核融合研究

The purpose of this-paper is to investigate theoretically the scattering characteristics of electromagnetic waves by a cylindrically inhomogeneous irregularity in an unmagnetized plasma at oblique incidence. This problem is very important in radio wave propagation in the ionosphere.
In a homogeneous plasma embedded a cylindrical irregularity whose radial density distribution is assumed to be of parabolic form. Under this condition, analytical expressions of scattered wave fields produced by radio waves at any angle with the irregularity are discussed. Also the wave field die tributions inside the irregularity are fully given. Formulas of scattering patterns are given analytically as a function of frequency, incidence angle and irregularity width. As special cases, the scattering by a magnetic field-aligned irregularity at normal incidence and by irregularities with regular spatial distribution are also discussed.

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Characteristics of hot electron plasmas produced by beamplasma discharge are investigated both experimentally and theoretically. The experimental results on excited waves, selfsustained conditions, hot electron production mechanism and diffusion precess of charged particles are compared with the theoretical predictions. Ion plasma waves are found to be excited in such a plasma due to a coupling with slow cyclotron waves of the electron beam. Electron hybrid wave interaction with beam slow waves becomes essential in its burnout state. Self-sustained conditions of this discharge are determined in its parameter space. Production mechanism of hot electrons is examined from energy measurement of radiated X-ray, which gives a possible evidence of eiectron cyclotron heating in this RF discharge. Diffusion of charged particles (cold electrons) obeys ambiolar theory in quiescent plasma state, but in turbulent plasmas diffusion tends to occur with large diffusion coefficient beyond clasicas values, which is presumably due to anomalous enhancement of apparent collision frequencies.

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