A magnetic filter was inserted between the cathodic arc plasma source and chamber to reduce the amount of macroparticles transmitted from the plasma to the sample. The plasma output of the magnetic filter was determined as a function of magnetic field and bias voltage, for the cases when the bias was applied to the entire duct wall or to a Bilek bias plate alone. The factors affecting plasma diffusion in the duct were investigated. As well as collisional and inhomogeneous magnetic field effects, our computer simulation and experimental results indicate that the E