Spreading of atmospheric pressure plasma jet on dielectric surface

We experimentally investigated the characteristics of helium atmospheric pressure plasma jets (APPJs) spreading on dielectric surfaces. The spreading velocity and the local current on dielectric of quartz plate and polyimide (PI) film were measured by segmented electrodes together with an intensified charge-coupled device (ICCD) camera. The results show that the velocity depends on voltage polarity due to different developing mechanism. The velocities on two materials with the same thickness are similar. The velocity during positive half-cycle on quartz and the thick PI film (on the order of (2–20)×10³ m/s) is higher than that on the thin PI film (~ (1–10)×10³ m/s) due to the difference in equivalent capacitance per unit area. Interestingly, multiple reverse discharges were observed in each positive half-cycle during APPJ spreading on the dielectric surface, which is related to the accumulation and the induced electric field of the surface charges. The expansion of APPJ on dielectric surface is governed primarily by the local electric field and the surface charge-and-discharge mechanism, rather than solely by the total external energy directly deposited from the power source.