Roza Doubnik

Liquefied ultrapure noble gases are typically the chosen target for neutrino and dark matter experiments. Commonly, the required grade of purity of such cryogenic liquids in terms of O₂ contamination is less than 100 ppt, which makes it necessary for the argon to circulate through adsorption columns filled, typically, with BASF Cu-0226S and Mol Sieve 4A for capturing O₂ and H₂O. Another requirement that emerged during the design of LBNF-DUNE is the purity of the Liquid Argon (LAr) in terms of N₂ concentration, as it was observed that both N₂ and O₂ contaminations can cause the reduction of the LAr scintillation light emission. In particular, a decreasing behavior in the lifetime and the relative amplitude of the slow component is relevant from concentrations of 1 ppm of N₂ and 0.1 ppm of O₂. Recently, exploratory experiments performed in the Liquid Argon Purification Cryostat (PuLArC — ∼90 L of LAr) had been successfully used to purify LAr from N₂ using an innovative solid adsorbent based on a Li-FAU Molecular Sieve. Here, we report experiments of N₂ capturing in LAr carried out at the ICEBERG Cryostat (∼3000 L of LAr) at Fermilab. For the experiments, several controlled injections of N₂ were made into the cryostat, and the impurity concentrations in the LAr (both for N₂ and O₂) were monitored using a calibrated gas analyzer during the purification process. The experimental data confirmed that the Li-FAU is capable of capturing the N₂ from the LAr. A numerical methodology based on the mass and energy balances of the system was applied to better understand the behavior of the adsorption process and to help with the scale-up of the process. A Pore Diffusion Model (PDM) coupled with parameter optimization was proposed to predict the N₂ concentration in the ICEBERG cryostat over time. The model parameters applied in this work were determined based on experimental data acquired in the PuLArC. The model was able to accurately reproduce the data from the ICEBERG, indicating that the mathematical model could be a valuable tool to design and operate the GAr/LAr system of LBNF-DUNE. It was possible to predict from simulations the necessary time to reach the required purity from an initial contamination concentration and also the number of purification cycles until solid saturation.

In this work, we unveil the potential of nitrogen (N₂) adsorption from Liquid Argon (LAr) through the molecular sieves (zeolites) Li-FAU Adsorbents. We report detailed studies about N₂ gas adsorption at T = 89 K using a commercial Micromeritics ASAP-2420 equipment and N₂ purification from LAr using the Purification Cryostat (PuLArC) at IFGW/Unicamp. We argue that the N₂ adsorption by the Li-FAU is possible thanks to the stronger interaction of N₂ with the lithium cations present in zeolite Li-FAU. In fact, the experiments performed in PuLArC have unequivocally shown that the Li-FAU adsorbent was capable of capturing N₂, reducing a N₂ contamination of 20–50 ppm to 0.1–1.0 ppm in 1–2 hours of circulation time in LAr for several runs. This result demonstrated the great potential of the Li-FAU adsorbent for N₂ capturing in LAr and invoke further tests of this material in larger scale LAr cryostats in order to confirm the innovative proposal of using the Li-FAU molecular sieve in replacement of Molecular Sieve 4A, currently used in LAr cryostats for neutrino experiments.

DUNE is an international experiment dedicated to addressing some of the questions at the forefront of particle physics and astrophysics, including the mystifying preponderance of matter over antimatter in the early universe. The dual-site experiment will employ an intense neutrino beam focused on both a near detector and a cryogenic far detector. The DUNE far detector implements liquid argon time-projection chamber (LArTPC) technology, and combines many tens-of-kilotons of fiducial mass with sub-centimeter spatial resolution to collect neutrino events and image them with high precision. Given its size, this detector will be implemented as a set of up to four modules, each of which will require its own cryostat that will contain approximately 17.5 metric kilotons of ultra-pure liquid argon (LAr). The cryogenics infrastructure to support the detector modules includes systems to receive, transfer, store, purify, and maintain the LAr. This design report describes the cryostats and the cryogenics infrastructure required for the first two detector modules; this infrastructure is designed to support expansion to up to four far detector modules.

The U.S. Department of Energy's Office of Scientific and Technical Information

The Long Baseline Neutrino Facility (LBNF) serves to provide the infrastructure necessary to support the Deep Underground Neutrino Experiment (DUNE), a growing international experiment to study neutrino science and proton decay. Situated at the Sanford Underground Research Facility (SURF), in Lead, SD, USA, DUNE will employ detectors located within massive cryostats filled with a total of 68,400 tons of ultrapure liquid argon. LBNF provides the cryogenic infrastructure necessary to supply and maintain that argon throughout the life of DUNE, as it enables the study of neutrinos from a new and improved beamline from Fermilab, as well as the dynamics of supernovae responsible for producing the heavy elements necessary for life and the possibility of proton decay. This contribution presents the modes of operation, layout, and main features of the cryogenic systems at LBNF. Those systems expected performance, functional requirements, and overall design status is also featured.