Boltzmann Analysis of Cryogenic $\text{He}$ –$\text{H}_{\text{2}}$ Gas Mixtures as Dielectric Media for High-Temperature Superconducting Power Devices

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Analysis of the dielectric properties of gas mixtures in the context of their application as cryogens for high-temperature superconducting power applications is presented. Boltzmann analysis was conducted for pure gaseous helium (He) and its mixtures consisting of small mole fractions of gaseous hydrogen (H 2 ) to establish a theoretical foundation for the observed enhancement in dielectric strength at cryogenic temperatures. Boltzmann analysis showed that the electron energy distribution function shifts to the lower energy region, the reduced ionization coefficient (α/N), and the reduced effective ionization coefficient ((α - η)/N) decreases, whereas the reduced attachment coefficient (η/N) and the reduced critical electric field ((E/N)cr) increases as the mole fractions of H 2 increase in the He-H 2 mixture. The results of the analysis predict a persisting enhancement of dielectric strength by adding larger amounts of H 2 beyond the reported 4 mol% in the He-H 2 mixtures. The analysis also provides a basis for identifying a suitable gas mixture for gaseous cryogen cooled superconducting device with a required power rating.