Generation of high-voltage pulses with a subnanosecond leading edge in an open discharge. II. Switching mechanism

The mechanism of fast switching in open-discharge-based devices is clarified by analyzing the feature of the I–V characteristic of a quasi-stationary open discharge: at a voltage of 3–4 kV, the characteristic sharply rises, obeying the law $j\sim U^y$ with $y >$ 10 ($j$ is the current density). Such a run of the curve is explained by the fact that at $U>$ 3 kV helium atom excitation by fast helium atoms becomes the main reason for VUV radiation. Fast helium atoms result from the resonance charge exchange between He$^+$ ions moving from the anode to the cathode. In the coaxial design and in the sandwich design consisting of two accelerating gaps in which electrons move toward each other, multiple oscillations of electrons take place. This favors the generation of fast atoms and, accordingly, resonance VUV photons. Switching times as short as 0.5 ns are achieved. The minimal switching time estimated from experimental data equals 100 ps.