Physics of runaway electrons in tokamaks

Abstract

Of all electrons, runaway electrons have long been recognized in the fusion community as a distinctive population. They now attract special attention as a part of ITER mission considerations. This review covers basic physics ingredients of the runaway phenomenon and the ongoing eorts (experimental and theoretical) aimed at runaway electron taming in the next generation tokamaks. We emphasize the prevailing physics themes of the last 20 years: the hot-tail mechanism of runaway production, runaway electron interaction with impurity ions, the role of synchrotron radiation in runaway kinetics, runaway electron transport in presence of magnetic fluctuations, micro-instabilities driven by runaway electrons in magnetized plasmas, and vertical stability of the plasma with runaway electrons. The review also discusses the implications of the runaway phenomenon for ITER and the current strategy of runaway electron mitigation.