Pascoal G. Pagliuso

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 have explored the potential of oxygen capture in Liquid Argon (LAr) of the innovative CuO dispersive layered double hydroxide media (R-LDH) and the Ce-doped R-LDH. Low-temperature experiments in the LAr Purification Cryostat (PuLArC) at IFGW/Unicamp were performed using LAr circulation through two filters, one containing the R-LDH (or the Ce-doped R-LDH) material and the other the BASF commercial copper material (Cu-02265 — proposed as a reference O₂ getter media by Fermilab) for comparison. Interestingly, the experiments performed in PuLArC revealed that the R-LDH and Ce-doped R-LDH innovative media were capable of capturing O₂ from recirculating LAr in PuLArC. For instance, the R-LDH media reduced the O₂ contaminants concentration by 80% of its initial values after 200 min of LAr circulation. As for the reference media BASF Cu-S0226, this media reduced the O₂ concentration by 40% of its initial value in the same time window. The performance/kg of the studied media will be compared and we will discuss the putative higher potential of the innovative Ce-doped and pure R-LDH media for O₂ capturing in LAr which may invoke further tests of these media in larger scale LAr cryostats, possibly at Fermilab and CERN.

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.

In the ferromagnetic Weyl semimetal CeAlSi both space-inversion and time-reversal symmetries are broken. We use external pressure as an effective tuning parameter and relate three observations to the presence of a nontrivial topology in its ferromagnetic regime: an exceptional temperature response of the quantum oscillations amplitude, the presence of an anomalous Hall effect (AHE), and the existence of an unusual loop Hall effect (LHE). We find a suppression of the AHE and the LHE with increasing pressure, while the Curie temperature is enhanced. The magnetic structure and the electronic bands exhibit only a negligible pressure effect suggesting the importance of the domain wall landscape for the topological behavior in CeAlSi.

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