Resonant excitation of whistler waves by a helical electron beam

TL;DR

This study demonstrates the excitation of chorus-like whistler waves in a laboratory plasma using a helical electron beam, revealing the underlying resonance mechanisms and their implications for Earth's magnetosphere.

Contribution

It provides the first experimental observation of resonant excitation of whistler waves by a helical electron beam and identifies the specific resonance processes involved.

Findings

Whistler waves are excited via Landau, cyclotron, and anomalous cyclotron resonances.

The dominant mode is quasi-parallel, while oblique modes are excited through Landau and anomalous cyclotron resonances.

Linear wave growth rates align with experimental observations.

Abstract

Chorus-like whistler-mode waves that are known to play a fundamental role in driving radiation-belt dynamics are excited on the Large Plasma Device by the injection of a helical electron beam into a cold plasma. The mode structure of the excited whistler wave is identified using a phase-correlation technique showing that the waves are excited through a combination of Landau resonance, cyclotron resonance and anomalous cyclotron resonance. The dominant wave mode excited through cyclotron resonance is quasi-parallel propagating, whereas wave modes excited through Landau resonance and anomalous cyclotron resonance propagate at oblique angles that are close to the resonance cone. An analysis of the linear wave growth rates captures the major observations in the experiment. The results have important implications for the generation process of whistler waves in the Earth's inner magnetosphere.