Coherent radio emission involves four main aspects, in general: an energy source, a conversion mechanism to produce primary waves, in some cases a secondary conversion mechanism to produce radio waves, and the physics of back-reaction on the energy source. This paper briefly reviews the underlying physics of coherent emission processes before discussing some recent advances, particularly relating to secondary conversion mechanisms and back-reactions on the source. Energy sources and emission mechanisms for primary waves are covered first. The next part is concerned with situations in which the primary waves cannot escape from source to observer, and the secondary conversion mechanisms via which indirect emission can then occur. The final part deals with the effects of emission on the energy source and recent results regarding the central importance of saturation, marginal stability, and fluctuations in the source and source-wave coupling. Illustrations are presented, which draw on examples from beam- and loss-cone-driven emission via plasma emission and electron-cyclotron maser emission in the contexts of solar radio bursts. It is demonstrated that all four aspects must be accounted for by theories of coherent radio emission in nature.
CESRA Workshop on Coronal Explosive Events
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