# Electron parallel closures for arbitrary collisionality

## TL;DR

This paper develops general electron parallel closure models for heat flow, viscosity, and friction in plasmas, valid across all collisionality regimes, simplifying complex calculations for plasma physics applications.

## Contribution

It introduces fitted kernel functions derived from a 6400 moment solution, enabling closure of electron fluid equations without solving higher order moments.

## Key findings

- Fitted kernels match asymptotic behaviors in collisionless limit.
- Closure models applicable to both astrophysical and laboratory plasmas.
- Simplifies plasma modeling by avoiding complex moment equation solutions.

## Abstract

Electron parallel closures for heat flow, viscosity, and friction force are expressed as kernel-weighted integrals of thermodynamic drives, the temperature gradient, relative electron-ion flow velocity, and flow-velocity gradient. Simple, fitted kernel functions are obtained for arbitrary collisionality from the 6400 moment solution and the asymptotic behavior in the collisionless limit. The fitted kernels circumvent having to solve higher order moment equations in order to close the electron fluid equations. For this reason, the electron parallel closures provide a useful and general tool for theoretical and computational models of astrophysical and laboratory plasmas.