Electrical and emission spectroscopic investigation of a self-pulsing micro hollow cathode discharge

Micro hollow cathode discharges (MHCD) consist of two electrodes separated by a thin dielectric (here: 100 $\mu $m). The discharge develops in a hole penetrating all three foils (200 $\mu $m diameter). When powered by a DC voltage of several 100 V, the discharge shows self-pulsing operation. Voltage and current measurements, optical emission measurements by an ICCD camera equipped with a microscope lens as well as the determination of electron density from the Stark broadening of the H$_{\beta }$-line are performed in argon at pressure from several 1000 Pa to atmospheric pressure. The voltage-current characteristic during self-pulsing indicates a transition from abnormal mode to spark mode as in a DC glow discharge. The pulse frequency can range from kHz up to about 1 MHz and depends on the capacitance of the discharge setup. The pulse width can be as short as several 10 ns and the current peaks can be as high as 1 A. With the appearance of the self-pulsing the electron density increases from the order of 10$^{15}$ cm$^{-3}$ during the non self-pulsing operation to the order of 10$^{16}$ cm$^{-3}$. A comparison of the plasma conductivity obtained from the performed measurements with the electrical measurements shows excellent quantitative agreement.