Designing advanced filters for macroparticle removal from cathodic arc plasmas

Curved magnetic filters are commonly used with cathodic arcs to remove macroparticles from the plasma stream, making them suitable for the preparation of smooth, dense and defect-free films. Plasma losses associated with these filters are rather high. The highest reported ion current transported through a curved macroparticle filter is 2.5% of the arc current. In this paper we show that it is possible to finely control both the shape and spatial position of the plasma beam as it passes through a curved magnetic filter by the addition of strategically placed current-carrying wires. Our modifications consisted of additional current loops at the entrance and exit of the filter to reduce the divergence of magnetic field lines there; a number of conducting wires were also placed outside the filter along its length to centre the beam in the filter. We were able to improve the plasma transport efficiency by modifying the paths of magnetic field lines through the 90° filter with the aid of computer calculation, achieving a filtered titanium ion current up to 6.3% of the arc current.