Ion current distribution within a toroidal duct of a filtered vacuum arc deposition system

Vacuum arcs were established on a 90 mm diam Ti cathode in a deposition apparatus consisting of a spacer, 122 mm diam annular anode, quarter torus magnetic macroparticle filter, and a deposition chamber. A toroidal magnetic field generally parallel to the torus walls of up to 20 mT was applied. The ion current in various cross-sections of the toroidal duct was measured using: (1) a disc probe of 130 mm diam oriented normal to the torus axis used to measure the transmitted ion current, and (2) a hollow cylindrical probe of 135 mm diam and 25 mm height whose axis coincided with the torus axis, used to measure ion current losses to the duct wall. The distribution of ion current loss was studied using a 8-segment hollow cylindrical multi-probe, where the individual probes were equally distributed on the circumference of a 130 mm diam circle. It was shown that: (1) the ratio of ion currents collected on the cylindrical and disc probes at first decreases with increasing the toroidal field, and then becomes approximately constant; (2) the presence of the large-diameter disc probe does not influence the value of the ion current on the cylindrical probe; and (3) the maximum ion current density near the torus walls is located in the +g direction and displaces in the -(B×g) direction with increasing the toroidal field, where g and B are the vectors of the centrifugal acceleration and the magnetic field respectively