Instability of Langmuir-beam waves: Kappa-distributed electrons

In space plasmas electron populations exhibit non-equilibrium velocity distributions with high-energy tails that are reproduced by the Kappa power-laws, and contrast with the Maxwellian distributions often used in theoretical and numerical analyses. In this work we investigate typical electron beam-plasma systems, and show the in uence of Kappa tails on the linear dispersion and stability spectra of Langmuir-beam waves. The most common scenarios invoke instabilities of Langmuir waves at the origin of radio emissions in solar ares and interplanetary shocks. However, the parametric domain of these instabilities is narrow (i.e., energetic beams but with very low density, nb=ne . 10 3), making their analytical and numerical characterization not straightforward, while the approximations used may lead to inconclusive results. Here we provide exact numerical solutions of Langmuir-beam mode, which distinguish from the classical ones (una ected by the beam), and also from electron beam modes destabilized by more energetic and/or denser beams. Langmuirbeam solutions are only slightly modi ed by the Kappa distribution of the beam component, due to its very low density. However, if the main (core) population is Kappa distributed, the instability of Langmuir-beam mode is strongly inhibited, if not suppressed. New analytical solutions are derived taking into account the more or less resonant involvement of electron core and beam populations. As a result, the analytical solutions show an improved match with the exact solutions, making them applicable in advanced modeling of weak (weakly nonlinear) turbulence.