Transport of plasma through the tubular anode and discharge stability in a vacuum arc plasma source

The influence of the magnetic field geometry and an anode insert on the ion current output, efficiency and discharge stability of a vacuum-arc plasma source were studied. Truncated cone cathodes made of either titanium or graphite were investigated. Magnetic coils produced a stabilizing field near the cathode and a focusing field with an annular magnetic cusp in the anode. The arc current Iarc was adjusted in the range of 100–110 A. The ion current Ii was measured by a flat collector. It was found, that the grid anode insert allowed the Ti cathode to be operated with magnetic field intensities in the anode up to a level sufficient for coupling with the magnetic filter field (∼ 20 mT). The maximal value of the system efficiency ratio Ii / Iarc reached 8%. Using the cusped focusing magnetic field (without the insert), Ii / Iarc = 7%. Influence of the insert in the form of a diaphragm, positions of a magnetic cusp in the anode and intensity of the longitudinal component of the focusing magnetic field on the transport efficiency of carbon plasma and on the level of ion current deviation were studied using the graphite cathode source. Optimizing the above mentioned factors provided Ii / Iarc = 8% and decreased the deviation of the ion current from ∼ 50% down to 10%.