DENSITY FLUCTUATIONS AND THE ACCELERATION OF ELECTRONS BY BEAM-GENERATED LANGMUIR WAVES IN THE SOLAR CORONA

Abstract

Non-thermal electron populations are observed throughout the heliosphere. The\nrelaxation of an electron beam is known to produce Langmuir waves which, in\nturn, may substantially modify the electron distribution function. As the\nLangmuir waves are refracted by background density gradients and as the solar\nand heliospheric plasma density is naturally perturbed with various levels of\ninhomogeneity, the interaction of Langmuir waves with non-thermal electrons in\ninhomogeneous plasmas is an important topic. We investigate the role played by\nambient density fluctuations on the beam-plasma relaxation, focusing on the\neffect of acceleration of beam electrons. The scattering of Langmuir waves off\nturbulent density fluctuations is modeled as a wavenumber diffusion process\nwhich is implemented in numerical simulations of the one-dimensional\nquasilinear kinetic equations describing the beam relaxation. The results show\nthat a substantial number of beam electrons are accelerated when the diffusive\ntime scale in wavenumber space \\tau_D is of the order of the quasilinear time\nscale \\tau_ql, while when \\tau_D << \\tau_ql, the beam relaxation is suppressed.\nPlasma inhomogeneities are therefore an important means of energy\nredistribution for waves and hence electrons, and so must be taken into account\nwhen interpreting, for example, hard X-ray or Type III emission from\nflare-accelerated electrons.\n