Electron kinetics inferred from observations of microwave bursts during edge localised modes in the Mega-Amp Spherical Tokamak

TL;DR

This paper investigates electron behavior during ELMs in a tokamak, revealing that the anomalous Doppler instability explains observed microwave emissions and electron acceleration phenomena.

Contribution

It introduces the role of the anomalous Doppler instability in electron kinetics during ELMs, highlighting effects not captured by standard fluid models.

Findings

Electron acceleration parallel to magnetic field observed during ELMs

Rapid perpendicular momentum acquisition explained by anomalous Doppler instability

Microwave emissions linked to collective radiative relaxation processes

Abstract

Recent measurements of microwave and X-ray emission during edge localised mode (ELM) activity in tokamak plasmas provide a fresh perspective on ELM physics. It is evident that electron kinetics, which are not incorporated in standard (fluid) models for the instability that drives ELMs, play a key role in the new observations. These effects should be included in future models for ELMs and the ELM cycle. The observed radiative effects paradoxically imply acceleration of electrons parallel to the magnetic field combined with rapid acquisition of perpendicular momentum. It is shown that this paradox can be resolved by the action of the anomalous Doppler instability which enables fast collective radiative relaxation, in the perpendicular direction, of electrons accelerated in the parallel direction by inductive electric fields generated by the initial ELM instability.