Plasma Emission Induced by Electron Beams in Weakly Magnetized Plasmas

Previous studies on the beam-driven plasma emission process were done mainly for unmagnetized plasmas. Here we present fully kinetic electromagnetic particle-in-cell simulations to investigate this process in weakly magnetized plasmas of the solar corona conditions. The primary mode excited is the beam-Langmuir (BL) mode via classical bump-on-tail instability. Other modes include the Whistler (W) mode excited by electron cyclotron resonance instability, the generalized Langmuir (GL) waves that include a superluminal Z-mode component with smaller wavenumber k and a thermal Langmuir component with larger k, and the fundamental (F) and harmonic (H) branches of plasma emission. Further simulations of different mass and temperature ratios of electrons and protons indicate that the GL mode and the two escaping modes (F and H) correlate positively with the BL mode in intensity, supporting that they are excited through nonlinear wave–wave coupling processes involving the BL mode. We suggest that the dominant process is the decay of the primary BL mode. This is consistent with the standard theory of plasma emission. However, the other possibility of a Z + W → O–F coalescing process for the F emission cannot be ruled out completely.