Generalized Impurity Pinch in Partially Magnetized Multi-Ion Plasma

TL;DR

This paper extends the understanding of impurity pinch effects in multi-ion plasmas to partially magnetized regimes, showing that equilibrium ion densities depend on external forces regardless of ion magnetization, with implications for laboratory plasma experiments.

Contribution

It generalizes pinch relations to partially magnetized plasmas, clarifying the roles of collisional and Larmor magnetization in multi-ion transport.

Findings

Ion density profiles depend on external forces regardless of ion magnetization.

Impurity transport can be observed and manipulated in MagLIF experiments.

Extended models apply to a broader range of plasma conditions.

Abstract

In a two-ion-species plasma with disparate ion masses, heavy ions tend to concentrate in the low-temperature region of collisionally magnetized plasma and in the high-temperature region of collisionally unmagnetized plasma, respectively. Moreover, collisional magnetization can be determined as the ratio of the light ion gyrofrequency to the collision frequency of light and heavy ion species, and the behavior of this effect in the intermediate regime of partially magnetized plasma is predominantly dependent on this Hall parameter. Multi-ion cross-field transport has been described before in the collisionally magnetized plasma regime, and generalized pinch relations, which describe densities of ion species in equilibrium in that plasma, are found in the literature. In this paper, the role of collisional magnetization and Larmor magnetization in multi-ion collisional transport is clarified and generalized pinch relations are extended to the partially magnetized regime, in which the ion Hall parameter may be small, as long as electrons remain collisionally magnetized. Equilibrium ion density profiles have the same dependence on external forces and on each other regardless of collisional magnetization of ions. The expansion of the range of validity of multi-ion collisional transport models makes them applicable to a wider range of laboratory plasma conditions. In particular, ion density profiles evolve sufficiently fast for radial impurity transport to be observable around stagnation on MagLIF, leading to expulsion of heavy ion impurities from the hotspot as long as plasma becomes sufficiently collisionally magnetized during the implosion.