IR spectroscopy on liquid hydrogen isotopologues

Future fusion facilities like ITER and DEMO will have huge amounts of tritium and deuterium circulating in their systems as fuel for the fusion plasma. The T2 inventory of first generation power plants will be about 2 to 3 kg, with a throughput of aprox. 1 kg per hour. One important capability of the T2 cycle is to reprocess unburned fuel and to purge tritium and deuterium. For hydrogen isotopologue processing the Isotope Separation System (ISS) is available, applying a cascade of cryogenic distillation columns to enrich the T2. Before reinjecting the tritium back to fusion process, its purity has to be measured without disturbing the distillation process. IR-spectroscopy is being examined as a reliable; reproduceable, fast and non invasive analytic technique for composition analysis of liquid hydrogen mixtures. There are several major challenges on the way to a reliable IR measurement method: On the one hand the hydrogen sample has to be cooled to temperatures of about 20 Kelvin. And on the other hand the IR source and the detector are at room temperature. So enough cooling power and a sufficient thermal insulation are required. But also the analysis of IR spectra is not straight forward due to the overlap of spectral features from the six (H2, HD, D2, HT, DT, T2) hydrogen molecules.