Suprathermal Spontaneous Emissions in kappa-distributed Plasmas

Abstract

A suprathermal spectral component is identified in the spontaneous emissions of kappa-distributed plasma populations, ubiquitous in astrophysical setups. Theoretical power spectra are confirmed by the simulations and capture the dispersion characteristics of electrostatic and electromagnetic eigenmodes of a quasi-stable magnetized plasma. Selectively enhanced by the suprathermal emissions are the fluctuations of fast modes (e.g., Langmuir, fast magnetosonic, or the low-wavenumber branches of kinetic Alfven and Bernstein waves) induced resonantly by the energetic (suprathermal) particles. These results have an immediate implication in spectroscopic techniques of in situ or remote diagnosis for the very hot and dense plasmas, e.g., close to the Sun, where direct measurements of plasma particles and their properties are technically impossible. Contrasting patterns of suprathermal emissions may confirm the coronal origin of the suprathermal populations observed in the solar wind.