Propagation Dynamics of Fast Electron Beam and Its Electron Cyclotron Maser Emission

Abstract

Fast electron beams (FEBs) and coherent radio bursts both are very common plasma activity phenomena in the cosmos. The electron cyclotron maser (ECM) instability driven by FEBs trapped in magnetic fields can directly amplify radio wave radiations. It has been applied successfully to explain coherent radio bursts from a planet’s magnetosphere, such as the auroral kilometric radiation at Earth and the decametric radiation at Jupiter. On the other hand, however, there is still significant controversy when applying it to solar radio bursts (SRBs) due to some heavy difficulties in the conventional ECM instability. Taking account of the electrodynamics effects of FEBs during their passage through the ambient plasma, we present a novel mechanism for the ECM instability from FEBs, in which the Alfvén wave (AW) generated by the electric current instability of the FEB, called the self‐generated AW, plays an important role. The enhanced AW not only influences considerably the motion of individual electrons of the FEB, but also changes significantly the physical characteristics of the ECM emission as a collective coherent mode excited by the FEB. In particular, this novel ECM instability can well overcome the main difficulties of the conventional theory, which are often encountered in the explanation of SRBs. The present results imply that this novel ECM instability may be applied to coherent radio bursts in wider magnetic plasma environments from the solar atmosphere and planetary magnetospheres in the solar system to exoplanets and other astrophysical objects outside the local cosmos.