PIC simulation of current-driven solar type III radiation and whistler waves in an electron core-strahl plasma: Relevance to PSP and other space observations

Abstract

The aim of the paper is to demonstrate that electron current oscillations may generate electromagnetic waves as type III radiation and whistler waves without the involvement of the classical plasma emission via the coalescence of waves. PIC simulation results of an electron-core-strahl plasma without initial current compensation are presented which describe the conversion of current-driven Langmuir oscillations/waves into type III radiation whereby simultaneously whistler waves are excited. In contrast to the classical approach of Ginzburg and Zhelezniakov (1958) after which beam-excited Langmuir waves in a two-step process are converted in electromagnetic radiation, any instability is suppressed by selecting a low strahl velocity. Rather electric field oscillations at the electron plasma frequency are triggered by the initially non-compensated current of the strahl. The arising electromagnetic fields exhibit amplitude oscillations which are caused by the superposition of the two wave modes of mixed polarisation at the point of mode coupling. This basic mechanism of wave generation and transformation has already been described in earlier papers using simple fluid models. It is also the topic of the companion paper. Besides the fundamental electromagnetic radiation, the second harmonic of nearly the same intensity has been obtained which is an indication for nonlinear currents. Measurements of Langmuir waves, type III radiation and whistler waves on board various satellites in the solar wind, in particular Parker Solar Probe (PSP) observations are analysed in the light of our results. Interpretations of earlier PIC simulations are critically reviewed.