E-beam waves, instabilities and devices

Abstract This chapter explores the study of linear instabilities in plasmas that contain some charge-particle species which, in their unperturbed equilibria, drift with constant velocities relative to each other. Within their cold plasma description such particle species are called streams or beams, and the plasma instabilities they produce are called streaming instabilities. In addition, even the simplest single charged-particle species plasma—a stable electron beam (e-beam)—when coupled to appropriate, passive EM structures exhibit linear instability and thus present the potential for generating and/or amplifying EM signals propagating on such structures; this is at the basis of many e-beam devices for generating and/or amplifying signals at microwave frequencies. To bring out the essentials of such streaming instabilities in plasmas, or in oscillator and/or amplifying e-beam devices, the chapter considers cold and collisionless plasmas spatially-homogeneous and of infinite extent.