Fluid Mechanics of Torch Appearance in Capillary Microplasma Jet

Atmospheric-pressure microplasma jets with long and fine torches have recently been used in industrial and medical applications, such as local dental treatment, inner surface treatment of capillaries, stimuli of microorganisms, and local cleaning of semiconductor devices. The final torch appearance is greatly dependent on both the plasma between electrodes and the gas flow that is also dominated by the configuration of the nozzle. In this study, the mechanisms of torch appearance in a dc-driven capillary microplasma jet using atmospheric-pressure air have been investigated. Experimentally measured visible torch lengths are analyzed on the basis of fluid mechanics using a fluid simulation code. The time evolution of the plasma torch is visualized with a high-speed camera, and the length and propagation velocity of the torch are presented. (c) 2009 The Japan Society of Applied Physics