Nonlinear interactions of focused resonance cone fields with plasmas

Abstract

A simple yet novel rf exciter structure has been developed for generating remotely intense rf fields in a magnetoplasma. It is a circular line source of radius R in a plane ⊥B0 driven with an rf signal at ω <ωc≃ωp (where ωc, ωp are the electron cyclotron and electron plasma frequency, respectively) which excites two resonance cones with focal points at z=±R cotΘc (Θc is the cone angle). The rf intensity increases away from the exciter to reach a maximum (approximately 20 dB enhancement) at the remote focal points. This arrangement is ideally suited to study nonlinear interactions free of boundary effects. At large applied rf signals, ε0Erf2/nkTe≳0.2, a strong density depression in the focal region (δn/n≳40%) is observed. The density perturbation modifies the cone angle and field distribution. This nonlinear interaction leads to a rapid growth of ion acoustic wave turbulence and a corresponding random rf field distribution in a broadened focal region. The development of the interaction is mapped in space and time.