Pulsed metallic-plasma generators

Abstract

A pulsed metallic-plasma generator is described which utilizes a vacuum arc as the plasma source. The arc is initiated on the surface of a consumable cathode which can be any electrically conductive material. Ignition is accomplished by using a current pulse to vaporize a portion of a conductive film on the surface of an insulator separating the cathode from the ignition electrode. The film is regenerated during the ensuing arc. Over 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> ignition cycles have been accomplished by using four 0.125-in (0.318-cm) diameter zinc cathodes operating in parallel and high-density aluminum-oxide insulators. A plasma consisting of cathode material is emitted at the rate of about 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-7</sup> kg for each coulomb of charge emitted. The plasma is ejected in the form of a high-velocity highly directional conical plume through a ring-shaped anode. One or more magnetic field coils may be used to control the impedance and the direction of the plume. The normal pulsed operating parameters for the generator are a few hundred volts and a few hundred amperes with pulsewidths ranging from 50 to 500 µs and repetition frequencies up to 300 pulses per second (pps). Among the applications being investigated for the generator are metal deposition, vacuum pumping, electric propulsion, and high-power dc arc interruption.