Main Species and Physicochemical Processes in Cold Atmospheric‐pressure He + O₂ Plasmas

Abstract

The main species and chemical processes in low‐temperature atmospheric‐pressure He + O2 plasmas are identified using a comprehensive global model. The simulation results highlight the significance of Penning processes at low oxygen concentration, and the increasingly important role of electron attachment as the oxygen concentration increases. With increasing the oxygen concentration, the electron energy dissipation shifts from elastic collisions with He to dissociative excitation and attachment of O2 molecules, and large ions (${\rm O}_{3}^{ + } $, ${\rm O}_{4}^{ + } $) become the dominant charged species. Generation and loss of ROS (O, O(1D), O(1S), O2(a1Δg), O2(b1∑ g+), O3) relevant for biomedical applications are discussed.

1-D fluid model of atmospheric-pressure rf He+O2 cold plasmas: Parametric study and critical evaluation

“…16 where the main species and dominant reactions in HeþO 2 plasmas were selected out of 250þ reactions. In that study 3 regimes were identified based on the oxygen concentration in the background gas.…”

“…16 Besides the main 55 reactions identified in Refs. 16 and 5 additional reactions that were neglected due to the overestimation of the radial flux in the previous study 16 have been incorporated. The paper is organized as follows.…”

“…These have been identified as the main chemical species=reactions in a previous study that used a comprehensive chemistry model with 250þ reactions. 16 Besides the main 55 reactions identified in Refs. 16 and 5 additional reactions that were neglected due to the overestimation of the radial flux in the previous study 16 have been incorporated.…”

“…14 Global models of low-temperature atmospheric-pressure plasmas in ArþO 2 , HeþO 2 and HeþH 2 O have recently been reported. [15][16][17][18] Global models, however, are a crude approximation of the actual discharge because in most atmospheric-pressure plasmas local kinetics prevail and inhomogeneous spatiotemporal profiles are routinely observed experimentally. 19 Fluid models are a better representation and have been used to study atmospheric-pressure electronegative discharges, revealing interesting features.…”

“…The electronegative character of O 2 and H 2 O containing plasmas and their complex chemistry results in intricate plasma dynamics and chemical kinetics that are gradually being unraveled by growing number of experimental and computational studies. [12][13][14][15][16][17][18] Accounting for a complete chemistry model in a fluid simulation is computational demanding and therefore simpler global models are often used to identify the main chemical pathways in the discharge. Global models determine volume-averaged quantities eliminating spatial gradients and reducing the computational cost.…”