Chaos in atmospheric pressure plasma jets

Summary form only given. Atmospheric pressure plasma jets have received considerable attention recently for use in many emerging materials processing and biomedical applications. Such devices offer the unique ability to generate plasma in a region of inert gas which is then transported in to a region of reactive gas thus simultaneously offering both stability and reactivity. Recently, experimental studies have shown that dielectric barrier plasma jets exhibit a wide range of dynamic behavior; this casts doubt over their ability to deliver process repeatability, a critical criterion in many applications. Clearly, there is a real need to understand and characterize this dynamic behavior and determine its impact upon the discharge characteristics. This contribution examines the manifestation of deterministic chaos in a dielectric barrier helium plasma jet. Power spectral density, phase-space representations, stroboscopic sections and Lyapunov exponents are all used to characterize the dynamics of the system and obtain a deep insight into its chaotic behavior. By examining two variables, namely the discharge current and gas flow rate, regions of chaotic, quasi-periodic, and periodic behavior are mapped over a wide range of operating conditions, thus providing an indirect control strategy to ensure a repeatable operation. Time, space and wavelength resolved optical diagnostics are employed to establish the impact of chaotic behavior on the plasma characteristics. It is shown that the emission intensity of key excited species varies both in terms of amplitude and ratio on a cycle to cycle basis. This independent variation of excited species suggests dynamic changes to the discharge physics and consequent plasma chemistry, a finding which has considerable implications for discharge repeatability.