Lawrence Berkeley National Laboratory

The cathodic arc plasmas produced by cathode spots usually include macroparticles, which is undesirable for many applications. A common way of removing macroparticles is to use curved solenoid filters which guide the plasma from the source to the substrate. In this work, an arc source with relatively small cathode is used, limiting the possible locations of plasma production. The relative position of cathodic arc source and macroparticle filtered was systematically varied and the filtered plasma current was recorded. It was found that axis-symmetric plasma injection leads to maximum throughput only if an anode aperture was used, which limited the plasma to near-axis flow by scraping off plasma at larger angles to the axis. When the anode aperture was removed, more plasma could enter the filter. In this case, maximum filtered ion current was achieved when the plasma was injected off-axis, namely offset in the direction where the filter is curved. Such behavior was anticipated because the plasma column in the filter is known to be shifted by ExB and centrifugal drift as well as by non-axis-symmetric components of the magnetic field in the filter entrance and exit plane. The data have implications for plasma transport variations caused by different spot locations on cathodes that are not small compared to the filter cross section.