New roles of cavitons in inhomogeneous plasma under strong electromagnetic irradiation

The characteristics of electron plasma waves (EPWs) trapped inside density cavities or cavitons which are generated by the ponderomotive forces associated with the localized waves are experimentally investigated in inhomogeneous, unmagnetized plasmas under strong electro-magnetic (em) excitations. The trapping of EPWs in cavitons is studied in detail by monitoring the wave evolution after the termination of the excitation field in a capacitor-plate experimental configuration. The existence of caviton eigenmodes for the trapped EPWs is confirmed for the first time by using the novel two-frequency excitation technique. Results verify quantitatively the predictions of the Morales-Lee model for resonance absorption. The formation of small-scale cavitons embedded in a large density cavity is observed for the first time during ionospheric heating experiments at the Arecibo Observatory, in which high-power radio waves at frequencies below the maximum electron-plasma frequency of the ionosphere are launched from the ground station in order to modify the ionosphere. This demonstrates the universality of the caviton concept in inhomogeneous plasmas under intense em irradiation