Investigation of metallic element separation effects in rotating cathode arcs

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Abstract
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 endplates of the device was examined with a scanning electron microscope revealing macroparticles 1 - m in diameter on a smooth background film. Energy dispersive x-ray analysis showed differences in the composition of macroparticles of different sizes, and between macroparticles and the background deposited film. It is concluded that the dominant separation effect is likely to be associated with preferential vaporization of copper from the constantan cathode rather than from the particles in flight. Cross correlation of optical signals from an array of three photodiodes yielded information about the velocities of plasma non-uniformities. Two types of non-uniformity were identified: cathode arcs and striations associated with the ionization instability. The velocities and orientations of the non-uniformities were measured as a function of magnetic field. The cathode arcs moved in the retrograde direction with velocities increasing to at the highest magnetic field of 0.2 T.

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