Physics of Thermal Cavitons

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Physics of thermal cavitons has been investigated experimentally and theoretically in this research project.The ionosphere can be considered a natural plasma laboratory of great size with no boundaries and an execllent plasma confinement. During ionospheric modification experiments with "long-time, high-power high-frequency (HF) radio wave heating, large-scale (over a few tens of" kilometers) density depletions (nearly 50% density modification) have been observed. Basic processes of this phenomenon can be understood in terms of the Ohmic heating of the plasma "near the HF reflection layer and the subsequent plasma expulsion from this layer. As a result, " these density depletions are dubbed 'thermal cavitons'.The results of recent ionospheric modification experiments performed at Arecibo, Puerto Rico, have revealed that 1)the increase in the electron temperature near the HF reflection layer is "roughly 5 times the initial one, 2) radar observations suggest the existence of strong ion" "turbulence inside thermal cavitons, and 3) thermal cavitons can interact with naturally" generated density bubbles.The size of a thermal caviton sometimes appears too large for the electromagnetic energy "injected into the ionosphere. In order to solve this problem, a new transport model has been" "introduced, in which the self-focusing of the injected em wave due to an initial weak density" cavity in a background plasma is phonomenologically imposed. Numerical analysis of the model equations appear to indicate that we are on the right track.Some laboratory experiments have been performed to investigate the effects of short-time scale plasma turbulence on thermal cavitons.