Speaker
Description
Liquefied ultra-pure noble elements are typically used in neutrino and dark matter experiments. Achieving the necessary purity of these cryogenic liquids, particularly in terms of oxygen contamination (< 100 ppt), requires continuous circulation of gaseous argon (GAr) and liquid argon (LAr) through adsorption columns filled with solid adsorbents that capture oxygen, nitrogen, and water. This level of purity is especially critical for the LBNF-DUNE project, as even trace amounts of nitrogen and oxygen can significantly affect LAr scintillation light, which is essential for the experiment’s detection process. Notably, scintillation light emission is adversely affected by nitrogen concentrations as low as 1 ppm and oxygen concentrations starting at 0.1 ppm, leading to a reduction in the lifetime and relative amplitude of the slow scintillation component. Meeting these purity requirements presents several engineering challenges in the design of the LAr and GAr purification systems. Three primary challenges are: Integrating the LAr and GAr Flow Systems and Managing Pressure Drop; Heat Transfer in the LAr System; and Filter Design and Adsorbent Selection. Integration of the flow systems must consider the total pressure drop across the pipes and accessories, which is essential for the pump design. The unavailability of commercial pumps capable of handling the head loss and flow rate required for cryogenic fluids complicates this task, as accurately predicting pressure drops is key to specifying suitable pumps. The design of the heat exchangers, particularly condensers, depends on the amount of heat absorbed by the LAr during circulation. Heat transfer management is crucial to prevent vaporization and maintain cryogenic temperatures within the detector and its associated components. Correctly predicting heat transfer and pressure drop ensures the system’s total power consumption remains optimized. Finally, the filtering system’s design must define the number of filters, the mass of adsorbent in each filter, the saturation time, and the number of cycles until saturation. While BASF Cu-0226S and Mol Sieve 4A adsorbents are typically used to capture oxygen and water, nitrogen capture is more complex. Recently, experimental studies in the Liquid Argon Purification Cryostat (PuLArC, ~ 90 L of LAr) at IFGW/Unicamp demonstrated successful nitrogen removal using an innovative Li-FAU Molecular Sieve. These findings were confirmed by similar experiments conducted in the ICEBERG cryostat (~ 3000 L of LAr) at Fermilab, indicating the effectiveness of the Li-FAU adsorbent in purifying LAr from nitrogen. Building on these experimental results, a mathematical model based on mass and energy balances was developed and solved to better understand the adsorption process. The model, incorporating a Pore Diffusion Model (PDM) with parameter optimization, accurately predicted nitrogen concentrations under various operating conditions in the PuLArC and ICEBERG cryostats. This model provides a valuable tool for scaling up the purification process and optimizing system performance for the LBNF-DUNE project. The experiments at ICEBERG confirmed the Li-FAU Molecular Sieve’s capacity to capture nitrogen from LAr, sparking discussions about its potential use in other LAr-based experiments at Fermilab and CERN. This study contributes significantly to the design of the LAr and GAr purification systems for LBNF-DUNE, allowing researchers to predict the time required to reach the desired purity from an initial contamination level and estimate the number of purification cycles before adsorbent saturation.
