Effect of temperature and heat input on helium isotope separation driven by an entropy filter

Abstract

To understand the effect of temperature and heat input on helium isotope separation driven by an entropy filter, the thermomechanical flow of superfluid helium through an entropy filter for obtaining high purity ⁴He is experimentally investigated. For this method, there are two important indicators: separation flow (flow rate) and separation effect (³He concentration). The separation flow rate is examined at various temperatures ranging from 1.6 K to 1.9 K of feed helium. Different heat inputs (Q) are applied to the entropy filter outlet to drive superfluid ⁴He flowing through the porous element. The results demonstrate that the flow rate increases as the feed helium temperature decreases and heat input increases. Simultaneously, ³He diffusion is detected as the superfluid helium passes through the entropy filter. The concentration of ³He, filtered at different temperature ranging from 1.6 K to 1.9 K, are analyzed using HELIX SFT Static Vacuum Mass Spectrometer. The findings reveal that the ³He concentration decreases with an increase in the temperature of the feed helium bath. ³He concentration of feed helium is around $3.3\times {10}^{-8}$. Specifically, the ³He concentration in the filtered helium at 1.6 K is approximately $3.2\times {10}^{-10}$, while at 1.9 K, it reduced to $2.2\times {10}^{-10}$. This suggests that ³He diffusion in He II is inversely proportional to the He II temperature from 1.6 K to 1.9 K, resulting in a lower ³He concentration at higher temperatures.