Charging of Macroparticles Ejected From a Pulsed Vacuum Arc

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 direction of flight and submicron to 100 mum diameter, these macroparticles often pose a contamination threat for both spacecraft-based thrusters, and thin film deposition systems. The velocity, mass and charge of copper macroparticles emitted by a 100 A arc was experimentally measured, and compared to a model based on thermionic electron emission. The macroparticle velocity was determined by using a time-of-flight velocity filter. Less than 1% of collected particles are larger than 5.7 mum, but they account for 50% of the collected mass. The charge was calculated by measuring particle deflection in a transverse electric field. 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 (q∼D2), with a 1 mum particle having a positive charge of ∼1000 electronic charges (1.6 x 10-16 C), and a 5 mum particle having a charge of ∼25000 electronic charges. The model is particle temperature dependent, and gives q∼D2 at 1750 K and q∼D1.7 at 2200 K. Arguments are also made for limitations on particle temperature due to radiative and evaporative cooling.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Aerospace Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2015

Author dc:creator

• Rysanek, Filip

Contributors dc:contributor

• Rodney Burton

• Physics, Fluid and Plasma

Language dc:language

eng

Identifier

(MiAaPQ)AAI3270015

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/85100