Thread by @realscientists

Okay, so I've mentioned the IceCube Neutrino Observatory a few times now. I'm going to dive into this now that we've discussed neutrinos a bit more.

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The IceCube observatory is a permanent installation of sensors in the Antarctic Ice Sheet at the South Pole. There are a variety of reasons that make this an ideal locale for detecting high-energy neutrinos.

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First, the deep ice of the Antarctic Ice Sheet is one of the clearest mediums in the world; after thousands of years, any dirt/dust/particles that was trapped in the ice was eventually pushed to the edges due to sheer pressure.

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Having a clear medium is extremely important, as the interactions the detector is looking for are very small and could be obscured by small amounts of particles.

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Another reason the IceCube observatory is at the South Pole is due to the Amundsen-Scott South Pole Station: the station already facilitates many science experiments and has the logistical capability to support a large-scale installation such as IceCube.

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Obviously the Antarctic Ice Sheet is quite large, so technically this observatory could've been installed anywhere, but it required a large workforce, significant and reliable cargo transport, and resources such as lodging, food, etc.

All of which exist at the South Pole.

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Another reason the South Pole was an ideal location is due the depth of the ice; to shield the sensors from radiation that is prevalent at the Earth's surface, the sensors were placed at a depth between 1450m and 2450m.

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The sensors consist of PMTs that are encased in a glass sphere with DAQ boards inside; the entire assembly is called a Digital Optical Module, or DOM. Here's a picture!

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One might ask "How do you install the DOMs into the ice?" which is a perfectly reasonable question.

You drill a hole! That's where we come in.

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IceCube was a project that originated at the University of Wisconsin-Madison. One of the entities brought in to consult on the installation process was the Physical Sciences Lab (where I work.) We were brought in to devise a way to drill 2.5km into the ice.

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So the Physical Sciences Lab (PSL) designed and built a huge system called the Enhanced Hot Water Drill (EHWD.) The EHWD drilled 86 holes over 7 seasons. The water was heated to 88° C and then shot through a nozzle with a pressure of 1100 psig.

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I could go into a lot of the technical information of the EHWD system, but for now I'll stick to the basics. The EHWD was a huge success, it had a 92% thermal efficiency, and with a skilled drill team they drilled 20 holes in a single summer season.

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The EHWD doesn't actually require hot water to drill the hole, but with air temperatures sitting around -15° F/-26° C, water that isn't heated would freeze nearly immediately. The hole itself was produced due to the pressure of the water exiting the nozzle.

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The DOMs are attached in a string and lowered into the hole relatively quickly, because water is left in the hole to freeze the DOMs into place. Once the water is frozen, the DOMs become one with the ice. Here's a photo of a DOM before and during deployment.

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Fun fact: everyone at drill camp wears head protection, but due to an unfortunate incident we all wear climbing helmets with a chin strap. Can you guess the incident?

(Hint: it involves someone looking down into the hole while wearing a hard hat without a chin strap)

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Here's some photos from construction:
This is the tower, of which there are two. The tower supports the weight of the drillhead, the drill hose, the drill cable, and the DOM deployment.

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Here's a picture of the tower with the hose and cables in position.

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Here's a picture of the Main Hose Reel, which gets wrapped with nearly 10,000 feet of hose. (It is not wrapped with hose in this photo)

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So you might wonder why I'm involved in a project that completed construction in 2010?
The NSF has funded an upgrade to IceCube, called IceCube Upgrade (who could've guessed?) that will drill 7 additional holes during the 2022/2023 season.

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I was not involved in IceCube Gen1 (original project) as I was about 10 when they started it, but I am currently involved with the Upgrade. I went to the Amundsen-Scott South Pole Station this past season (Austral summer) for the Upgrade, and I will be a driller come 2022.

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We have a lot of work to do! All of our equipment was left at the South Pole when drilling was completed in 2010. So we go down there to check the status, perform upgrades and testing to check operational capability, etc.

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The Upgrade will deploy 7 additional strings that are updated with the new/current technology, as well as perform what's called "degassing" which attempts to eliminate air bubbles that accumulate during the refreeze process.

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Since we're only drilling 7 holes, it makes the most sense to just revive our original EHWD system rather than design and build a new one. Luckily, the South Pole is one of the best places in the world to store equipment.

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With minimal humidity (near 0%), almost no precipitation, and extreme cold temperatures, equipment tends to fare quite well compared to equipment stored elsewhere. The steel doesn't rust and there's minimal corrosion within the system.

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This is all the info I have time for, but I will add to this thread later! I'll do a thread specifically about the South Pole station and that experience so if you have questions, I will address that later. Go forth and excel today! (but wash your hands)

Oh also, one last tweet: for more information about IceCube, their website is excellent! Also give them a follow, they tweet awesome science.
icecube.wisc.edu @uw_icecube

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