Supershort Avalanche Electron Beam Generation in N2 and He at Quasi-Continuous Gap Voltage

Summary form only given. In the recent works e-beams with amplitudes of units-hundreds of amperes were obtained in atmospheric pressure gas diodes behind a foil. It was demonstrated that duration of a current pulse at atmospheric pressure of different gases makes ~100 ps. The SAEB duration remained subnanosecond also at pressure varied in a wide range. However, an electron beam was obtained at generator voltage above 100 kV and duration of the voltage pulse leading edge of ~1 ns and less. Whereas pioneered X-ray radiation was obtained at atmospheric pressure discharge in helium at generator voltage of no more than 17 kV. The well-known papers, where for generation e-beams at comparatively low pressures the voltages of units-tens kV and narrow interelectrode spacing (<1 mm) were used. The aims of this work were to investigate possible generation of supershort avalanche e-beam (SAEB) in nitrogen and helium at low voltage gap (~25 kV), and to define in these conditions the delay time of generation of a SAEB and its duration. Generation of a supershort avalanche e-beam in nitrogen and helium at quasi-continuos gap voltage has been shown. SAEB duration at generator voltage of 25 kV is ~200 ps at a half-height, and its delay time with respect to the voltage pulse risetime may be tens of nanoseconds. The beam current waveforms, having several subnanosecond peaks have been recorded. It was established that at SAEB generation the gap voltage is decreasing by 10-20%. The change in oscillating mode of beam current of fast electrons in a gas-filled diode at He and N₂ pressure decay was registered. Duration of the beam current of the fast electrons in an impulse increased up to several nanoseconds, and the impulse had two peaks on the osciloscope trace.