There is a very exciting project underway in the US that involves the use of lots of argon. The construction of the Long-Baseline Neutrino Facility (LBNF) and the Deep Underground Neutrino Experiment (DUNE), an international flagship collaboration to unlock the mysteries of neutrinos, represents the largest particle physics project ever built in the US.
The project’s goals are ambitious. It seeks to find out whether neutrinos could be the reason the universe is made of matter. It looks for subatomic phenomena that could help realize Einstein’s dream of the unification of forces.
And it will study and analyze neutrinos emerging from supernovas, as well as the neutrinos generated by a particle accelerator at the US Department of Energy’s Fermilab in Batavia, Illinois. A neutrino is a subatomic particle, and, while it is one of the most abundant particles in the universe, it is incredibly difficult to detect. LBNF will house the DUNE far detector at the Sanford Underground Research Facility (SURF), a mile underground laboratory in Lead, South Dakota. A stream of neutrinos will be beamed 800 miles through the Earth from Fermilab’s 6,800-acre site in Batavia to SURF.
A ground-breaking experiment
J.R. (Buzz) Campbell, co-founder of Intelligas Consulting and a leading expert on industrial gases, has been advising Fermilab on the DUNE experiment since 2015. His role is to serve as the interface between the private sector and Fermilab for anything that is cryogenic and involves the uses of gases in this project.
Campbell said, “The science and technology behind the creation of the detector is ground-breaking. It’s like the moonshot. Scientists and engineers on this project have to develop new systems and technology to make this experiment possible. And this all has to be designed and built to be operational 5,000 feet underground at SURF. Right now crews are excavating and removing 800,000 tons of rock to make space for the experiment and the large cryostats.”
The dense rock at SURF shields the experiment from high-energy particles and cosmic radiation that can skew results, but makes the logistics of designing and building the experiment very challenging. Campbell related, “The elevator shaft goes down 5,000 feet and had to be specially modified to carry very heavy loads and large scale parts for the construction of the experiment. The underground space being excavated has to accommodate the movement of those parts and equipment.”
Argon is at the heart of the DUNE experiment, which will be comprised of four modules that each contains 17,400 tons of liquid argon (LAR). The detectors will direct a beam of neutrinos at the argon, and using advanced technology, will record neutrino interactions with unprecedented precision. Campbell said, “Liquid argon is a scintillating fluid, that is, it is easily energized. When a neutrino hits an atom of argon it generates an electron and other sub-atomic particles which can be analyzed.”
Two far detector cryostats filled with argon are expected to be online by 2027-2028. Ultimately, DUNE will comprise four far detector cryostats, filled with a total of about 70,000 tons of LAR, and the smaller near detector at Fermilab. Even more argon will be required to purge and cool down the cryostats before they are filled. An ongoing part of the project is to reliquefy the heat-leaked argon gas from the cryostats and recycle it back to them.
Regarding the argon market implications of this project, Campbell explained, “While over 70,000 tons is a lot of liquid argon, the US uses about 1.4 million tons a year, all produced as LAR, but most used as a gas. This volume of argon relative to total US demand is small and it will be used over four years.”
The supply chain for argon for this project is complicated by distance. Campbell reported, “There isn’t much liquid argon capacity within 500 miles of the Lead site. This means that the LAR will be trucked, or perhaps railed, over long distances. The system is designed to take delivery of 2-4 road tanker loads per day.”
Substantial LAR storage will be located near the entrance to the shaft in Lead. Campbell explained, “The LAR will be delivered to the site, then vaporized above ground. The gaseous argon will be piped 5,000 feet down through a special shaft and reliquefied below ground before being piped through an extensive vacuum jacketed (VJ) piping system to the cryostats. A nitrogen liquefier is being used to liquefy the gaseous argon down shaft. This underground system is of a unique size and scope, unlike any ever built and operated underground before.”
One of the significant challenges of the experiment is maintaining the purity of the argon. “Purity levels for argon in this experiment are being measured in parts per billion,” said Campbell.
“Oxygen decreases the sensitivity of the argon. For this reason, the experiment will have a unique underground purification system. The purity required for the experiment will be similar to electronic grade argon but will have much higher flow rate. DUNE scientists have had to develop highly specialized oxygen detectors for this project.”
According to Campbell, “The reliability of the whole system’s design, build, and operation at 5,000 feet down shaft, with restricted access, is a critical part of the experiment. The equipment will be designed, built, and tested above ground in vendor facilities, and shipped to the site. It then will be disassembled and transported down shaft, where it will be reassembled and retested. The reliability of all this and its operation is a key factor in DUNE’s success.”
The work continues
The delivery of liquid argon is still a few years out. In the meantime, the design of the facilities, cryostats, and all of their supporting equipment, including miles of vacuum jacketed piping, are in development and on schedule. We will keep readers informed of this exciting experiment as it unfolds.
Using gases to generate a wave of plasma
The Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) recently announced the next phase in the development of laser-plasma particle accelerators (LPAs) is underway. This project represents a new approach to high-power lasers. It combines the pulses from many fast-acting but lower-energy optical fiber lasers, and is designed to energize super-compact accelerators.
gasworld spoke to Berkeley Lab scientists Jeroen van Tilborg, Tong Zhou, Eric Esarey and Cameron Geddes, director of Berkeley Lab’s Accelerator Technology and Applied Physics (ATAP) Division, to learn more about the LPA project and the gases used in this technology.
What makes this project a new approach to high-powered lasers ?
Berkeley Lab (BL): Our fiber demonstrations provide a path to combining high peak power and high average laser power, at high efficiency, as is needed for high performance plasma-based accelerators.
LPAs offer an alternative way to accelerate and boost the energies of the particles. Rather than using microwaves, an intense beam of laser light is fired through a gas. This generates a plasma wave that charged particles can ride like a surfer. What gases are used?
BL: A broad range of gases are of interest. We typically use pure helium (He) or pure hydrogen (H2). We have found it advantageous to use a mix of He and nitrogen (N2), as well. Novel injection schemes might open up applications of other gases like krypton and argon.
What are some of the challenges related to gas use in the development of these LPAs?
BL: A gas target is ionized to form the plasma in which the acceleration process happens. The gas target itself requires careful design and flow analysis to deliver the desired density and profile. The biggest issue is not so much gas delivery to the accelerator, but dealing with the gas load in the vacuum chambers – the gas must be removed from all regions except the desired target area to allow the laser to focus properly. This is true especially for continuous-flow to provide gas for >kHz repetition rate systems as will be enabled by fiber lasers, and which will, in the future, will require sophisticated gas capture systems. Control over gas mixture is important as well. For example, 0.5% N2 in He might behave differently as an accelerator when compared to 0.6% N2 in He.
Do LPAs use large volumes of gas?
BL: Currently we are using only a small volume at the level of one bottle every two weeks. However, continuous flow systems will use several orders of magnitude more of gas. They will likely require systems to recapture gas from the jet while preserving the surrounding vacuum, to dissipate kW-class heat loads from the recovered gas, and to recycle it.
What are some of the possible new applications for these more sophisticated LPAs?
BL: We are excited about possible application in areas like higher resolution medical imaging, medical radiation therapy, high-energy-density science, high throughput micro-electronics 3D characterization, advanced manufacturing capabilities, nuclear nonproliferation, and homeland security cargo inspection to name a few. Ultimately these LPAs might even be the basis for a new generation of colliders, orders of magnitude smaller - or higher in energy - than today’s, for high-energy physics. Laser-driven colliders require powerful lasers and a high repetition rate. From a simple wall-plug power scaling, this demands a dramatic increase in efficiency of laser-plasma accelerators (from wall-plug to the electron beam).
Fiber lasers can address this increase in efficiency.