Generation of hydrogen isotope ions in a vacuum arc discharge with a composite zirconium deuteride cathode

The mass and charge composition of the plasma of a vacuum arc with thick and film-type zirconium cathodes containing deuterium and hydrogen is investigated experimentally and theoretically. For a thick cathode, it is shown that such a system ensures effective generation of deuterium ions with an integral fraction per arc current pulse of approximately 60%; the maximal concentration of deuterium is observed at the initial stage of the arc operation. In the case of the film cathode, such a concentration of hydrogen isotopes can be attained for currents exceeding 400 A and for an arc duration at a level of a few tens of microseconds. Occlusion of deuterium in the cathode leads to additional energy expenditures for its ionization and, as a consequence, a decrease in the average charge of ions of the cathode material in the arc plasma. Deuterium in the cathode spot is ionized completely, and the drift velocity of its ions almost coincides with the velocity of ions of the cathode material due to the high frequency of ion-ion collisions in the cathode region. The interaction of a dense ($\sim$ 10$^{20}$ cm$^{-3}$) cathode-spot plasma with microinhomogeneities of the cathode surface leads to the development of thermal instability in them over time intervals that do not exceed tens of nanoseconds.