Newswise — Two South Dakota State University mechanical engineering professors are part of an international team of scientists and engineers working to uncover details about how the universe was formed.
Associate professors Stephen Gent and Greg Michna are using SDSU’s high-performance computing cluster to predict how argon circulates within the particle detectors to be constructed one mile beneath the earth’s surface. These particle detectors will help physicists answer key questions about the Big Bang theory. The detectors are part of the Deep Underground Neutrino Experiment at the Sanford Underground Research Facility near Lead.
More than 1,000 scientists from 32 countries are working on the DUNE project, hosted by the U.S. Department of Energy’s Fermi National Accelerator Laboratory, known as Fermilab. The scientists are trying to figure out why the universe is made of matter rather than antimatter. It is suspected that neutrinos—tiny subatomic particles that can pass through matter, including people—tipped the scales in favor of matter 13.8 billion years ago.
The European organization CERN, which operates the world’s largest particle physics laboratory, is installing and testing the prototype detectors that DUNE scientists will use to ensure that all of the components work properly.
The prototype detectors have 800 tons of argon flowing through them. The liquid argon must be kept at temperatures below -186 degrees Celsius, which is approximately -303 degrees Fahrenheit.
“When a neutrino hits something, it gives off electrons. The electron lifetime is dependent upon the impurity levels of the argon (which flows through the detector),” Michna said. “There should be few impurities in the liquid argon and the distribution of impurities should be uniform.”
Since 2016, the SDSU researchers have been using sophisticated computer models to simulate the movement of argon in the detector through funding from Fermilab. They collaborate with DUNE scientists through the Cryogenic Instrumentation and Calibration Consortium.
"SDSU has greatly expanded the overall expertise in DUNE on fluid flow simulations,” said Fermilab’s Eric James, the technical coordinator for DUNE. “Understanding liquid argon’s behavior and developing expertise and accuracy in this area is essential as we move towards building the first multi-kiloton liquid-argon DUNE detector.”
Modeling flow of argon
Their work, thus far, has involved modeling argon flow in the single-phase ProtoDUNE particle detector. “We are simulating the impurity distribution in the detector, but ProtoDUNE has few purity monitors to compare to our model results,” Michna explained. Therefore, the researchers track changes in temperature as the argon flows through the detector. “If we have satisfactory accuracy on temperature, that validation of our model gives us better confidence in the impurity results predicted by our computer simulations,” Gent said.
“The scientists and engineers we are working with require a high level of accuracy—our model agrees with experimental measurements within 0.005 degrees Celsius. That is pretty demanding,” Michna said. He characterized their recent modeling work as being “less about informing the design choices and more in verifying that the design is doing what they think it is doing.” CERN has been operating the single-phase detector since September 2018.
Using high-performance computing
SDSU’s high-performance computing clusters have played a key role in the project. “If we did not have the HPC clusters, we would not be able to do this work, period,” Gent said. Prior to 2018, one simulation took a week or two. “Now we can measure that time in days rather than weeks.”
With this increased computing power, Gent said, “We are able to turn around data requests from collaborators much more quickly, oftentimes for the next weekly meeting with them.”
“Our work is having an impact on this unique international project,” Michna added.
“The simulation of the single-phase ProtoDUNE detector is mostly complete and working well,” said Gent. He and Michna recently received their third grant from Fermilab to continue their modeling work.
For the new project, the researchers will continue working on the single-phase detector and will begin simulating the dual-phase detector, which uses argon as a gas and a liquid. “It has different features inside so the flow is different,” Gent said. Consequently, they will need to change model geometry and look at how refined the computer model is in terms of grid size, boundary conditions and the interface between liquid and vapor. CERN began operating the prototype dual-phase detector in August 2019.
One graduate and one undergraduate student also work on the project. Cecilia Streff, who worked on the project as an undergraduate, will continue on the new grant as a master’s student.
“These projects offer students an opportunity to get a global perspective on how a very large project works,” Gent said. “The students gain experience reporting results via regular meetings with our partners and via technical reports shared with the DUNE community.”