Macroparticle Charging in a Pulsed Vacuum Arc Thruster Discharge

A pulsed vacuum arc discharge emits a plasma as well as macroparticles in the form of micron-sized molten droplets of cathode material. Due to their trajectory and size, these macroparticles often pose a contamination threat for both spacecraft-based thrusters, and thin film deposition systems. The charge of these macroparticles was experimentally measured, and compared to a model based on thermionic electron emission at T~2500K. The model predicts and the experimental results verify that the charge on the macroparticles is positive, as compared to the negative charge expected for a DC vacuum arc. Experimental results show a roughly quadratic dependence of particle charge on the particle diameter, with a 1 μm diameter particle having a charge of approximately 1000 x 1.6 x 10 C. Model results show a roughly quadratic charge dependence for particles smaller than 1.2 μm and a roughly linear dependence for particles greater than 2 μm.