In mid-May, Fermilab Director Lia Merminga, LBNF/DUNE project members and other staff welcomed LBNF/DUNE collaborators from Brazil for a four-day visit to observe cryogenics prototyping efforts and the various liquid argon detectors and research facilities at the lab, and to promote the ongoing partnership between Fermilab and the collaborating Brazilian institutions.
DUNE’s cryogenics systems and Brazilian collaborators’ contributions
The Deep Underground Neutrino Experiment far detector will be the world’s largest cryogenic particle detector. Split into four modules to be installed a mile underground at the Sanford Lab in South Dakota, each module is designed to house a neutrino detector immersed in an enormous vat of cryogenic liquid argon. Everything that goes into constructing and eventually servicing these modules will have to travel down a narrow access shaft once it arrives at SURF. This includes the equipment required to keep the argon at the right temperature and purity, which is crucial for the detector’s ability to detect neutrinos.
For each module, about 1,000 tanker trucks will deliver liquid argon to SURF over the period of about a year. Equipment near the top of the access shaft will vaporize the argon. The argon gas then will be transferred down the shaft, and recondensing equipment will reliquefy it underground. Once a detector module is fully installed, it must be made free of all debris that could contaminate the argon. At that point, the cryogenics systems will begin to push out the air, cool the volume, then fill it with a volume of purified liquid argon sufficient to fill about five-and-a-half Olympic-sized swimming pools—a year-long process.
During this filling phase, a set of pumps will begin circulating the liquid through a purification filter. A minuscule but unavoidable heat ingress will cause a very slow, constant evaporation of the liquid, which in turn will lead to the need for vapor recovery and a reliquefaction process. These processes will run continuously for the roughly two-decade planned duration of the experiment.
The Long-Baseline Neutrino Facility is providing the cryogenics infrastructure for the DUNE experiment. Experiment collaborators Campinas State University (UNICAMP) of São Paulo, Brazil, and Akaer Group, a corporate partner in Brazil, will supply the purification systems for the first two far detector modules for both the gaseous and liquid argon, as well as the liquid argon circulation pumps. For the second module, UNICAMP will also supply the recondensation system for the evaporated gas. São Paolo Research Foundation (FAPESP) is providing in-kind contributions to this portion of the LBNF/DUNE project.
The liquid argon purification systems use filters consisting of a molecular sieve and copper pellets that remove contaminants from the argon. These filters will regularly saturate and require a cleaning process that is referred to as regeneration. It involves heating the filter with a hydrogen-argon mixture to vaporize any trapped water and oxygen, then using a heat exchanger to cool the filter again to liquid argon temperature (-303 degrees F, 87K) so it is ready to be put back into use.
Researchers at UNICAMP are exploring alternate purification media for the LBNF/DUNE argon purification and filter regeneration system, including filter media to capture nitrogen from liquid argon, a highly desirable feature that does not currently exist in any of the ongoing prototyping experiments at Fermilab or at CERN. They have identified some promising materials for both nitrogen and higher oxygen capture. The materials still require testing in UNICAMP’s ~200-liter cryostat; to be accepted, any new material’s oxygen-capture performance would need to match or exceed that of the media already used in the prototypes.
Brazilian VIP visit
Roza Doubnik, the LBNF/DUNE point of contact with Brazil’s in-kind contributors, organized the visit and prepared the tours. The LBNF/DUNE cryogenics team, headed by David Montanari, along with several Fermilab scientists and engineers from Neutrino Division, provided tours and demonstrations to the Brazilian visitors: Dilson Cardoso of the Federal University of São Carlos; Pascoal José Giglio Pagliuso of UNICAMP; Krystal Brant Oliveira of the Brazilian Center for Physics Research; and Fernando Coelho Ferraz of Akaer Group.
During the course of the visit, the delegation toured the ICARUS detector, examined relevant features of the cryostat, viewed the MicroBooNE liquid argon circulation system, and visited the test facilities for liquid argon and filtration media, as well as active test setups and experiments related to the LBNF/DUNE Project in PAB. They also enjoyed meeting the Brazilian students and post-docs who are making important contributions to the SBND installation, and seeing their work.
The visitors found the tours and discussions at Fermilab extremely productive, according to Doubnik, and they left feeling inspired about the contributions they will make to help enable DUNE’s neutrino science program.