Fast dynamics of radiofrequency emission in plasmas with runaway electrons

TL;DR

This study measures high-resolution radiofrequency emissions from plasmas with runaway electrons, revealing rapid bursts linked to kinetic instabilities and providing insights into RE dynamics and wave coupling phenomena.

Contribution

It presents unprecedented high-resolution measurements of RF emissions in plasmas with runaway electrons, uncovering rapid bursts and nonlinear wave interactions affecting RE evolution.

Findings

Radiofrequency bursts correlate with enhanced RE pitch angle scattering.

Spectral broadening indicates nonlinear wave coupling during emission growth.

RF emission ceases at RE plateau onset and reappears as intense bursts.

Abstract

Radiofrequency emission in the 0.4 - 3 GHz range from FTU plasmas in presence of runaway electrons (RE) has been measured with unprecedentedly high time resolution. Rapid emission bursts associated with enhanced RE pitch angle scattering reveal kinetic instabilities affecting evolution of the RE population from the buildup phase. Such measurements also provide a sensitive monitor for instabilities during early RE formation. The leading edge of radio bursts is much shorter than interleaving periods of low emission; spectral broadening during growth indicates nonlinear wave coupling as an explanation for the observed intermittency. Radiofrequency emission disappears at the beginning of post-disruption RE plateaus, and subsequently reappears in the shape of very intense bursts accompanied by strong rises of suprathermal electron cyclotron emission.