Speaker
Description
In earlier papers (Sauer and Sydora, 2015, 2016) it has been shown that an electron current in a plasma is directly linked to the formation of Langmuir oscillations at the electron plasma frequency ω_e. The current may arise due to a relative drift between electrons and protons or by a drifting electron population. No kind of beam instability should be involved. The excitation of electromagnetic waves at ω_e by the current-driven Langmuir oscillations is a completely new mechanism of the generation of type III bursts. The electromagnetic radiation arises from the mode coupling between the left-hand polarized electromagnetic wave and the Langmuir wave in case of oblique propagation. The fact that no beam instability is required for the explanation of type III radiation resolves the Sturrock paradox (Sturrock, 1964) involving the incompatibility of short-lived beam instability with long-lived radiation bursts. Starting with simple considerations to the Langmuir oscillations, the system of fluid-Maxwell equations is used to calculate the amplitude of the electromagnetic field component in dependence of the driving current. By solving the nonlinear equations and using PIC simulations the second harmonic generation is additionally studied. If the electron current is caused by an electron plateau distribution which may result from a saturated beam instability, an electron-acoustic wave is excited by a similar decay process, but in the wave number range (k) far away that of the electromagnetic waves with kc/ωe~1. Measurements of type III radio bursts aboard the Parker Solar Probe (Mozer et al., 2024) in distances of about 35 solar radii indicate that the electron current related to the measured distribution function of core, halo and strahl is the driver of the simultaneously observed Langmuir waves and electromagnetic radiation.
