Hot-tail runaway electron generation in cooling fusion plasmas

Abstract

Runaway electrons pose a threat to safe operation of magnetic confinement fusion reactors due to the damage they can cause on the reactor wall. During a fast cooling of a fusion plasma, the electric field strength increases and high-energy electrons are accelerated to relativistic speeds, a process called hot-tail runaway generation. To mitigate their effect, reliable and efficient theoretical models to predict generation of hot-tail electrons are of importance. Current numerical methods are computationally expensive and the accuracy of available analytical models has not been found satisfactory. In this work, analytical and simplified numerical models for hot-tail generation including a self-consistent description of the electric field are proposed. The models are benchmarked against numerical simulations and their regions of validity are explored.