Cross-field resonance effects near the f q2 frequency

Abstract

The cross-field radiation from a point source in a warm magnetoplasma is studied near the fq2 frequency where the group velocity of cross-field waves vanishes, between the upper hybrid frequency or the second electron gyroharmonic, whichever is the higher, and the third gyroharmonic. Calculations are made of the electrostatic wave potential created by an alternating point charge in a Maxwellian magnetoplasma, neglecting collisions and forced ion motion. The integral which gives the potential is evaluated both analytically and numerically by using the least-damped-root approximation which involves considering only three roots of the dispersion equation for electrostatic waves. The good agreement between the approximate analytical and the exact numerical calculations in a cross-field direction permits one to understand physically the behavior of the three-wave interference pattern which depends on the excitation frequency, the distance of observation, and the electron density and temperature. Two new theoretical effects are primarily studied: (i) the potential becomes infinite at fq2 when collisions are neglected, and (ii) an oscillatory structure can occur at frequencies less than fq2. The main characteristics of these effects are derived as functions of the plasma parameters. In particular, it is found that the fq2 resonance arises with extremely sharp outlines and neatly differentiates between two frequency ranges with quite different potential patterns. Finally, the possibility of observing these resonance effects in the laboratory and by space experiments is discussed.