Miniature microwave plasma torch applicator and its characteristics

Abstract

Summary form only given. A compact microwave plasma torch has been designed and experimentally evaluated. The torch is designed to be light weight and to operate at atmospheric pressure with a torch discharge size of less than 1 mm in diameter. The potential applications of the torch are for materials synthesis, material cutting and welding, and various surface treatments. This torch employs an open ended coaxial structure of 12 mm outer diameter with the discharge located at the tip of the center conductor that is 5 mm in diameter. The discharge is formed at atmospheric pressure where the feed gas flows through a nozzle hole of 200-500 /spl mu/m in diameter located at the end of the center conductor of the applicator. The microwave plasma torch is experimentally evaluated over a range of input power and a variety of feed gas mixtures including argon, mixtures of argon with hydrogen and selected hydrocarbon gases, nitrogen, and air. This torch operates from 10's to 100's of watts of 2.45 GHz input microwave power and is able to maintain discharges over a wide range of flows from diffusional flow of radicals for gentle surface processing to high velocity flow approaching supersonic velocities. Diagnostic measurements performed include (1) gas temperature measured by optical emission spectroscopy (OES), (2) discharge power densities and, (3) discharge volume and size. These measurements are done versus absorbed microwave power and gas flow rate. The discharge size for absorbed microwave powers of 10-30 watts is about 0.7 mm in diameter and 2-4 mm long for a nozzle diameter of 0.4 mm. By using spatially resolved OES measurements, the temperature profile of the discharge is determined.