Electro-diffusion in a plasma with two ion species

TL;DR

This paper investigates electro-diffusion in multicomponent plasmas, revealing its dependence on ion charge-to-mass ratios and its role in fuel ion separation in inertial confinement fusion, with explicit formulas and comparative analysis.

Contribution

It provides an explicit expression for electro-diffusion ratios and analyzes its impact relative to baro-diffusion in different ion mixtures.

Findings

Electro-diffusion vanishes when ion species have identical charge-to-mass ratios.

Electro-diffusion enhances baro-diffusion in D-T mix.

Electro-diffusion cancels baro-diffusion in D-3He mix.

Abstract

Electric field is a thermodynamic force that can drive collisional inter-ion-species transport in a multicomponent plasma. In an inertial confinement fusion (ICF) capsule, such transport causes fuel ion separation even with a target initially prepared to have equal number densities for the two fuel ion species. Unlike the baro-diffusion driven by ion pressure gradient and the thermo-diffusion driven by ion and electron temperature gradients, electro-diffusion has a critical dependence on the charge-to-mass ratio of the ion species. Specifically, it is shown here that electro-diffusion vanishes if the ion species have the same charge-to-mass ratio. An explicit expression for the electro-diffusion ratio is obtained and used to investigate the relative importance of electro- and baro-diffusion mechanisms. In particular, it is found that electro-diffusion reinforces baro-diffusion in the deuterium and tritium mix, but tends to cancel it in the deuterium and helium-3 mix.