Whistler excitation by electron beams in laboratory plasmas

Abstract

Laboratory plasma experiments have demonstrated their prime importance as essential and powerful tools for modeling and understanding many basic plasma physics phenomena as well as space and astrophysical processes. This review discusses laboratory experiments devoted to electron beam interaction with waves in magnetized plasmas, in physical conditions relevant to natural space phenomena or controlled experiments involving artificial beam injection. The study of physical processes governing the conversion of beam kinetic energy into whistler emission as well as the efficiency and the directive patterns of the resulting wave radiation is of great importance not only for basic and space plasma physics, but also for various applications. In particular, recent experimental results on the interaction of a modulated electron beam spiralling in a magnetized plasma with the whistler waves that it radiates through various excitation mechanisms are presented. Whistler emission through resonant Cherenkov and cyclotron processes has been demonstrated and characterized for the first time in a laboratory experiment when injecting a modulated electron beam into a magnetoplasma. By choosing beam and plasma parameters, these emissions could be separated from transition radiation due to interactions in the region of the beam source. Experimental investigation of fast processes produced by the injection of a single short-time current pulse of the order of 10 ns is also described, demonstrating different types of transient plasma responses depending on the nature of the whistler excitation mechanism involved.