Effect of bremsstrahlung radiation emission on distributions of runaway electrons in magnetized plasmas

TL;DR

This paper investigates how bremsstrahlung radiation influences the distribution and maximum energy of runaway electrons in magnetized plasmas, highlighting its significance relative to synchrotron radiation under various plasma conditions.

Contribution

It provides quantitative analysis and numerical verification of bremsstrahlung effects on electron energy limits and distribution features in tokamak plasmas.

Findings

Bremsstrahlung causes non-monotonic features in electron distributions.

Synchrotron radiation generally dominates over bremsstrahlung in typical tokamak conditions.

High-density scenarios can make bremsstrahlung the dominant radiation loss mechanism.

Abstract

Bremsstrahlung radiation is an important energy loss mechanism for energetic electrons in plasmas. In this paper we investigate the effect of bremsstrahlung radiation reaction on the electron distribution in 2D momentum space. We show that the emission of bremsstrahlung radiation leads to non-monotonic features in the electron distribution function and describe how the simultaneous inclusion of synchrotron and bremsstrahlung radiation losses affects the dynamics of fast electrons. We give quantitative expressions for (1) the maximum electron energy attainable in the presence of bremsstrahlung losses and (2) when bremsstrahlung radiation losses are expected to have a stronger effect than synchrotron losses, and verify these expressions numerically. We find that, in typical tokamak scenarios, synchrotron radiation losses will dominate over bremsstrahlung losses, except in cases of very high density, such as during massive gas injection.