In the United States, a highly intriguing initiative involving the usage of a lot of argon is now ongoing. The Long-Baseline Neutrino Facility (LBNF) and Deep Underground Neutrino Experiment (DUNE), a worldwide flagship effort to unravel the mysteries of neutrinos, is the biggest particle physics project ever constructed in the United States.

The project’s objectives are lofty. Its goal is to see whether neutrinos are the reason the cosmos is made up of stuff. It seeks for subatomic events that might aid in the realization of Einstein’s idea of unifying forces.

It will also investigate and analyze neutrinos produced by a particle accelerator at the US Department of Energy’s Fermilab in Batavia, Illinois, as well as neutrinos emitted by supernovas. A neutrino is a subatomic particle that is very difficult to detect while being one of the most prevalent particles in the universe. The DUNE distant detector will be housed in the Sanford Underground Research Facility (SURF), a mile underground laboratory in Lead, South Dakota, run by the LBNF. From Fermilab’s 6,800-acre location in Batavia to SURF, a stream of neutrinos will be sent 800 miles through the Earth.

An innovative experiment

Since 2015, Fermilab has received advice on the DUNE experiment from J.R. (Buzz) Campbell, co-founder of Intelligas Consulting and a recognized specialist on industrial gases. His job is to act as a liaison between Fermilab and the commercial sector for anything cryogenic or involving the usage of gases in this project.

“The science and technology underlying the detector’s design is ground-breaking,” Campbell added. It’s similar to a moonshot. To make this experiment viable, scientists and engineers working on this project must create new systems and technologies. And it all needs to be planned and constructed to work at SURF, which is 5,000 feet deep. To create room for the experiment and the enormous cryostats, teams are now digging and removing 800,000 tons of rock.”

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The solid granite at SURF protects the experiment from high-energy particles and cosmic radiation, which may distort findings, but it makes planning and constructing the experiment very difficult. “The elevator shaft, which runs down 5,000 feet, had to be particularly designed to accommodate extremely big weights and enormous size pieces for the experiment’s construction,” Campbell said. The movement of such items and equipment must be accommodated in the subterranean area being dug.”


Source: Fermilab
Deep Underground Neutrino Experiment; one of four detector modules in South Dakota

Argon is in short supply

The DUNE experiment, which will be made up of four modules containing 17,400 tons of liquid argon each, will be centered on argon (LAR). The detectors will focus a stream of neutrinos towards the argon and record neutrino interactions with unparalleled accuracy using sophisticated technologies. “Liquid argon is a dazzling fluid, that is, it is readily excited,” Campbell explained. When a neutrino collides with an argon atom, it produces an electron and other subatomic particles that may be studied.”

By 2027-2028, two argon-filled distant detector cryostats should be operational. DUNE will eventually consist of four distant detector cryostats containing roughly 70,000 tons of LAR, as well as a smaller near detector at Fermilab. Before the cryostats can be filled, additional argon will be needed to purge and chill them down. Reliquefying the heat-leaked argon gas from the cryostats and recycling it is an ongoing element of the project.

“While over 70,000 tons is a lot of liquid argon, the US utilizes roughly 1.4 million tons a year, all generated as LAR, but most consumed as a gas,” Campbell said of the project’s argon market ramifications. This amount of argon is tiny in comparison to overall US consumption, and it will be utilized over a four-year period.”

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The distance complicates the argon supply chain for this project. “There isn’t much liquid argon capacity within 500 miles of the Lead site,” Campbell said. This implies that the LAR will be transported across great distances by truck or train. The system is capable of receiving 2-4 road tanker cargoes each day.”

In Lead, there will be a lot of LAR storage around the shaft opening. “The LAR will be brought to the location, then vaporized above ground,” Campbell added. The argon will be transported 5,000 feet down a unique shaft and reliquefied below ground before being piped to the cryostats via a complex vacuum jacketed (VJ) piping system. The gaseous argon down shaft is liquefied using a nitrogen liquefier. This subterranean system is unlike any other in terms of scale and scope that has ever been developed and operated underground.”


Maintaining the purity of the argon is one of the most difficult aspects of the experiment. “In this experiment, argon purity levels are assessed in parts per billion,” Campbell said.

“Oxygen reduces the argon’s sensitivity. As a result, the experiment will include a one-of-a-kind subterranean purifying system. The purity needed for the experiment will be comparable to that of electronic grade argon, but the flow rate will be significantly greater. For this study, DUNE scientists had to create very sophisticated oxygen detectors.”

“A significant component of the experiment is the dependability of the overall system’s design, construction, and operation at 5,000 feet down shaft, with limited access,” Campbell says. Above ground, at vendor facilities, the equipment will be planned, produced, and tested before being brought to the site. It will then be dismantled and hauled down shaft before being rebuilt and tested. The dependability of all of this, as well as its functioning, is critical to DUNE’s success.”

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The project is still under progress

Liquid argon will not be available for some years. Meanwhile, the facilities, cryostats, and all of their supporting equipment, including miles of vacuum jacketed pipe, are being developed and will be completed on time. We’ll keep readers updated on the progress of this fascinating project.


Photo-Source: Fermilab

Shimmering liquid argon is visible inside the Liquid-Argon Purity Demonstrator, a 35-ton-capacity prototype cryostat used for early tests of LBNF/DUNE

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