Sergey Koshelev

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.

Fermi National Accelerator Laboratory (FNAL) and Lawrence Berkeley National Laboratory (LBNL) are building a new High Field Vertical Magnet Test Facility (HFVMTF) for testing superconducting cables in high magnetic field. The background magnetic field of 15 T in the HFVMTF will be produced by a magnet provided by LBNL. The HFVMTF is jointly funded by the US DOE Offices of Science, High Energy Physics (HEP), and Fusion Energy Sciences (FES), and will serve as a superconducting cable test facility in high magnetic fields and a wide range of temperatures for HEP and FES communities. This facility will also be used to test high-field superconducting magnet models and demonstrators, including hybrid magnets, produced by the US Magnet Development Program (MDP). The paper describes the status of the facility, including construction, cryostat designs, top and lambda plates, and systems for powering, and quench protection and monitoring.

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