Generation of Heavy Metal Ions with Charge States 17+in Pulsed Vacuum Arc

The generation of highly charged metal ions in vacuum arc plasmas is of interest to plasma physicists because of the possibility to extract new data on the ionization in cathode spots. In practical terms, e.g., in metal ion sources, increasing the ion charge provides a proportional increase in ion energy at a given accelerating voltage. In the last two decades, various techniques have been used to increase the ion charge states: by applying a strong magnetic field to the cathode region of a vacuum arc and an additional microwave power to the discharge plasma, by injecting an electron beam into the discharge region and applying a short high-current pulse to the discharge gap. In the paper, we present new results on the generation of heavy metal ions with very high charge states in the plasma of a pulsed vacuum arc at a current of several kiloamperes and pulse duration of a few microseconds. The mean charge state of bismuth ions in the plasma can range to over 12.5+ at a maximum ion charge higher than 17+. The influence of the discharge parameters and gap geometry on the charge state distribution is discussed.