Spectroscopic study of the anode flare formation during the initial stage of vacuum arc discharge

Summary form only given. Generation of an anode flare in the initial stage of vacuum discharge was studied. Discharge gap was formed by a liquid-metal gallium-indium point cathode and a flat anode of the same material, with an electrode gap distance of 0.8-1 mm. The discharge was fed by pulse generator with an impedance of 50 Ohm, generating a rectangular pulse with a duration of 200 ns. Estimates show that with a charging voltage of 15-25 kV and a current amplitude of 150-250 A we can expect that power density at the anode surface could be as high as 10⁸ W/cm².Using a spectrometer combined with a intensified CCD camera, spatial and spatio-spectral pattern of plasma emission from the discharge gap were registered with a temporal resolution of 10 ns. Generation of the anode flare begins with the intensive evaporation of anode material in the spark (high-voltage) stage of the discharge. In this period, only lines of neutral atoms are present in the spectrum measured at anode position although higher charge states can be found in the cathode spectra. Intensive ionization of anode flare atoms starts when the discharge changes from the spark to an arc (low-voltage) stage. Lines of single and double charged ions consistently appear in the spectrum (lines of ions with a higher charge state were not available for registration). At the subsequent expansion of anode flare, the highest expansion velocity was observed for double charged ion lines, and the lowest one was found for neutral atoms. Expansion velocity was increasing with increasing a voltage and current (enhancement of the input energy). The mechanisms of evaporation, ionization, ion acceleration, and the role of the anode flare in the discharge are discussed.