Cryostat Cooling R&D for nEXO

The search for neutrinoless double-beta decay probes new physics of the unknown neutrino mass discovered by oscillation experiments. The nEXO experiment is planned to have a half-life sensitivity of 10²⁸ years, covering the inverted mass hierarchy for mediation by light Majorana neutrinos. nEXO utilizes 5 tons of xenon enriched in isotope 136 arranged in a liquid time projection chamber immersed in an HFE thermal bath. The cryogenic cooling is planned via active recirculation of the HFE to an external heat exchanger. This project considers an alternative temperature setpoint maintenance strategy using thermosyphons to cool directly the HFE and motivated by the experience of the EXO-200 experiment and the approach of large liquid xenon dark matter experiments. Experience with operation of an R&D thermosyphon system and plans for HFE cooling tests are discussed.