Electromagnetic Radiation from Beam-Plasma Instabilities
The mechanism by which unstable electrostatic waves of an electron-beam plasma system are converted into observed electromagnetic waves is of great current interest in space plasma physics. Electromagnetic radiation arises from both natural beam-plasma systems, e.g., type III solar bursts (Papadopoulos, 1979) and kilometric radiation (Maggs, 1978), and from man-made electron beams injected from rockets and spacecraft (Grandal et al., 1980; Winckler et al., 1975; Kawashima, 1980). In spite of numerous laboratory experiments on beam-plasma instabilities, little attention has been paid to electromagnetic wave generation. Only the simplest process, i.e., the conversion of electrostatic to electromagnetic waves in nonuniform plasmas at the critical layer (ω = ωp) is well established in both theory (Piliya, 1966) and experiments (Stenzel et al., 1974). In uniform plasmas it has been theoretically shown (Tsytovitch, 1977) that the scattering of electron plasma waves off ion acoustic waves and other electron plasma waves produces electromagnetic waves near ω ≳ ωpe) and ω ≃ 2ωpe, respectively, where ωpe is the electron plasma frequency. In some three-wave interactions where the electrostatic plasma waves excited by the beam grow to very large amplitudes (eΦ≃ kTe), the normal modes of the system are modified.
KeywordsElectromagnetic Wave Electromagnetic Radiation Plasma Wave Radio Burst Langmuir Probe
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