Electron Tail Suppression and Effective Collisionality due to Synchrotron Emission and Absorption in Mildly Relativistic Plasmas

TL;DR

This paper develops a self-consistent model for synchrotron radiation effects in mildly relativistic plasmas, revealing significant suppression of high-energy electron tails and reduced radiation emission compared to classical assumptions.

Contribution

It introduces a novel Fokker-Planck operator incorporating a blackbody synchrotron diffusion model for accurate plasma radiation analysis.

Findings

Electron tail suppression due to synchrotron effects

Reduced radiation emission in relativistic electron populations

Enhanced understanding of energy distribution in fusion plasmas

Abstract

Synchrotron radiation losses are a significant cause of concern for high-temperature aneutronic fusion reactions such as proton-Boron 11. The fact that radiation losses occur primarily in the high-energy tail, where the radiation itself has a substantial impact on the electron distribution, necessitates a self-consistent approach to modeling the diffusion and drag induced by synchrotron absorption and emission. Furthermore, an accurate model must account for the fact that the radiation emission spectrum is momentum-dependent, and the plasma opacity is frequency-dependent. Here, we present a simple Fokker-Planck operator, built on a newly-solved-for blackbody synchrotron diffusion operator, which captures all relevant features of the synchrotron radiation. Focusing on magnetic mirror fusion plasmas, we show that significant suppression of the electron distribution occurs for relativistic values of the perpendicular electron momentum, which therefore emit much less radiation than predicted under the assumption of a Maxwell-Juttner distribution.