path that Amundsen took.  A bunch of us went out to take a peak at the NGO camp late Wednesday evening, and these last two heroic skiers were only just arriving, around 11:30 PM after weeks of traveling.  The weather was starting to get a little worse around this time too.  Fog was rolling in and when we were at the NGO camp we couldn’t see the station at all.  Thankfully, there are flags every 10 meters or so to help you along the paths…

The NGO camp. Sleeping in tents seems crazy to me, but there are 93 people out there!

Fog was starting to roll in, enough that the station wasn't visible from the NGO camp.

The start of a frost beard after my trip to the NGO camp.  Some people grow some seriously awesome frost going back and forth to the telescope.

     After these last two skiers departed to drop off their gear and head into the station for a meal, I decided to take some close up pictures of the Amundsen ice bust and the ceremonial Pole now that there was no longer a crowd.  I also wanted a better look at the geographic Pole since I didn’t get to linger when the group photo was taken the day before.  As I approached the Pole a group of Norwegians were walking back to the NGO camp, but one lone Norwegian was standing around by the Pole.  (In case you’re wondering the Norwegians have different gear than us so they stick out pretty easily).  Anyway, this guy at the Pole appeared to be talking on what I thought was a radio, so I approached from behind so as not to interfere, taking a picture of the sign marking the location of the Pole.  I then headed around the sign to take a picture of the marker on the Pole (it’s different every year), and ‘lo and behold, the sole Norwegian was the Prime Minister on a satellite phone, not a radio.  I nodded at him, took a quick picture of the marker, and headed back in.  It was sort of a surreal moment.  I mean, would you expect the head of state of a country to just be hanging around by himself like that?  It was really refreshing.

A close-up of the Amundsen bust, with the Sun behind it. The station is directly behind me. Did I mention this picture was taken right around midnight?

My reflection in the ceremonial Pole. Flags of the countries that signed the Antarctic Treaty are in the background and in the left of the reflection. In the right of the reflection is the station.

Another shot of the ceremonial Pole with the station in front of me.

The sign marking the geographic South Pole (it's location on January 1, 2011).

The Pole marker this year was a compass. The guy in the background is the Norwegian Prime Minister.

     On Thursday morning, the Prime Minister was scheduled to depart from the Pole, along with many other people, a couple of whom were part of the SPT team (John Carlstrom, the PI and my undergraduate advisor, and Keith Vanderlinde, a post-doc at McGill who was a winterover for the project several years ago.  He also took some amazing photos of the night sky during his winter, including the background picture on my blog).  The weather was horrendous – we still couldn’t see very far, and the telescope was completely obscured from the station – and that would normally mean the flight was canceled.  But, having an important official on a flight means things happen that wouldn’t normally, and their plane took off more or less on schedule.  And that was that.  Back to our regularly scheduled programming.

Two SPTers and the Prime Minister, along with several other people head out to a Herc for their flight back to McMurdo.

The South Pole

     It’s been a few days since I last posted, but I’ve been at the South Pole for about 48 hours now (as of writing this – I have to wait for the satellite to come back up tomorrow morning to post).  So much has happened already, and with the sun up 24 hours a day I’m already having troubles keeping events from the two days apart, but I’ll do my best to fill you all in on the good stuff.

     Before I get to what it’s like at the South Pole, I should post a few more pictures from McMurdo.  The day I landed it was overcast so I didn’t get a chance to really see the surrounding view.  Well, transport to the airplane for my trip to the Pole the following day wasn’t scheduled until 2:30 PM, and it was a beautiful clear day, so some of us walked back out to Discovery Hut to take in the view.

The view from Discovery Hut on a clear day. Much better!

Liz taking pictures of the view.

     After the hike, we returned for lunch, then packed up and headed out to the airfield.  There are several airfields at McMurdo, and we flew in and took off from the Pegasus Airfield, about an hour bus ride from the station (but it’s maybe only 10 or so miles from the station).  When we got back out to Pegasus we had to wait for the aircraft (a C-130 Hercules) to fuel up and pack cargo, so we had an hour or so to kill in the airfield galley.  It was really sunny and warm, so we went outside and took pictures of the view.  Mount Erebus, a volcano that formed Ross Island, was visible from the airfield, smoking slightly.  We even had a snowball fight.

Me in front of Mt. Erebus in the background.

     Finally it was time to board the plane and take off, the last leg of a long journey.  This flight was relatively short, just over 3 hours, and we landed around 10:00 PM, Tuesday Dec 6.  When we landed we were greeted (following tradition) by colleagues already at the Pole.  They gave us a warm welcome of handshakes and hugs and carried our bags into the station for us.  The barometric pressure at the time resulted in a physiological altitude of 10,700 feet, so we were all a little winded coming up the two flights of stairs to reach the first floor of the station after coming off of several days at sea level.

On the C-130 Herc.

     So, what it’s like at the South Pole?  It’s totally featureless minus the station, it’s cold, and when the sun is shining it’s really bright.  The temperature has been pretty mild so far, though.  Both days have been between -20 and -15 F, with windchills between -30 and -35.  With all the gear they give you, it’s really not bad at all.  I’ve certainly experienced worse growing up in northern Michigan, but then I didn’t have to walk kilometers in that.  As you’ll see in a little bit, the telescope is about a kilometer from the station and we generally walk that back and forth two or three times a day.  While I’ve been using the Carheartts and red parka (affectionately known as Big Red), gloves, neck gaiter and sunglasses/goggles, it’s been warm enough for me to wear a nice pair of socks and my usual everyday shoes back and forth instead of my big boots.

     24 hour sunlight is definitely a little strange, but thankfully it hasn’t disrupted my sleep too much.  It’s kind of nice because the station is built so that one side points towards the sun when it’s roughly noon in New Zealand.  Since we keep New Zealand time here, it gives a nice way of telling time if you’re outside for any length of time (which hasn’t been the case yet, thankfully).

     I was lucky and got a room in the station.  Most of the time scientists get rooms in the station, but when the population gets high in the middle of the summer season, sometimes you’re put out in “Summer Camp.”  (The population is currently 239, and pretty much peaks at 300.  In the winter the population is about 60).  Summer Camp is a bunch of half-barrel shaped buildings a hundred yards from the station or so where people get to rough it a bit more.  Have to go outside to use the restroom and use extra pairs of thermal underwear to plug drafty holes in the wall.  But besides the limit of showers (two two-minute showers a week), there’s just no way you can call living in the station roughing it…

The Amundson-Scott South Pole station. Next week marks the 100th anniversary of Amundson reaching the Pole. Scott reached here a few weeks later.

Summer Camp. Glad I don't have to sleep out there.

Instead, I get to sleep here!

    The station has just about everything.  It’s got a full court gym, weight room, music room (complete with a theramin), arts and craft room, game room with a pool table, darts, foosball table and what appears to be several hundred books, a sauna, two or three rooms with relatively big televisions for watching movies, a greenhouse, a station store, and a post office.  Oh, and I forgot to mention several conference rooms, a computer lab, and a science from which we can monitor our experiments remotely.  We even have internet, at least when the satellites are up.  It’s incredible the infrastructure that exists mere feet from the actual South Pole.

     This post is getting really long, so let me end with a few pictures of the South Pole Telescope (known as the 10-meter down here since there are several telescopes and observatories).  The first picture below is the view of the 10-meter (the big white structure) attached to the blue lab we all work in, the Dark Sector Laboratory, or DSL.  (The land around the station is separated into several sectors, all used for different types of experiments.  The Dark Sector is kept, well, dark.  No extra lights (not that you need them in the summer anyway) or extraneous radio communications that could interfere with the observations of the telescopes out there).  As you approach the 10-meter it really hits you how enormous it is.  Besides the station, it’s the largest structure at the South Pole.

The view of the 10-meter at DSL as you get close.

SPT close up. This thing is just plain huge.

The back side of the telescope.

     We’ve already done a ton of work, but I’ll leave that for another post.  I do want to give a sneak peak, though… here is a picture of me holding up the partially assembled camera.  All seven modules I worked on are installed in the center, and most of the other pixels are also installed, (currently taped off).  I’m a little biased, but this thing is gorgeous!

The back side of the camera, (partially assembled).

Me holding the partially assembled camera up. I've been working on the seven gold modules in the center for the last couple years.

Mactown

     The ice flight to McMurdo was a success!  No boomerang for us.  We also learned why the call time for our flight was so ungodly early.  Turned out there were a bunch of penguins on there way back to Sea World in the States and the C-17 cargo plane we took down to Antarctica needed enough time to get back to Christchurch with them on the same day.

     We got picked up from our hotel at 2:00 AM and headed back to the CDC to get into our ECW gear and check our luggage for the flight.  Here's a picture of me in my Carhartt overalls with all of my bags and ECW gear before the flight.  I got a bit of sun during my stay in Christchurch.

Me before boarding the plane.

Like I mentioned earlier, we were taken down in a C-17 cargo plane.  The number of passengers depends on how much cargo they ship down.  We only had about 50 people this morning - the rest of the plane was filled with cargo, everything from a giant refrigerator unit to pallets of coke and Coors Light.  There were a few seats at the front that were just like a commercial airliner, but most of us sat on canvas seats on the walls of the plane.

I was on a flight taking Coors Light and Coke of all things to McMurdo and the South Pole.

Most of us sat on the walls of the aircraft.

     The flight to McMurdo from Christchurch takes a bit over five hours, and we took off around 4:30 AM. I slept quite a bit on the flight, but I woke up just in time to look out the window and see the edge of the line of ice and icebergs marking our rapid approach to the continent.

The view out the roughly 6 inch diameter window on the C-17. Starting to see some ice...

  We landed about an hour later and made our way to Ivan the "Terrabus," a big school bus-like vehicle with treads that took us from the Pegasus airway (one of several landing strips at McMurdo - also the furthest from the station) to the station proper.  McMurdo Station is known as "Mactown" around here.

Disembarking from the C-17. Antarctica in the background! We landed on the frozen ocean, and McMurdo is built on Ross Island, so I haven't technically set foot on the continent yet.

     After sitting through a Station orientation, grabbing linens to make our beds, and sorting some luggage, we decided to take a quick hike out to Scott Hut.  It's an old wooden hut made back in 1902 during the Scott Antarctic expedition.  The hut is in remarkably good shape.  It looked to me like it was made only a few years ago.  I guess it's sort of perserved by the dryness and temperature.  Hanging out near Scott Hut on the ice were a bunch of seals.  Sadly, I haven't spotted any penguins yet.

A cliff on our hike overlooking the ocean. I hear the view is spectacular on a sunny day. Maybe on my return trip...

Scott (Discovery) Hut, made during the 1901-1904 Antarctic Discovery Expedition

Seals hanging out on the ice.

     It's almost dinner time, and after that we have bag drop (we check in our bags for the flight south to the Pole tomorrow morning), so I'm going to finish up here.  I'll leave with a picture of me standing near Scott Hut with Mactown in the background.

Me and Mactown.