INVESTIGATION OF METALLIC ELEMENT SEPARATION EFFECTS IN ROTATING CATHODE ARCS

In this paper we describe the characteristics of a cylindrical plasma device in which copper and nickel are introduced into a rotating argon plasma via arcs at a constantan cathode. Metal collected at the endpl ates of the device was examined with a scanning electron microscope re vealing macroparticles 1-10 mu m in diameter on a smooth background fi lm. Energy dispersive x-ray analysis showed differences in the composi tion of macroparticles of different sizes, and between macroparticles and the background deposited film. II is concluded that the dominant s eparation effect is likely to be associated with preferential vaporiza tion of copper from the constantan cathode rather than from the partic les in flight. Cross correlation of optical signals from an array of t hree photodiodes yielded information about the velocities of plasma no n-uniformities. Two types of non-uniformity were identified: cathode a rcs and striations associated with the ionization instability. The vel ocities and orientations of the non-uniformities were measured as a fu nction of magnetic field. The cathode arcs moved in the retrograde dir ection with velocities increasing to 300 m s(-1) at the highest magnet ic field of 0.2 T.