Spatial localization of Langmuir waves generated from an electron beam propagating in an inhomogeneous plasma: Applications to the solar wind

Abstract

It is known from in situ observations that large‐amplitude spatially localized Langmuir waves are frequent in the solar wind, and usually correlated with the presence of suprathermal electron beams, during type III events or close to the electron foreshock. It seems that the influence of the solar wind density fluctuations on the propagation effects of the Langmuir waves play an important role in the formation of these wave packets. In this article, we focus on the mechanism of generation of localized wave packets by electron beams propagating in an inhomogeneous medium. To this purpose, we present a theoretical model based on the resolution of the high‐frequency component of the Zakharov's equation in which a source term describing the electron beam has been introduced, and show that this model is able to reproduce classical results about beam plasma instability and wave trapping in density cavities. Then we present simulation results of the generation of Langmuir wave packets in typical solar wind conditions at 1 A.U., and discuss the origin and nature of their localization.