Influence of an external electrode on a plasma plume ejected from a syringe electrode inside a glass tube

Abstract

An atmospheric plasma jet device consisting of a syringe electrode inserted into a glass tube has been introduced. A high voltage is applied to the syringe electrode with a DC-AC inverter at a few tens of kHz. The external electrode on the outside surface of the glass tube is grounded. The current-voltage characteristics and the plume length are investigated with respect to the electrode gap distance d and the external electrode width w. The breakdown voltage depends on the gap distance d while the width w acts as a capacitance in the AC-discharge circuit. When the gap distance is short and the width is narrow, the breakdown voltage is lower and is accompanied by a low current by which the plume length is adjustable from 0 mm initially to a saturated value of about 10 mm as the voltage is increased after breakdown. If the device has a long gap and a wide width, a high breakdown voltage and a high current initially make a plume of finite length at the breakdown, which saturates shortly thereafter. This allows the plasma emission current and the plume length to be controlled with a short gap distance d and a narrow width w of the external electrode.