Transport of macroparticles in magnetized plasma ducts

Abstract

The cathode spot of a vacuum are produces a highly ionized energetic plasma jet of vaporized cathode material which may be directed to a substrate to form a high-quality coating or thin film, and a spray of molten droplets, referred to as macroparticles (MPs). The plasma flux can be concentrated by magnetic collimation, while the MP spray can be filtered from the plasma jet by guiding the plasma around an obstacle using a magnetic field. In the present work, the motion of the individual electrically charged MP in the straight and quarter torus plasma guides is studied, taking into account MP charging by interaction with the plasma. The influence of the electric field in the plasma, which depends on the magnetic field, on the charged MP motion is calculated. The fraction of the MPs transmitted through the toroidal plasma guide was calculated as a function of the wall potential and MP velocity for different minor to major torus radius ratios r/R. The guide wall potential has a strong effect on the transmission of MPs having velocities in the 25-100 m/s range. In the case in which r/R=0.1, with the duct at floating potential, the fraction of the MPs transmitted through the torus approaches 100% for 0.1 /spl mu/m Ti MPs having an initial velocity parallel to the duct wall. The main mechanism of MP transmission through curved ducts is repeated electrostatic reflection of the charged MP from the wall. The calculation of the MP transmission through the magnetized straight duct was compared with experiment, where a significant reduction of the MPs was obtained with an increasing of the axial magnetic field. The calculated MP transmission was close to that previously measured for 0.1 /spl mu/m MPs with 70 m/s and for 0.5 /spl mu/m MPs with 20 m/s directed velocities.