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

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 (alpha), relative permittivity (epsilon(r)) 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 alpha and epsilon(r). For epsilon(r )? 9, the split can be only observed with alpha < 60 degrees. The deviation gradually decreases as alpha increases from 15 degrees to 90 degrees with epsilon(r) = 9. With the increase of epsilon r from 9 to 56, the split and deviation are more pronounced with alpha = 30 degrees. The deviation gradually increases as applied voltage and d values increase from 5.5 to 10.0 kV and 19-24 mm, respectively. However, the deviation is independent of the gas flow rate of 400-2000 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 alpha variation. An increase in epsilon r results in a stronger dielectric polarization effect. Changes in alpha cause a misalignment between the propagation direction of IW and the direction of enhanced electric field. Additionally, decreasing alpha shortens the perpendicular distance (dsin alpha) 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.