On the mechanism of subnanosecond electron beam formation in gas-filled diodes

Abstract

Subnanosecond electron beams formed in diodes filled in with a gas at atmospheric pressure and X-rays emitted from nanosecond-discharge plasmas are studied. Both phenomena hold promise for lasing technology. A three-group separation of fast electrons in a gas-filled diode is proposed. It is found that the duration of the beam current in a diode filled with air at atmospheric pressure does not exceed 0.1 ns. It is also shown that the amplitude of the beam current attains maximum with a certain delay after the application of voltage to the discharge gap. A current of ∼400 A is detected behind the foil of a diode filled with air at atmospheric pressure. At a subnanosecond duration of the voltage pulse and the diffuse discharge, X-ray radiation is observed from the brightly glowing area of corona discharge. The mean steady-state velocities and energies of fast electrons in nitrogen are calculated. Head-on collisions are shown to control the constancy of the mean velocity of fast electrons for the field strengths E/p < 170 kV/(cm atm). At E/p > 170 kV/(cm atm), the escape of fast electrons takes place. It is particularly the head-on collisions that are decided to be responsible for the emission of X-rays from the bulk.