Demonstration of the feasibility of the D/T-mixture selective pumping in fusion reactors using superpermeable membranes

The niobium superpermeable membrane (SPM) in the shape of thin-walled tube with an area of 600 m$^2$ was coupled with incandesced tantalum ribbons purposed for thermal dissociation of H$_2$ molecules. The SPM had resistive heating, which made it possible to carry out its high-temperature treatment. This was used to in-situ sulfidate the SPM input surface through H$_2$S pyrolysis in order to form an effective energy barrier against the recombinative re-emission of absorbed hydrogen atoms and thereby drastically improve the SPM performance. Permeation experiment was carried out in the H$_2$ pressure range relevant to divertor operation (Н$_2$ 6 $\cdot$ 10$^{-4}$–1 $\cdot$ 10$^{-2}$ Torr.). A high efficiency of atomic hydrogen utilization was demonstrated: the SPM pumping speed was 480 l/s whereas the speed of H$_2$ molecule dissociation with tantalum ribbons did not exceed 880 l/s. The SPM pumping speed remained as high as 440 l/s when compression ratio reached 400. The permeation flux density achieved $\sim$10$^{21}$Н$_2$/(m$^2$ $\cdot$ s) at the total SPM throughput of $\sim$6 $\cdot$ 10$^{19}$ Н$_2$/s. The hydrogen pumped out and pre-compressed by the SPM was eventually compressed to normal pressure directly by the foreline pump without any intermediate steps.