A fluid-kinetic framework for self-consistent runaway-electron simulations

TL;DR

This paper introduces a fluid-kinetic framework that self-consistently models runaway-electron physics by coupling kinetic and macroscopic plasma evolution, using a probabilistic closure to distinguish bulk and tail populations.

Contribution

It presents a novel approach to self-consistently couple kinetic runaway-electron physics with plasma evolution through a probabilistic closure and a division into bulk and tail populations.

Findings

Derived macroscopic one-fluid equations with source and sink terms.

Established a probabilistic closure preserving non-negative distributions.

Formulated a kinetic equation for runaway-electron populations.

Abstract

The problem of self-consistently coupling kinetic runaway-electron physics to the macroscopic evolution of the plasma is addressed by dividing the electron population into a bulk and a tail. A probabilistic closure is adopted to determine the coupling between the bulk and the tail populations, preserving them both as genuine, non-negative distribution functions. Macroscopic one-fluid equations and the kinetic equation for the runaway-electron population are then derived, now displaying sink and source terms due to transfer of electrons between the bulk and the tail.