Association of whistler-wave spectral peak with whistler oscillitons

Determine whether the whistler-wave spectral maximum observed at ω ≈ 0.52 ωe in the particle-in-cell simulation of a core–strahl electron plasma (with oblique propagation and background magnetic field) corresponds to a whistler oscilliton, defined as a whistler-mode structure in which phase and group velocities are equal. Ascertain if the peak’s position is attributable to oscilliton dynamics and clarify its relationship to the lower-frequency prediction from the fluid approach (approximately ω ≈ 0.12 ωe).

Background

In the simulation analyzing the conversion of current-driven Langmuir oscillations into electromagnetic radiation, the authors present frequency spectra of the magnetic field component Bz. Beyond the fundamental and harmonic emissions near the electron plasma frequency, they report electromagnetic activity at whistler-mode frequencies.

The spectrum shows a pronounced maximum at ω ≈ 0.52 ωe, which is substantially higher than the fluid model’s prediction of roughly ω ≈ 0.12 ωe for the whistler wave frequency tied to the mode-coupling point. The authors explicitly state uncertainty about whether this spectral peak is associated with whistler oscillitons, which are characterized by equality of phase and group velocities, referencing earlier work on whistler oscillitons.