Growth and decay of macroparticles: A feasible approach to clean vacuum arc plasmas?

Metal and carbon plasmas produced at nonstationary cathode spots are inherently contaminated with micron-size macroparticles, and their removal is typically done by guiding the plasma through curved magnetic macroparticle filters in order to spatially separate plasma and macroparticles. In this article, a possible alternative approach is discussed in which macroparticles are destroyed rather than removed. Mass and energy transfer from the plasma to macroparticles are considered. Both cold and warm ion approximations are discussed. It was found that the desired result-complete evaporation of macroparticles before arrival at the substrate - cannot be easily achieved in any case. Ion bombardment heating is reduced by thermionic electron emission when the macroparticle approaches the temperature region of strong evaporation. The heat loss;mechanisms, thermal radiation and evaporation, increase strongly with temperature, Direct heating of the macroparticle seems to be most promising. Microwave heating was ruled out because of the plasma shielding effect. The use of infrared lasers has been proposed, but this solution is likely to be uneconomical. (C) 1997 American Institute of Physics.