Cold atmospheric pressure helium plasma jets are increasingly used in many processing
applications, due to a distinct combination of their inherent plasma stability with excellent
reaction chemistry often enhanced downstream. Despite their widespread usage, it remains
largely unknown whether cold atmospheric plasma jets maintain similar characteristics from
breakdown to arcing or whether they possess different operating modes. In addition to their
known ability to produce a fast moving train of discrete luminous clusters along the jet length,
commonly known as plasma bullets, this paper reports evidence of two additional modes of
operation, namely a chaotic mode and a continuous mode in an atmospheric helium plasma jet.
Through detailed electrical and optical characterization, it is shown that immediately following
breakdown the plasma jet operates in a deterministic chaotic mode. With increasing input
power, the discharge becomes periodic and the jet plasma is found to produce at least one
strong plasma bullet every cycle of the applied voltage. Further increase in input power
eventually leads to the continuous mode in which excited species are seen to remain within the
inter-electrode space throughout the entire cycle of the applied voltage. Transition from the
chaotic, through the bullet, to the continuous modes is abrupt and distinct, with each mode
having a unique set of operating characteristics. For the bullet mode, direct evidence is
presented to demonstrate that the evolution of the plasma jet involves a repeated sequence of
generation, collapse and regeneration of the plasma head occurring at locations progressively
towards the instantaneous cathode. These offer previously unavailable insight into plasma jet
formation mechanisms and the potential of matching plasma jet modes to specific needs of a
given processing application.
History
School
Mechanical, Electrical and Manufacturing Engineering
Citation
WALSH, J.L....et al., 2010. Three distinct modes in a cold atmospheric pressure plasma jet. Journal of Physics D: Applied physics, 43 (075201), 14pp.