Observation of whistler wave instability driven by temperature anisotropy of energetic electrons on EXL-50 spherical torus

TL;DR

This paper reports the first observation of whistler wave instability driven by energetic electron temperature anisotropy in a spherical torus, with implications for wave-particle interactions and runaway electron control in fusion devices.

Contribution

It presents the first experimental detection of whistler waves driven by electron anisotropy in a spherical torus plasma.

Findings

Electromagnetic modes observed in 30-120MHz range.

Modes match dispersion relation of whistler waves.

Suppression of whistler waves by combined LHW and ECW.

Abstract

Electromagnetic modes in the frequency range of 30-120MHz were observed in electron cyclotron wave (ECW) steady state plasmas on the ENN XuanLong-50 (EXL-50) spherical torus. These modes were found to have multiple bands of frequencies proportional to the Alfv\'en velocity. This indicates that the observed mode frequencies satisfy the dispersion relation of whistler waves. In addition, suppression of the whistler waves by the synergistic effect of Lower Hybrid Wave (LHW) and ECW was also observed. This suggests that the whistler waves were driven by temperature anisotropy of energetic electrons. These are the first such observations (not runaway discharge) made in magnetically confined toroidal plasmas and may have important implications for studying wave-particle interactions, RF wave current driver, and runaway electron control in future fusion devices.