Plasma development in the low-pressure channel spark for pulsed intense electron beam generation

Pulsed intense electron beams with remarkable parameters are generated in transient hollow-cathode discharges (THCD). The channel spark is different from the other THCD configurations with respect to the low gas pressure and the tube geometry, which consists of a dielectric capillary tube and an anode mounted on its external surface. In this paper, the channel-spark discharge is systematically studied by electrical and fast shutter camera measurements. The buildup of electrostatic field and the equipotential lines are calculated by the numerical code Electrostatic Field (ElFi) 3.0. The influence of the gas pressure, breakdown voltage, and external capacitance on the discharge current and the beam current are outlined. Depending on the gas pressure, two different discharge modes are observed, i.e., the high resistive and the regular modes, which can be distinguished by the shape of the electrical signals. The plasma development in these modes is studied by electrical and fast shutter camera measurements, performed spectrally integrated and with interference filters to separate the emission of the ions originating from the working gas and capillary material. Compared to the pseudospark, the plasma development in channel spark presents similar as well as specific features due to the low gas pressure and to the capacitive anode-plasma coupling.