“…However, for an air gap with a highly nonuniform field only recently, with the advent of modern broadband instrumentation, it has been demonstrated experimentally (Mesyats et al, 2006(Mesyats et al, , 2008a(Mesyats et al, , 2008b) that the flow of runaway electrons (RE) is injected from the near-cathode region within the subnanosecond rise time of the accelerating pulse, it has a picosecond duration (less than 50 ps FWHM), and is not formed during the discharge, but, on the contrary, initiates the latter.…”