Perpendicular distribution of electrostatic electron-cyclotron radiation under dense plasma conditions

The electrostatic potential distribution of a point source antenna is studied numerically within the first dispersion branch defined by 1<Ω<2, where Ω is the monochromatic frequency of the source normalized to the electron gyrofrequency. The whole study is performed for the direction of radiation R/sub perpendicular/ perpendicular to the magnetostatic field B0. The least-damped-roots approximation is used which allows the inclusion of two modes, the main mode (m) and the cyclotron harmonic mode (h), the contribution of each being essential for the total potential estimate. It appears that under dense plasma conditions, only the mode h has a low-damped part in its dispersion curves and is primarily responsible for the behavior of the total potential Vertical BarphiVertical Bar. The potential then exhibits two different scales in its amplitude modulation as a function of R/sub perpendicular/ and Ω. The small-scale pattern reflects the phase variation of this mode and the large-scale pattern reflects both diffraction and directional effects. A careful diagnosis is necessary since, according to the distance R/sub perpendicular/, a main peak can occur at a frequency which is not the expected usual resonance frequency. Similar results are obtained for various dense plasma conditions provided that the electron plasma frequency Ω/sub p/ is larger than the higher gyroharmonic of the dispersion branch of concern, i.e., presently Ω/sub p/>>2