Electromagnetic Wave Interactions with Inhomogeneous Plasmas
Experimental observations of electromagnetic wave propagation and interactions with a large inhomogeneous laboratory plasma are summarized. The dominant process is the conversion of electromagnetic waves into electrostatic waves whose field strengths are enhanced by several orders of magnitude in the vicinity of the resonant layer where the incident frequency matches the local plasma frequency. Strong local accelerations of electrons and ions by these localized resonant fields are described. Density cavities produced by the digging actions of these ponderomotive forces are called “cavitons” which coexist with the rf fields. Parametric decay instabilities are found to be a much weaker process compared with the caviton formation at the resonant layer. A double resonance technique of controlling ion dynamics at a specific location in an inhomogeneous plasma is demonstrated. The correlations between the present experiments and laser-plasma interactions, as well as radio wave interactions with the ionosphere, are discussed.
KeywordsDensity Perturbation Langmuir Probe Ponderomotive Force Critical Layer Inhomogeneous Plasma
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