Asymmetric electron cyclotron emission from non-thermal plasmas subject to a generalized Kirchhoff's law

The electron cyclotron emission (ECE) spectra characteristic of a non-thermal plasma comprising of a current-carrying superthermal electron tail, for which a generalized Kirchhoff's law holds true, are evaluated for both the extraordinary (X) and ordinary (O) mode, for perpendicular as well as oblique propagation on the outboard side of the plasma; both higher order finite-Larmor-radius effects and harmonic overlap are accounted for. Besides a spectrally narrow non-thermal feature occurring at frequencies downshifted to both first (in X and O-modes) and second (X-mode only) harmonic cyclotron frequencies outside the plasma, the non-thermal ECE contributes a spectally broad enhancement to the thermal emiision, a salient characteristic of the non-thermal ECE being the asymmetry with espect to the parallel refractive index. The relevance of the upshifted second harmonic ECE of the X-mode is discussed along with the concomitant downshifted third harmonic emission for both optically thick and optically thin plasmas. (Author)