Nonlinear Generation of Electromagnetic Waves through Induced Scattering by Thermal Plasma.

E. M. Tejero,D. D. Blackwell,C. Crabtree,W. E. Amatucci,G. Ganguli,L. Rudakov,M. Mithaiwala

doi:10.1038/srep17852

E. M. Tejero, D. D. Blackwell + Show 5 more

Open Access

https://doi.org/10.1038/srep17852

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Abstract

We demonstrate the conversion of electrostatic pump waves into electromagnetic waves through nonlinear induced scattering by thermal particles in a laboratory plasma. Electrostatic waves in the whistler branch are launched that propagate near the resonance cone. When the amplitude exceeds a threshold ~5 × 10−6 times the background magnetic field, wave power is scattered below the pump frequency with wave normal angles (~59°), where the scattered wavelength reaches the limits of the plasma column. The scattered wave has a perpendicular wavelength that is an order of magnitude larger than the pump wave and longer than the electron skin depth. The amplitude threshold, scattered frequency spectrum, and scattered wave normal angles are in good agreement with theory. The results may affect the analysis and interpretation of space observations and lead to a comprehensive understanding of the nature of the Earth’s plasma environment.

Highlights

Generalization of the electrostatic theory of induced nonlinear scattering of lower hybrid waves[5] to include the electromagnetic effects[6] showed that electrostatic waves in the intermediate frequency range, Ω i < ω < Ω e (Ω i,e are the ion and electron gyrofrequencies), with a large wave normal angle may be scattered by a resonant nonlinear interaction with thermal electrons into electromagnetic waves with smaller wave normal angles[6,7]
(3) The beat wave that would be present between the pump and scattered waves is in Landau resonance with the background thermal electrons 2πΔ f/(vteΔ kz) ~ 1, where vte is the electron thermal speed and Δ kz is the absolute value of the difference between the parallel wave vectors of the pump and scattered
The perpendicular wavelength of the scattered waves is an order of magnitude larger than that of the pump wave and longer than the electron skin depth

Summary

Introduction

Generalization of the electrostatic theory of induced nonlinear scattering of lower hybrid waves[5] to include the electromagnetic effects[6] showed that electrostatic waves in the intermediate frequency range, Ω i < ω < Ω e (Ω i,e are the ion and electron gyrofrequencies), with a large wave normal angle may be scattered by a resonant nonlinear interaction with thermal electrons into electromagnetic waves with smaller wave normal angles[6,7]. (1) Given sufficient amplitude of a pump wave with frequency fpump and k⊥>1, a new spectral feature, the scattered wave, is observed at a downshifted frequency fpump − Δ f and k⊥

Results

Conclusion