Microwave Scattering and Noise Emission from Afterglow Plasmas in a Magnetic Field

Abstract

The microwave reflection and noise emission (extraordinary mode) from cylindrical rare‐gas (He, Ne, Ar) afterglow plasmas in an axial magnetic field is described. Reflection and noise emission are measured as a function of magnetic field near electron cyclotron resonance (ω ≈ ω꜀) with electron density as a parameter (ωₚ < ω). A broad peak, which shifts to lower values of ω꜀/ω) as electron density increases, is observed for (ω꜀/ω) ≤ 1. For all values of electron density a second sharp peak is found very close to cyclotron resonance in reflection measurements. This peak does not occur in the emission data. Calculations of reflection and emission using a theoretical model consisting of a one‐dimensional, cold plasma slab with nonuniform electron density yield results in qualitative agreement with the observations. Both the experimental and theoretical results suggest that the broad, density‐dependent peak involves resonance effects at the upper hybrid frequency ((ωₕ² = (ω꜀² + (ωₚ²) of the plasma.

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