Efficiency of caviton formation as a function of plasma density gradient

Abstract

The effect of a zeroth-order density gradient on the development of cavitons has been investigated experimentally and numerically. The cavitons were produced via excitation of electron plasma waves (EPW) with a modest (E2/4πnTe≪1) resonant radio-frequency pump. The location of the resonance, on an inverse-parabolic density profile, was varied, with all other parameters being held constant. The depth of the caviton, and the strength of its associated trapped electric fields, are found to depend strongly on the density gradient scale length at the critical layer, with a maximum occurring when this length is infinite, at the flat top of the density profile. The results are accounted for by the dependence on the density gradient of the EPW convection rate and wave-breaking time. The study helps illuminate recent large-scale ionospheric density modification experiments.