A helium isotope separation cryostat with an entropy filter cooled by a G-M cryocooler

Abstract

To obtain ultra-high purity ⁴He, a helium isotope separation cryostat including an entropy filter cooled by a G-M cryocooler was constructed. This cryostat provided possibility for continuous separation of helium isotopes. The entire separation process comprised two stages determined by the state of helium flow through the entropy filter: the startup stage and the steady stage. In this paper, the separation effect under these two stages has been studied, with ³He concentration being tested by Helix SFT™ Mass Spectrometry. The concentration of ³He were $3.31\times {10}^{-8}$,$6.39\times {10}^{-10}$ and $2.41\times {10}^{-10}$ for the feed helium gas, the startup stage and the steady stage. The results indicated that the concentration of ³He separated in the steady stage decreases by two orders of magnitude, and the separation effect of the startup stage is inferior to that of the steady stage. Additionally, a detailed analysis of ³He diffusion and ⁴He superfluid flow is presented, along with potential advancements in helium isotope separation cryostat that could benefit future industrial applications.