Electrostatic Wave Decay in the Randomly Inhomogeneous Solar Wind

Abstract Despite a few space observations where Langmuir and ion acoustic waves are expected to participate in the mechanism of electrostatic decay, this is to date believed to be the main and fastest nonlinear wave process in the solar wind. However, in such a plasma where random density fluctuations are ubiquitous, the question of whether nonlinear wave processes play a significant role in Langmuir wave turbulence generated by electron beams associated with type III solar radio bursts remains still open. This paper provides several answers by studying, owing to two-dimensional challenging particle-in-cell simulations, the dynamics and the properties of the ion acoustic waves excited by such Langmuir wave turbulence and the role they play in the electrostatic decay. The impact on this process of plasma background density fluctuations and electron-to-ion temperature ratio is studied. Moreover, it is shown that, for a typical solar wind plasma with an average level of density fluctuations of a few percent of the ambient density and a temperature ratio of the order of 1, nonlinear induced scattering off ions occurs, with small intensity low-frequency quasi-modes and only in localized plasma regions where density is depleted or weakly perturbed by low-frequency turbulence.