Neoclassical Pitch-Angle Scattering of Runaway Electrons

TL;DR

This paper reveals that tokamak magnetic geometry causes a neoclassical pitch-angle scattering effect on runaway electrons, surpassing collisional scattering and affecting their energy limits, which challenges existing gyro-center models.

Contribution

It introduces the concept of neoclassical pitch-angle scattering in runaway electrons and shows its significant impact on their energy limits and modeling.

Findings

Neoclassical scattering dominates over collisional scattering.

Energy limits of runaway electrons are higher than previously predicted.

Runaway electron behavior depends heavily on magnetic field configuration.

Abstract

It is discovered that the tokamak field geometry generates a pitch-angle scattering effect for runaway electrons. This neoclassical pitch-angle scattering is much stronger than the collisional scattering and invalidates the gyro-center model for runaway electrons. As a result, the energy limit of runaway electrons is found to be larger than the prediction of the gyro-center model and to depend heavily on the background magnetic field.