Effect on transferred ac arc plasma stability of increasing ambient temperature and superimposing pulse at current zero point

Abstract

The use of alternating current (ac) arc plasma involves a problem of instability of the arc plasma at current zero point. This paper describes the effects of ambient temperature and of superimposing a pulse current on stability of the ac argon arc plasma; the pulse current (10 A) is superimposed on an ac current only at each current zero point. The ac arc plasma is generated between a tungsten electrode of a plasma torch and a copper counter electrode in a chamber. The ac current is 100-500 Arms and the arc plasma length is 40 mm. As the ambient temperature increases from 300 K to 900 K, the stored energy in the arc plasma increases and the required supply voltage to stabilize the arc plasma decreases by about 20% (from 270 to 220 Vrms). Additionally, superimposing a pulse current on an ac current causes the required supply voltage to decrease by about further 20% (from 220 to 180 Vrms).