Modes of generation of runaway electron beams in gasis at high pressure

Summary form only given. The characteristics of runaway electron beams downstream of a foil anode were studied at high pressures of helium, hydrogen, neon, and nitrogen. High-voltage pulses were applied to the tubular cathode - plane anode gap. The SLEP-150 generator, with no transmission line, produced voltage pulses of amplitude ~160 kV across a high-resistance load; the incident wave amplitude in the transmission line was ~50 kV The pulse rise time was ~250 ps at a level of 0.1-0.9 and the FWHM of the voltage pulse with a matched load was ~1 ns. The use of the transmission line in the SLEP-150 generator allowed recording the incident and reflected voltage waves and to recover the voltage across the gap during the generation of the electron beam. The RADAN-220 generator produced voltage pulses of amplitude 250 kV, FWHM with a matched load 2 ns, and rise time 0.5 ns. It is shown that the highest amplitudes of a supershort avalanche electron beam (SAEB [1]) of pulse duration about 100 ps are attained in helium, hydrogen, and nitrogen at a pressure of ~60, ~30, and ~10 torr, respectively. Decreasing the pressure 1.5-2 times of helium (p