Runaway electrons in diffuse gas discharges

The paper provides a review of research data showing the role of runaway electrons in gas breakdowns and diffuse discharges in an inhomogeneous electric field at a pressure of 0.01-1.2 MPa. From the data presented the reader can grasp the idea of how such discharges develop at negative and at positive voltage polarity, what setups and conditions are best suited to detect runaway electron beams, and what factors influence their amplitude, duration, and energy. Also analyzed are the streamer mechanisms of diffuse discharges and the generation of runaway electrons in high-pressure gases in an inhomogeneous electric field. The review is supplemented with respective diagrams and with images captured at high resolution to trace the plasma dynamics of nanosecond gas discharges from early prebreakdown stages till their final diffuse appearance.