Conversion of Electrostatic Plasma Waves into Electromagnetic Waves: Numerical Calculation of the Dispersion Relation for All Wavelengths

Abstract

The dispersion curves have been computed for a wide range of wavelengths from electromagnetic waves to electrostatic waves in a magnetoactive warm plasma with a Maxwellian velocity distribution function. The computation was carried out mainly for the perpendicular propagation mode. The upper hybrid resonance is the connection point of the electrostatic waves and the electromagnetic waves. The electrostatic waves not associated with the upper hybrid resonance are subjected to electron cyclotron damping when the wavelength becomes long. Oblique propagation is allowed for the electrostatic waves in a frequency range from the plasma frequency to the upper hybrid resonance frequency in the long‐wavelength region where Landau damping can be neglected and where the electrostatic mode smoothly connects to the electromagnetic X‐mode. In a slightly inhomogeneous plasma, the Bernstein‐mode electrostatic wave can escape by being converted into the O‐mode electromagnetic wave; two reflections take place during this escape process. The frequency range of the escape coincides with the Cerenkov radiation of the electromagnetic waves, but these two mechanisms indicate clear contrast in its origin. The electromagnetic Cerenkov radiation is produced interacting with the high‐energy plasma beam with velocity range l00υth < υ < l000υth (for the nonrelativisitic plasma), where υth is the electron thermal velocity, whereas the origin of the electrostatic waves is in the interaction with the low‐energy plasma beam.