Mining noble gas: How astroparticle physics’ hunt for underground argon helped ease the global helium shortage

Underground, in Doe Canyon Deep Unit in Dolores County, Colorado, there is a reservoir of gas – carbon dioxide mainly, but also traces of helium and argon. It’s the presence of these noble gasses that sparked the interest of astrophysicists around the world and helped to ease the global helium shortage that has sent prices sky high in recent years. But a carbon-mining operation, which turned into an argon motherlode for astroparticle physicists, is helping to ease the shortage that sent prices sky high and had labs across the US shutting down important equipment.

Dr. Christiano Galbiati, a Professor of Physics at Princeton University, has been interested in finding a source of underground argon for a while. Argon, an inert noble gas, is often used as a target material for dark matter experiments. One of the inherent challenges of designing dark matter detectors is reducing the radioactive background activity to levels far below those on Earth’s surface. Usually, argon is pulled out of the atmosphere for use in detectors. However, atmospheric argon has been exposed to cosmic radiation so its background levels are higher than researchers would like. Underground argon, protected from cosmic radiation, would allow scientists to build an experiment with lower background levels which would in turn generate better data. Galbiati took the lead on a team of researchers exploring possible sources of underground argon. Their goal was to determine if such a source existed, and, if it did, whether the argon could be purified for use in a detector.

Galbiati’s team approached many companies about the possibility of exploring their gas wells for argon; Kinder Morgan’s Colorado site was one of the few to respond positively. They gave physicists access to their site and asked that in their search for argon they also verify the previous tests for traces of helium. 

Why does helium matter? Helium is used to cool magnets in MRI machines, and in a number of important pieces of equipment in labs around the country. The shortage of helium doesn’t just affect floating balloons: many university labs are shutting down valuable pieces of equipment because of the soaring costs of the helium required to keep them cool during operation.

It turned out that the Doe Canyon gas stream did indeed contain argon, and helium. Kinder Morgan allowed a third party to extract the helium, while physicists worked on purifying the argon.

A third-party helium recovery plant is operational on the site, producing up to 15% of the entire US supply of helium. 

Henning Back is a physicist at the Pacific Northwest National Laboratory. In January 2010, while working at Princeton, he got involved with the efforts to purify the argon from the Kinder Morgan wells. He spent five years developing purification processes; distilling in total 150 kg of argon.  This argon was then shipped to Gran Sasso laboratory where it became the target material in the DarkSide 50 dark matter experiment, for which Dr. Galbiati was the PI. 

The DarkSide 50 experiment served as a proof of concept – it showed that the argon from the wells in Colorado was significantly less radioactive than atmospheric argon, and that this low-radioactivity argon could be used in physics experiments requiring ever-lower backgrounds to hunt for dark matter. 

The next iteration of the experiment, DarkSide 20K, will require 50 tons of argon. Back laughs as he explains, “it took me five years to produce 150 kg of argon. The new plant will produce that much in half a day.”

Galbiati is quick to credit Kinder Morgan for their participation, and grateful for the ongoing positive relationship between Kinder Morgan and Fermilab. Currently, argon production is on hold while a new plant is constructed at the Colorado site. It is slated to be completed in 2020, and when fully operational should produce 300 kg of argon per day.

As it turns out, this site is the first of its kind in several ways: the first helium recovery plant that uses CO2 capture for production, and the first plant for underground argon production. The long-term impacts of this project are ongoing: the United States Congress passed a bill allowing for increased exploration of helium sources, while within the physics community interest in underground argon has increased – several more experiments have discussed the possibility of using it as a target material in future detectors. Says Back, “we’re all very happy with the science that we do, but everyone gets excited when their work has a much more immediate societal impact.”

– Jenna Saffin