Measurements of a mass-charge plasma composition of a vacuum arc with copper cathode at the arc current weakly decaying and increasing with the velocity up to 10/sup 9/ A/s have been made. A portion of multicharged ions of a cathode material in the ion beam composition extracted from the arc plasma increases after interelectrode gap training by successive discharges. At a weakly decreasing arc current the largest quantity of multicharged ions is generated at the beginning of the pulse. Current rise velocity increase results in essential rise of content of cathode material multicharged ions and beam ions average charge in plasma several microseconds after the current rise begins.
