Understanding the propagation of an atmospheric pressure plasma jet inside a helical tube

Atmospheric pressure plasma jets (APPJ) have become increasingly popular in the last decades due to their practical applications in several areas including biomedicine, agriculture and food safety. During application, the APPJ may need to be confined in different designs such as straight, helix, wave, etc. In this work, we have investigated the characteristics of an APPJ inside a helical tube and compared its propagation within a straight tube of identical dimension. Plasma sources are designed by inserting a stainless steel needle electrode(s) inside linear and helical tube(s) of same inner & outer diameter(s) and operated with argon gas. For the same peak-peak length and total length of the tube, we have investigated the propagation of plasma bullets and emissions from reactive species at the outlet of the tube. Our observations show that the helical design operates at a lower gas temperature, and also produces less hydrogen peroxide than the linear plasma jet of identical configuration. This may be due to the difference in gas flow pattern (swirling vs linear) within the two types of tubes and will be explained through numerical simulations.