Spectrum of fast electrons in a dense gas in the presence of a nonuniform pulsed field

The problems of gas preionization in discharges related to laser physics are considered. The propagation of fast electrons injected from the cathode in the presence of a nonuniform nonstationary field and the motion of multiplying electrons at the edge of the avalanche in the presence of a nonuniform nonstationary field are simulated. The effect of the voltage pulse steepness and the field nonuniformity on the mean propagation velocity of fast electrons and their energy distribution is demonstrated. At certain combinations of the voltage pulse rise time and amplitude and at a certain time interval, the center of gravity of the electron cloud can move in the opposite direction relative to the direction of force acting upon electrons. It is also demonstrated that the number of hard particles (and, hence, the hard component of the x-ray bremsstrahlung) increases with both an increase in the voltage amplitude and a decrease in the pulse rise time. For nonoptimal conditions of the picosecond voltage pulse, an assumption is formulated: an electron beam in gas is formed due to the electrons at the edge of the avalanche rather than the background multiplication wave approaching the anode.