GEC Student Excellence Award Finalist Presentation - Spatio-temporal distribution of neutral radical species in an atmospheric pressure He/O₂ radio-frequency plasma jet based on a spatially 2D hybrid simulation

Radio-frequency (RF) driven micro atmospheric pressure plasma jets have numerous applications of industrial relevance (e.g., in surface manufacturing and plasma medicine), due to the efficient generation of radical species. In order to optimize these plasma processes, a quantitative understanding of how the neutral species densities build up along the jet channel, is needed, which is a result of the complex interplay between multiple processes on different timescales, including the gas flow, chemical reactions and the charged particle dynamics.

In this work we investigate the COST reference microplasma jet, operated in a He/O₂ mixture (99.5%/0.5%), excited by a single frequency waveform (with f=13.56 MHz and V_rms=250 V) for different flow velocities, based on a spatially 2D hybrid simulation. The simulation is based on a fluid model, solving the 2D continuity equation using the drift-diffusion approximation for all species, including the gas flow and chemical reactions using rate coefficients. Electron impact processes are accounted for by a Monte Carlo procedure. Based on measurements of the atomic oxygen density, we show, that this simulation method is capable of describing the COST jet in a quantitative manner, providing an agreement with experiments within 20%. We elucidate what role electron impact processes and chemical reactions play in the buildup of neutral radicals along the jet. Specifically, we show how the atomic oxygen density can reach saturation as a function of the gas flow velocity.