Design Studies For The LATTE Test Stand

The Large Enriched Germanium Experiment for Neutrinoless Double-Beta Decay (LEGEND) is an international collaboration searching for a rare, theorized process called neutrinoless double beta decay (0νββ), which could provide important insights into the matter-antimatter asymmetry of the universe. The Liquid Argon Test Tank with Extensibility (LATTE) is a cryogenic prototype system at the University of North Carolina at Chapel Hill designed to support detector R&D for the next phase of the experiment, LEGEND-1000. The test stand consists of approximately 300~L liquid argon (LAr) cryostat equipped with high-purity germanium detectors.          This thesis presents two technical studies informing the design of the LATTE test stand. Finite element analysis in Autodesk Fusion 360 is used to model steady-state and transient heat loads across the primary thermal pathways in the cryostat. The results indicate that approximately 83 W of cooling power is required for stable operation, corresponding to a steady-state LAr boil-off rate of 0.32 L/s. Among transient operation scenarios, the detector deployment process produces the maximum heat load of 568 W with a boil-off rate of 2.16 L/s, while the initial LAr fill produces a heat load of 138 W with a boil-off rate of 0.52 L/s. These estimates directly inform the re-condensation system design and argon handling procedures required to maintain LAr purity for appropriate experimental testing. Geant4 simulations of the LATTE detector geometry are used to optimize placement of the calibration source deployment tube, balancing detection efficiency against dead time from pileup. An optimal source tube placement of 160-210 mm from the detector string center is determined, achieving a pileup probability of 15-20% for {Th}{228} while keeping calibration run durations practical given available specific source activities. Together, these results provide concrete design constraints and operational parameters for LATTE in direct support of LEGEND-1000.