Multistage Sub-Kelvin Distillation of 3He–4He Mixtures for Ultra-High-Purity 3He Production

Helium-3 ( 3 He) is an important cryogenic resource for scientific and industrial applications, and helium isotope separation remains one of the key technical challenges in the production of high-purity 3 He. We report an integrated sub-kelvin distillation platform for the enrichment of 3 He from 3 He- 4 He mixtures over a wide range of feed-gas abundance. Distillation experiments were performed using feed gases containing 3.7% and 20.0% 3 He. The system achieved a minimum operating temperature of 447 mK. For the feed gas with a 3 He abundance of 20.0%, the maximum 3 He isotopic abundance reached 94.1% after the first-stage distillation, while a 3 He recovery rate exceeding 90% was achieved at a product abundance of 88.2%. Second- and third-stage distillations further increased the 3 He isotopic abundance to above 99.5% and 99.9955 ± 0.0016%, respectively, with a total recovery rate exceeding 85%. These results demonstrate that sub-kelvin multistage distillation provides an efficient route for upgrading intermediate-abundance 3 He- 4 He mixtures to ultra-high-purity 3 He and provides critical experimental guidance and engineering support for the optimization of helium isotope separation processes.