Design of a Cryostat for Spectroscopic Investigation of All Hydrogen Isotopologues in the Solid, Liquid, and Gaseous Phases

A crucial part of the closed fuel cycle of future fusion power plants will be isotope separation, which takes place in a cryogenic distillation refraction column, where all six hydrogen isotopologues are separated due to their different vapor pressures at a given temperature. For monitoring and process controlling, the Tritium Laboratory Karlsruhe has investigated liquid hydrogen by infrared (IR) absorption spectroscopy and presented the first successful calibration for the inactive isotopologues. Now, the new Tritium Absorption InfraRed Spectroscopy 2 (T₂ApIR) experiment, which is fully tritium compatible, is under construction and aims to provide a calibration for concentration measurements of all six hydrogen isotopologues in solid, liquid, and gaseous phases via not only IR absorption but also Raman spectroscopy. One major challenge of the new experiment so far has been the design of the cryostat, which had to fulfill diverse technical and safety requirements regarding tritium compatibility, cryogenics, and overpressure and the combination of optical components for Raman and IR spectroscopy.