Numerical simulation of capillary helium and helium−oxygen atmospheric pressure plasma jets: propagation dynamics and interaction with dielectric

Abstract

<p>Atmospheric pressure plasma jet (APPJ) can be generated in capillary tubes flowing<br> with pure helium and with admixtures of oxygen into the pure helium. The jet exiting the tube<br> can be used for a variety of applications through surface interaction. In this study, a twodimensional<br> axi-symmetric model has been developed to provide insight into the evolution of<br> capillary helium plasma jet with and without the presence of oxygen admixtures and its<br> interaction with a dielectric surface placed normal to the jet axis. The model considers the gas<br> mixing of helium and ambient air and the analytical chemistry between helium, nitrogen and<br> oxygen species. Experiments were performed in similar conditions as the simulations in order<br> to get qualitative agreement between them. The numerical and experimental results show that<br> the evolution of the helium plasma jet is highly affected by the introduction of oxygen<br> admixtures. In particular, it was observed that the addition of oxygen admixtures in the helium<br> gas promotes plasma bullet propagation on the axis of symmetry of the tube (instead off axis<br> propagation for the pure helium plasma jet). On the other hand, the presence of the dielectric<br> surface (the slab placed in front of the tube exit) forces the plasma bullet to spread radially.<br> Furthermore, the plasma bullet speed decreases when the helium plasma jet is operated in the<br> presence of oxygen admixtures. The numerical results also showed that He/O2 plasma jets<br> induced much higher electric fields on the dielectric surface in comparison to the pure helium<br> plasma jet</p>