Effects of macroparticle separation in positively biased ducts in the filtered vacuum arc deposition systems

The objective of the present work was to calculate the influence of positive bias on macroparticle (MP) how in a curved magnetized plasma duct. A non-stationary model for MP charging and motion in the duct wall sheath was developed. Two cases of MP charging were considered: for large MPs (radii greater than or equal to 1 mu m) and small MPs (<1 mu m). MP trapping in the sheath was found in both cases. MPs may move in the sheath region along the wall by a repetitive process of electrostatic attraction to the wall, mechanical reflection and neutralization, followed by MP charging and attraction, etc. The effective sticking coefficient of the MP to the wall increases due to an increasing number of MP collisions with the wall when MP is trapped in the near wall sheath. Using experimental MP size distributions for Ti, Cu and C cathodes it was obtained that the MP transmission fraction through the filter decreases due to the trapping effect when a bias potential of +80 V is applied between the wall and the plasma. (C) 1998 Elsevier Science S.A. All rights reserved.