Propagation of Ionization Waves on Dielectric Substrates in Atmospheric Pressure Plasma Jets (APPJ)

The interaction of APPJs with dielectric surfaces is important to applications from plasma catalysis to biotechnology. The propagation of ionization waves by an APPJ was investigated as they impact dielectric surfaces of varying thickness and convert to surface ionization waves (SIWs). The APPJ was powered by a +4kV 500ns DC pulse with 1kHz rep rate. Helium was the working gas flowing into room air. A gated ICCD with 5ns shutter speed was used for imaging. The surfaces consisted of stacked glass of varying thickness from 0.15 – 10.1mm. The experiments were modeled using the 2D plasma-hydrodynamics model nonPDPSIM. Surface wave velocity strongly depends on glass thickness, increasing by a factor of 3 for thicknesses of 0.15 - 1.65mm. Greater than 1.65mm the velocity saturates out to 10.1mm. Surface velocity ranges from 1.5-4.5x10⁴ m/s. Axial velocities range from 1.55-1.81x10⁵ m/s. The speed of the SIWs are well correlated with the capacitance (F/cm²) of the surface through voltage division between the SIW and dielectric that increase velocity with decreasing capacitance to a saturation point. The underlying dielectric must charge for the SIW to proceed; lower capacitance charges faster.