The Physics of Cathode Processes

Abstract

This chapter is at the heart of the book. It is the longest chapter that deals with electron emission processes. The basic mechanisms of electron emission are outlined, including thermionic emission, field emission, their nonlinear combination, as well as explosive emission. This leads to the non-stationary emission centers, which are the sources of electrons and plasma. The statistical nature of emission center ignition, coupled with self-similar features of emission centers in space and time, lead naturally to a description of cathode spots as a fractal phenomenon. If taken seriously, the old discussion of the “true” current density and “true” characteristic time of cathode spots needs to be re-evaluated: those properties are fractal down to the physical cutoffs, which are generally still below the resolution limits of the experimental equipment. As a consequence, some new features of cathode phenomena are introduced, such as the existence of transient holes in the cathode sheath.