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Electron-acoustic waves (EAWs) as well as electron-acoustic solitary structures play a crucial role in thermalization and acceleration of electron populations in Earth's magnetosphere. These waves are often observed in association with whistler-mode waves, but the detailed mechanism of EAW and whistler wave coupling is not yet revealed. We investigate the excitation mechanism of EAWs and their potential relation to whistler waves using particle-in-cell simulations. Whistler waves are first excited by electrons with a temperature anisotropy perpendicular to the background magnetic field. Electrons trapped by these whistler waves through nonlinear Landau resonance form localized field-aligned beams, which subsequently excite EAWs. By comparing the growth rate of EAWs and the phase mixing rate of trapped electron beams, we obtain the critical condition for EAW excitation, which is consistent with our simulation results across a wide region in parameter space. These results are expected to be useful in the interpretation of concurrent observations of whistler-mode waves and nonlinear solitary structures and may also have important implications for investigation of cross-scale energy transfer in the near-Earth space environment.
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This content will become publicly available on November 28, 2026
Excitation of Whistler‐Mode Waves by an Electron Temperature Anisotropy in a Laboratory Plasma
Abstract Naturally occurring whistler‐mode waves in near‐Earth space play a crucial role in accelerating electrons to relativistic energies and scattering them in pitch angle, driving their precipitation into Earth's atmosphere. Here, we report on the results of a controlled laboratory experiment focusing on the excitation of whistler waves via temperature anisotropy instabilities–the same mechanism responsible for their generation in space. In our experiments, anisotropic energetic electrons, produced by perpendicularly propagating microwaves at the equator of a magnetic mirror, provide the free energy for whistler excitation. The observed whistler waves exhibit a distinct periodic excitation pattern, analogous to naturally occurring whistler emissions in space. Particle‐in‐cell simulations reveal that this periodicity arises from a self‐regulating process: whistler‐induced pitch‐angle scattering rapidly relaxes the electron anisotropy, which subsequently rebuilds due to continuous energy injection and further excites wave. Our results have direct implications for understanding the process and characteristics of whistler emissions in near‐Earth space.
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- Award ID(s):
- 2108582
- PAR ID:
- 10710202
- Publisher / Repository:
- American Geophysical Union (AGU)
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 52
- Issue:
- 22
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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