Experimental and numerical research of runaway electron generation during nanosecond timescale duration electrical discharge in pressurized gases

The phenomenon of Runaway Electron (RAE) generation during high-voltage, nanosecond timescale duration electrical discharge in pressurized gases has attracted considerable research attention and already been studied in different laboratories around the world for more than 40 years. This interest in this phenomenon is related to the study of the basic processes accompanying the formation of the dense plasma in this type of discharge and its important practical applications. The main questions that have been addressed are related to the amplitude and duration of the RAE beam and its energy spectrum and the location of the electron generation versus the type and pressure of the gas and parameters of the applied voltage. Because it is difficult to diagnose subnanosecond transient high-voltage and high-current discharge in pressurized gas and the generated RAE beam, numerical modeling of this type of discharge has become extremely important and useful for understanding the main physical phenomena governing the processes of the plasma formation and RAE generation. In this chapter, the results of experimental studies of RAE generation using different time- and space-resolved optical, spectroscopic, x-ray, and coherent anti-Stokes resonant scattering diagnostics are presented. The applied diagnostics allowed reliable data concerning the electron energy spectrum, duration of the RAE beam, and main parameters of the discharge plasma to be obtained. In addition, RAE parameters were studied using the Particle-in-Cell numerical simulations that have been developed. The results of these simulations show the dynamics of the potential and electric field distributions in the discharge gap and the time- and space-dependent location of the origin of RAE emission according to the nature of the electron emission and RAE energy spectrum.