Cathode and plasma phenomena in vacuum-arc sources of hydrogen isotope ions. II. Ionization processes in the arc plasma

An experimental and theoretical study of the content of deuterium ions in arc discharge plasma was performed for deuterated zirconium cathodes. It was found experimentally that the deuterium ion percentage increased significantly with increasing arc current and decreasing arc duration, reaching 85% at kiloampere currents and few microsecond durations. In this case, a clear correlation was found between the content of deuterium ions in the arc plasma and the mean charge of zirconium ions: the higher the mean Zr ion charge, the greater the amount of deuterium ions in the plasma. A model was developed to describe the ionization processes that occur in the plasma of a vacuum arc with a deuterated cathode. It was shown that the relative content of deuterium ions in the plasma jet ejected from an individual cathode spot cell is not over 50%. The deuterium atoms are additionally ionized when the plasma jets of individual cells are mixed within a group cathode spot with high average current density. Conditions for additional ionization arise when the density of cells on the cathode surface is high, that is, at the initial stage of the discharge operation.