Superpower volume discharges initiated by avalanche e-beam and electron energy distribution of a volume nanosecond discharge

Properties of plasma produced in volume nanosecond high-pressure discharge and its formation conditions under elevated pressure in the gap with the cathode having small curvature radius have been investigated. Energy distribution of beam electrons and X-ray quanta of a volume nanosecond discharge in atmospheric pressure air have been studied. Several groups of runaway electrons were registered. It is shown that the basic contribution to beam current amplitude measured behind thin foils is given by the electrons having the energies of tens - hundreds of keV (smaller than amplitude of the maximal gap voltage). It has been confirmed that the fast electrons with the energies of units - tens of keV appear by 100-500 ps ahead of the main peak of the beam current that leads an increase of current pulse duration and amplitude. It is shown that the electrons with anomalous energies (above the maximal voltage amplitude in a gap) give minor contribution to beam current (less than 5%). Spectra of X-ray radiation generated in various gas diodes have been analyzed. Measuring methods of current amplitude of a subnanosecond electron beam and a formation mechanism of fast electrons and runaway electrons in volume discharges in high-pressure gases are being analyzed too.