Electron hole as an antenna radiating plasma waves

Abstract

Recent observations of electron holes (e‐holes) in space plasma have led to theoretical and numerical studies which show that e‐holes in a magnetized plasma are unstable nonlinear structures. Their decay generates plasma waves in the frequency bands of lower hybrid (LH) and electrostatic whistler (EW) waves. An analysis is presented demonstrating that the e‐holes are an effective radiator of plasma waves in the above frequency bands critically depending on their scalelength (ℓ⊥) transverse to the ambient magnetic field. In this sense, an e‐hole acts like a radiating antenna. The results from 3‐D numerical simulations are presented to examine the nonlinear consequences of the radiation from e‐holes. When e‐holes have long ℓ⊥ during the initial stage of their existence, they undergo a beading process. This involves radiation of spatial Fourier components corresponding to long scalelength in the structure of e‐holes, leaving behind smaller structures. This divides the initially large e‐hole structure into several fragments. The resulting smaller structures with ℓ⊥∼ ℓ∥ eventually dissipate by radiating transversely structured lower hybrid waves.