Hybrid 3He enrichment by coupling entropy filtration with Sub-1K vapor-phase extraction

Helium-3 is a scarce isotope essential for neutron detection, dilution refrigeration, and other cryogenic technologies, motivating compact and efficient methods for 3 He enrichment and recovery. Here we demonstrate a hybrid cryogenic separation method that couples entropy filtration with sub-1 K vapor-phase extraction. In the high-recovery mode, superfluid 4 He is selectively transported through an entropy filter while 3 He is retained on the enriched side. For a feed gas containing 6.3% 3 He, the product mole fraction reaches 30.1%, while the 4 He-rich side contains only 0.046% 3 He, corresponding to a ³He recovery efficiency of approximately 99%. To exceed the enrichment limit of entropy filtration alone, the same platform is operated in a high-enrichment mode, where 3 He-rich vapor is selectively withdrawn below 1 K. This mode increases the 3 He mole fraction from 0.5% to 28.1% and from 6.3% to 76.8%. The enhanced performance arises from a coupled liquid- and vapor-phase separation mechanism: entropy filtration continuously removes 4 He from the liquid phase, whereas the much higher vapor pressure of 3 He below 1 K enriches the extracted vapor. This proof-of-concept study establishes a practical route toward high-recovery and high-enrichment 3 He separation in a compact cryogenic platform.