Ice Stories: Dispatches From Polar Scientists » Dark Sector Laboratory

Climactic Success

Kathryn Schaffer Miknaitis — Thu, 07 Feb 2008 14:06:59 +0000

Everyone here is breathing a huge sigh of relief. Last night was the first night that our new set of detectors were cold enough to be operated. Unlike the last few test runs, for this run we had mounted the receiver up in the telescope where it normally lives, in preparation for doing real observing. As soon as the detectors were tuned, we pointed the telescope at an object in the sky called RCW38, which is a bright source of radiation at the frequencies we observe.

One layer of the new receiver. The small, single millimeter-wide circles at the top are our ultra-sensitive detectors.

We made a beautiful map of RCW38 and began learning about the properties of our new detector array, which looks fantastic. We still have a lot to learn before we leave, but last night was the big test, and possibly the most exciting moment of the whole season. We celebrated our success by sipping champagne out of paper cups while we looked at our very first data from the upgraded instrument. The enormous efforts that went into the upgrades this year look like they’re going to pay off!

The complete rebuilt receiver.

Our New Sunroof

Kathryn Schaffer Miknaitis — Sat, 05 Jan 2008 14:21:41 +0000

It’s been a busy couple of weeks out at the telescope. SPT postdoc Brad Benson and graduate students Martin Lueker and Joaquin Vieira installed a new set of detectors into the SPT “receiver,” which is essentially the camera for the telescope. A full array of detectors for our receiver consists of 1,000 individual pixels. Each pixel is an exquisitely sensitive device that registers tiny temperature changes when it absorbs electromagnetic radiation like that from the early universe. We record electrical signals that tell us essentially how much heat each detector has absorbed as we scan the telescope to point at different locations in the sky. For now, however, what we are interested in doing is testing the new detectors without installing them in the telescope itself, and just seeing how they work. These detectors are a major research project in themselves, and each batch incorporates new features as we learn more and more about their performance.

Because these new detectors are so sensitive, the radiation from any warm object in their field of view can overwhelm them–essentially they overheat. For the tests that we wanted to perform, we installed the receiver on the optics cryostat, which holds the 1-meter secondary mirror for the telescope, and usually lives up in the big boom below the dish. We needed a way to point the window in the optics cryostat out at the sky without mounting it back up into the telescope. So, what we’ve been doing is opening up the sliding roof above the control room and using a big metal plate to bounce light from the sky into the optics cryostat, and eventually to the detectors. The sky is the coldest thing around, and it’s also what the detectors are designed to see.

Our sunroof. The big white vessel is the cryostat that holds our secondary mirror at a low enough temperature (around ten degrees above absolute zero) that its own radiation doesn’t swamp our detectors. In this picture you can’t see the red receiver cryostat bolted to it on the other side–that’s what holds the detectors. The large silver box is the FTS, which I’ve described before. The big metal plate is what’s making sure that our detectors are mostly looking at the sky.

However, this has made for interesting working conditions in the lab. It’s nice to get the natural light in there, but with the ceiling open to the South Pole environment, it’s been freezing! For the last week I’ve been working in the control room at my laptop, controlling some of the tests and looking at data. I always have enough clothes on that I don’t feel cold, but I really notice how much harder it is to type. The fingers just don’t want to move quickly. At times, the wind was even blowing snow through the roof, and it was bizarre to have a bluster of ice flakes swirling around in the room.

We just finished two days of taking FTS measurements to characterize the response of the updated receiver to light of different frequencies. In the picture below you can see what it looked like from the other side of the setup.

The lenses and windows in the center of this picture are part of the setup used to direct just a little bit of light from the FTS instrument into the receiver, so that it’s not too much for the detectors to take. Mostly, the detectors are looking straight up into that sunny blue sky. We are working right under the telescope itself, and you can see the bottom of the telescope boom in the background. In this position, the telescope is on its back, with the dish staring straight up as well.

It’s been a busy but successful couple of weeks, and we’re about ready to close up the sunroof and move on to the next projects for the season. It’s never dull around here!

Dirt and Decay in the Clean Land of Ice

Kathryn Schaffer Miknaitis — Tue, 11 Dec 2007 16:17:29 +0000

The South Pole is one of the cleanest places I have ever been. Outside, the environment is absolutely pristine and essentially unchanging. There is no soil, no solid ground, no vegetation or animal life for many miles. There is no weather, except the wind blowing snow across the vast ice plateau. There is nothing for the wind to erode but the layers of ice and snow. There is nothing that disintegrates or decays or accumulates in the treads of your boots as you walk around outside. Any dirt or dust we encounter is due to our activities here and is made from the materials we import and use on the station.

The new station itself is kept exceptionally clean, so even the imported dust and grime is kept to a minimum. Everyone on station takes turns cleaning the bathrooms and common rooms, and a janitorial staff works around the clock to keep everything looking new.

So, it’s with some irony that I will also cite the South Pole as one of the dirtiest places I have been. Rather, I should rephrase that–it is the place where I am regularly dirtiest. All of our water on station comes from melting ice, and this requires a huge amount of energy. Consequently, there are stringent restrictions on water use. Yes, we have running water and modern comforts in the South Pole Station, but we are allowed to take no more than two two-minute showers per week. After a while, you get used to it, and your regular showers back home seems like an extravagant indulgence. But even so, there is something funny about the contrast between the scruffy, sweaty, unwashed population and our spotless station and pristine environs.

Because everything in the station is so new and clean, there is also something endearing about any object that has been here long enough to show wear and tear, decay and change. When I am not working out at the Dark Sector Laboratory next to the telescope, I set up my laptop in the science lab in the main station. Like every other portion of the station, this lab is spotless and new. It was with some perverse pride that I claimed for myself one of the oldest most pathetic chairs on station as my seat for daily work when I first got here. These supposedly were the chairs from the galley in the old dome, and have seen years of constant use.

My proudly chosen decaying chair, supposedly from the old dome galley.

A week ago, a shipment of brand-new chairs came in and we replaced all of the old chairs we had been using in the science lab. I helped to carry the old chairs out and place them in the ‘non-recyclable’ garbage bin out behind the station. It’s silly to develop affection for something so nasty and downright uncomfortable, but I was a little sorry to see the chair go. However, if there is one other fact of the South Pole it’s that anything useful gets reused until it completely falls apart. I have already spotted those chairs appearing in common spaces and personal spaces around the station, looking just as out of place in most of those as they did in our high-tech shining lab. Out of place, in a way, like all of our messy human activities in this stark white place.