Numerical simulation of a capillary helium and helium-oxygen atmospheric pressure plasma jet: propagation dynamics and interaction with dielectric

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