Interaction of atmospheric pressure helium plasma jet with tilted dielectric target: split and deviation of ionization waves

Abstract

Atmospheric pressure plasma jets (APPJs) are commonly used plasma sources in many biomedical applications. Typically, the APPJs are not always perpendicular to the target to be treated. In this paper, the effects of tilted angle (α), relative permittivity (εr) of the target, the target potential, the distance (d) and the discharge parameters on the interaction of a helium APPJ with the target are investigated. Spatio-temporal resolved images show that the ionization wave (IW) split into a surface ionization wave (SIW) and a continued propagate IW when it approaches the target. The split leads to a position deviation of the IW interaction with the target. The measurements show that the split and deviation of IWs are strongly dependent on α and εr. For εr ≥ 9, the split can be only observed with α < 60°. The deviation gradually decreases as α increases from 15° to 90° with εr = 9. With the increase of εr from 9 to 56, the split and deviation are more pronounced with α = 30°. The deviation gradually increases as applied voltage and d values increase from 5.5 to 10.0 kV and 19 to 24 mm, respectively. However, the deviation is independent of the gas flow rate of 400 to 2000 standard cubic centimeters per minute. The split of IW depends on the combined effect of enhanced electric field due to target polarization and mismatch between the propagation direction of IW and the direction of enhanced electric field caused by α variation. An increase in εr results in a stronger dielectric polarization effect. Changes in α cause a misalignment between the propagation direction of IW and the direction of enhanced electric field. Additionally, decreasing α shortens the perpendicular distance (dsinα) between IW and the target surface, further enhancing the electric field in the perpendicular direction. After the split, there is an interaction between the SIW and the IW. The propagation of the SIW is restricted to the local electric field of IW.

Investigation of electric field distribution on dielectric exposed to DC-pulsed He plasma jet with shielding gas

“…Second, the mismatch between the IW propagation direction and the enhanced electric field direction, which occurs as a result of the APPJ tilt. The details of the IWs split are discussed in our previously published work [52]. It is observed that the intensity of the IW corresponding to the falling edge of the pulse is much lower than the IW generated by the rising edge, and the SIW formed by IW cannot propagate along the surface.…”

“…The two impact points shown in the surface electric field are caused by the IW splitting above the dielectric. This phenomenon occurs due to a combination of the electric field enhancement caused by dielectric polarization effect and the mismatch of the IW propagation direction [52]. The SIW then propagates along the surface, forming an extended region to the right of the spot.…”