Focal Plane Installed

We finally completed the installation of BICEP-3’s focal plane the day after Christmas.  The optics (two lenses) in our camera cast a magnified image of the sky onto this place, which we stuff full of detectors. 

Assembling this has been my main task (as well as three other peoples’) for the past couple weeks since I arrived.  There's a couple of us at work above.  Those nine boxes (or “modules”) each contain 64 pixels.  Because they are delicate and we did not want them to get held up in New Zealand customs, I had to “hand-carry” them down here, taking them as carry-on in a hard-case that looks like something out of a cold-war spy movie.  It's customary to give goofy nicknames to important hardware, and we're considering naming each of the nine modules after a Supreme Court justice (can you think of any other things that come in sets of nine?)

You’ll notice that there’s room for another 12 around the edge, and next year we’ll bring down another 11 (we don’t have enough wires in the camera to read out the last one).  For now, however, we will just have nine.  (I suppose when we add the others, we'll either have to change our nickname scheme or call it "packing the court").  The next immediate steps from here are to add lenses in front of the detectors and insulation around them so we can cool them to -450F.  We hope to be cooling down in the next couple days.

Those detectors need to be made even colder than the lenses, and we keep them cold by having successive “stages” at progressively lower stages, kind of like how one dresses in layers on a cold day to more easily stay at a different (albeit warmer) temperature.  You can see the final stages of that here

We call this structure "the wedding cake" (another goofy nickname) because of it's stacked multiple stages.  Here's a couple of us having some fun with that name during installation.

The installation wasn't all smooth sailing.  You can see the clips in the top picture that I had to improvise and machine last minute to hold the filters in place.  I also had to open one of the detector boxes and re-wire it to avoid some electrical cross-shorts.  You can see me threading the "wire-bonder" machine below that I used to make these fixes:

Penguin for Liam

Hey Liam, I found you a penguin.  He was outside of the coffee-house in McMurdo station and has come to the South Pole with me to help out. 

Here he is advising us on the fridge.  Since he's from a cold climate, he has natural expertise in cryogenics:

When we’re done here, I’ll bring him home to you.  What should we name him?  I’ll post photos of him from time-to-time.

Note to anyone from the US Antarctic Program eves-dropping on this: in case it isn’t obvious, this is a plush-toy, not a real penguin.

Note to everyone else: the US is one of many countries to have signed the Antarctic Treaty designed to preserve the pristine wilderness on the continent.  Signatories make no territorial claims and do not recognize others.  Military is kept off the continent except in support of scientific research missions.  And individuals are not supposed to export materials from the continent, alive or inanimate without permission from regulatory bodies that ensure those materials are for scientific research.

The world's largest particle detector

The other large balloon in the works out at McMurdo was ANITA-3, which flew earlier this week.  When we were in McMurdo, my colleague Abby Vieregg gave us a tour.  ANITA (Antarctic Impulsive Transient Antenna) is flying over Antarctica and looking for radio signals from two sources:

1. Ultra high-energy cosmic neutrinos hitting the ice below.
2. Cosmic rays crashing into the atmosphere above the ice

Neutrinos are very light neutral particles that are notoriously difficult to detect, and no one has ever seen the ultra high-energy variety before.  Cosmic Rays are an old fashioned name for high-energy protons of still unknown origin.

The picture above shows the ANITA balloon payload (taken from an article run in the Economist), and it looks like a Christmas tree of antennas.  Each of those square fixtures is an antenna designed to look at 300MHz-1GHz frequencies-- near where your cell phone operates.  In the picture, the payload is going through a “hang test” to check both weight and mechanical integrity prior to launch.

When neutrinos crash into the Antarctic ice cap, they collide with atoms to form a shower of charged particles, which then emit a cone of radio waves.  The polarization (direction the electric fields shake on the radio wave) is vertical and that's why those antennas have two fins.  The vertical one is meant to look for these radio waves generated by neutrinos whereas the horizontal fins should not see effects from neutrinos.

On the other had, cosmic rays seldom make it all the way to the surface of the Earth.  Instead, they hit gas in the atmosphere and produce their own shower of air born charged particles.  Those particles then spin around the Earth’s magnetic field and emit their own radio waves known as synchrotron.  Remember that at the South Pole, those fields are vertical – perpendicular to the Earth’s surface—which means the synchrotron radio waves are horizontally polarized.  So the ANITA team uses the other fin in each antenna to watch for that.

The instrument will fly for a 4-5 weeks over Antarctica, but by comparing all the antennas and rejecting data with no interesting events, they expect to record only 5-10 seconds of data over the entire time.  Each event will span only a few milliseconds, so this flight will hopefully provide thousands of events to consider.

Why bother doing this experiment?  One reason is that we don't know where cosmic rays come from, in part because those particles themselves are charged and can get whipped around by our galaxy’s magnetic fields, obscuring their origin.  But scientists strongly suspect that the ultra-high-energy neutrinos have a similar source.  Since neutrinos are neutral, they will ignore our galaxy's magnetic fields and their paths may point directly to their origin.  Scientists certainly haven’t found any nearby sources of these cosmic rays or neutrinos and we suspect that they should scatter off the microwave background if they come from really far away.  So we really don’t have a good guess of where they come from or what accelerated them to such high energies.

But there’s an even bigger long-term reason to do this.  Each of these neutrinos have nearly a Joule of energy – comparable to the energy of a 60mph baseball—packed into one of the lightest things in the universe.  That’s several hundred times more energy than the world most powerful particle accelerator can squeeze into each particle.  If these neutrinos interact with the ice or Earth and the ANITA team sees radio wave from that, they will be exploring the rules of particle physics far beyond what can be done in the lab.  And if they see enough events, then they may be able to use their data to test for deviations from those expected rules.  We’re all hoping that they someday find such a discrepancy because such a discovery might inspire the next generation of accelerators, experiments.  But for now, we have to wait and see if they can even detect these particles.

A tour of the Dark Sector Laboratory

I spend most of my time working in the Dark Sector Laboratory (DSL).  This photo was taken by our winter-over Steffan Richter as the sun rose in September a few years back:

After six months of darkness, that sight must be a true relief.

The bandwidth through the satellite connections is too poor to upload videos from here, so I can’t send up a tour of the lab.  Fortunately, my friend Jon Kauffman helped make one a couple years ago shortly before we decommissioned the BICEP-2 experiment.  Check it out here:

That tour does not really talk much about the South Pole Telescope, which is the large dish on the side of the building in the background.  The South Pole Telescope is probably our fiercest and most competent competitor.  But since we work in such close proximity, we wind up being extensions of each other’s teams while we’re down here, sharing advice, hardware and even manpower when needed.  While both teams are out to “win,” we all want to win for the right reasons.  And since we’re packed in together in such a remote location, our teams enjoy a camaraderie not seen anywhere else in our field.

Our team is in the process of building a much larger telescope in the space that Jon shows in the video above.  BICEP-2 was designed to observe the sky at the color where the Cosmic Microwave Background is brightest-- 150GHz.  (that 150 times higher than your cell-phone’s carrier frequency).  BICEP-3 will map at 100GHz, but with five times the detectors.  This will let us better understand the origins of the signals our team has seen.  Are those signals from the early universe, glowing dust in our galaxy, or some combination of the two?  Or maybe something else...

Once completed, BICEP-3 will map the sky in conjunction with the Keck Array, another set of telescopes that our team runs out of an adjacent building called the Martin A Pomeritz Observatory (MAPO).  I made a tour video of that the last time I was down here, which you can see here:

NOTE: when I was filming the cameras up in the rotating mount, I was paying more attention to not getting my hand caught in the azimuth (left-right) drive than where I was pointing my camera.  So when I am describing the elevation drive that move the telescopes up and down, I was actually pointed at a tray full of cables.  Oops.