Four-Fluid Axisymmetric Plasma Equilibrium Model Including Relativistic Electrons and Computational Method and Results

TL;DR

This paper develops a relativistic four-fluid plasma equilibrium model including energetic electrons, providing new computational methods and applying them to observed and hypothetical high-temperature plasma scenarios.

Contribution

It introduces a relativistic multi-fluid equilibrium formulation with a novel axial angular momentum approach and applies it to complex plasma configurations.

Findings

Relativistic effects significantly influence plasma equilibrium at high electron temperatures.

The model successfully describes observed spherical torus plasma with energetic electrons.

Higher electron temperatures reveal notable relativistic modifications in plasma behavior.

Abstract

A non-relativistic multi-fluid plasma axisymmetric equilibrium model was developed recently to account for the presence of an energetic electron fluid in addition to thermal electron and ion fluids. The equilibrium formulation of a multi-fluid plasma with relativistic energetic electrons is developed and reported in this paper. Relativistic effects in a fluid model approximation can appear in two ways: due to a large macroscopic fluid velocity comparable to the speed of light and large particle's microscopic random motion which becomes significant if the temperature becomes comparable to or larger than the electron rest mass-energy. It is found that the axial component of relativistic generalized angular momentum can be used to describe relativistic axisymmetric equilibrium. The formulation is applied to a four-fluid plasma composed of a relativistic energetic electron fluid, a thermal electron fluid, and fluids of two thermal ion species (e.g. proton and boron ions). The four-fluid density expression which is consistent with the electrostatic potential is obtained and applied in the computation. An example equilibrium approximating a four-fluid plasma recently observed in a solenoid-free ECRH sustained spherical torus plasma is calculated and presented. A second equilibrium that extends the energetic electron temperature of the first example to 679keV is calculated revealing significant relativistic effects.