A review of cyclotron harmonic phenomena in plasmas

In recent years, cyclotron harmonic phenomena have been encountered in many branches of plasma physics. For example, anomalously high noise radiation near the electron and ion cyclotron harmonic frequencies (nωce, nωci) has been observed from plasmas used in thermonuclear fusion studies. Transmission resonances near (nωce) have been detected in the laboratory in perpendicular propagation experiments, while satellite explorations have established the existence of ionospheric resonance effects near these frequencies. The substantial volume of experimental data accumulated on cyclotron harmonic phenomena can be interpreted qualitatively, and in some cases quantitatively, in terms of cyclotron harmonic waves whose propagation has been predicted for warm plasmas in a magnetic field. The review gives a brief outline of the theory, and concentrates on the basic physical mechanisms of the effects observed experimentally. These phenomena are of considerable practical importance in the understanding of processes occurring in fusion study devices, other laboratory discharges, and the ionosphere. There are several potential applications to plasma diagnostics; the paper concludes with a brief discussion of them.