May 24, 2016
In the next frontier of particle physics, scientists with the Long-Baseline Neutrino Facility and associated Deep Underground Neutrino Experiment (LBNF/DUNE) hope to make discoveries about neutrinos that could answer fundamental questions about the origins of the universe, learn more about the properties of neutrinos and do further studies in proton decay. They will do this by sending a beam of neutrinos 800 miles through the Earth from Fermi National Accelerator Lab [FNAL] in Batavia, Ill., to underground detectors at the Sanford Underground Research Facility in Lead, S.D.
But before they can begin that work, they need to be sure the detectors and cryogenic systems will work the way they need them to. That’s where engineer David Montanari comes in.
Montanari, the cryogenics infrastructure project manager for the LBNF Far Site Facilities and the U.S. liaison at CERN for LBNF, oversees the design of the cryogenic systems that will cool and
purify the detectors. It’s a big experiment—DUNE will be 100 times bigger than any liquid-argon particle detectors that have come before—that requires big prototypes.
“Large cryogenis systems are not a mystery. They have been done before and they exist in the industry,” Montanari said. For example, he said, the gas industry uses large tanks to store and cool natural gas and move the liquefied version around the world. “There are large air separation plants where they’ve produced liquid argon and liquid nitrogen—the liquid gases that we use in our
experiments—and they can make it pure. The point is always that we want to make it super pure; that is what separates us from industry.”
DUNE scientists chose liquid argon for its ability to detect the different types of neutrinos. To keep it in a liquid state, it must be cooled to minus 300 degrees Fahrenheit (minus 184 degrees Celsius or 88 degrees Kelvin).
The large DUNE prototypes being designed now are not be the first. Scientists built and tested a small, 35-ton at Fermilab.
“This proves that that we can make a cryostat and we can put a detector inside and we can achieve the purity we need,” Montanari said. “Now, we want to do it bigger and and make sure the bigger
one is pure as well.”
The new prototypes will consist of a dual-phase detector that will contain argon in both its liquid and gaseous forms, and a single-phase detector that will need liquid argon only. Although the cryostats will be identical dimensionwise, they will have independent cryogenic systems designed to accommodate the needs of each.
“This is important because we want to optimize the design and construction,” Montanari said. “So, by the time we go to LBNF/DUNE, we know how to make it and how to make it faster and better.”
In a presentation at the recent DUNE Collaboration meeting, co-spokesperson Mark Thomson, professor of physics at the Universityof Cambridge, said the goal is to have the prototypes completed by the fall of 2018. “In comparison,” he said, “the Empire State Building was built in 400 days.”
It’s an aggressive timeline, but one with a purpose, Montanari said. The prototypes will be built at CERN and the Collaboration plans to use a particle beam producedby a particle accelerator to
test the prototypes. “The timing is essential because the DUNE collaboration wants to take physics data with the beam as long as there is a beam.”
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The Sanford Underground Research Facility in Lead, South Dakota, advances our understanding of the universe by providing laboratory space deep underground, where sensitive physics experiments can be shielded from cosmic radiation. Researchers at the Sanford Lab explore some of the most challenging questions facing 21st century physics, such as the origin of matter, the nature of dark matter and the properties of neutrinos. The facility also hosts experiments in other disciplines—including geology, biology and engineering.
The Sanford Lab is located at the former Homestake gold mine, which was a physics landmark long before being converted into a dedicated science facility. Nuclear chemist Ray Davis earned a share of the Nobel Prize for Physics in 2002 for a solar neutrino experiment he installed 4,850 feet underground in the mine.
Homestake closed in 2003, but the company donated the property to South Dakota in 2006 for use as an underground laboratory. That same year, philanthropist T. Denny Sanford donated $70 million to the project. The South Dakota Legislature also created the South Dakota Science and Technology Authority to operate the lab. The state Legislature has committed more than $40 million in state funds to the project, and South Dakota also obtained a $10 million Community Development Block Grant to help rehabilitate the facility.
In 2007, after the National Science Foundation named Homestake as the preferred site for a proposed national Deep Underground Science and Engineering Laboratory (DUSEL), the South Dakota Science and Technology Authority (SDSTA) began reopening the former gold mine.
In December 2010, the National Science Board decided not to fund further design of DUSEL. However, in 2011 the Department of Energy, through the Lawrence Berkeley National Laboratory, agreed to support ongoing science operations at Sanford Lab, while investigating how to use the underground research facility for other longer-term experiments. The SDSTA, which owns Sanford Lab, continues to operate the facility under that agreement with Berkeley Lab.
The first two major physics experiments at the Sanford Lab are 4,850 feet underground in an area called the Davis Campus, named for the late Ray Davis. The Large Underground Xenon (LUX) experiment is housed in the same cavern excavated for Ray Davis’s experiment in the 1960s.
LUX/Dark matter experiment at SURF
In October 2013, after an initial run of 80 days, LUX was determined to be the most sensitive detector yet to search for dark matter—a mysterious, yet-to-be-detected substance thought to be the most prevalent matter in the universe. The Majorana Demonstrator experiment, also on the 4850 Level, is searching for a rare phenomenon called “neutrinoless double-beta decay” that could reveal whether subatomic particles called neutrinos can be their own antiparticle. Detection of neutrinoless double-beta decay could help determine why matter prevailed over antimatter. The Majorana Demonstrator experiment is adjacent to the original Davis cavern.
Another major experiment, the Long Baseline Neutrino Experiment (LBNE)—a collaboration with Fermi National Accelerator Laboratory (Fermilab) and Sanford Lab, is in the preliminary design stages. The project got a major boost last year when Congress approved and the president signed an Omnibus Appropriations bill that will fund LBNE operations through FY 2014. Called the “next frontier of particle physics,” LBNE will follow neutrinos as they travel 800 miles through the earth, from FermiLab in Batavia, Ill., to Sanford Lab.