Propagation of ionization waves in atmospheric pressure plasma jets toward tilted grounded target surfaces

The propagation of the ionization wave (IW) from a pulsed helium atmospheric pressure plasma jet to tilted dielectric and metallic targets grounded was investigated via experiments and simulations. The results indicate that the IW initially propagates along the tube axis but deviates from its original direction around 3 mm above the target surface, eventually striking the tilted surface perpendicularly. This deviation occurs because the enhancement of the induced electric field above the target is not aligned with the original direction of the IW. The deviation values, defined as the distance between the IW strike point and the intersection of the tube axis with the target, ranged from 1.86 to 2.15 mm, while the surface ionization wave (SIW) propagation distance decreased from 7.63 to 1.83 mm as the relative permittivity (εr) increased from 2.55 to 56. Concurrently, the E/N at the IW head increased from 76 to 86 Td at 75 ns as εr increased. The ground potential is the primary factor causing the electric field enhancement observed above the target, while the contribution of the dielectric polarization effect is negligible. Upon striking a metal target, the IW becomes a reflected IW, which generates a secondary IW and propagates back toward the metal surface. ICCD imaging and numerical simulation reveal that a “dark area” emerges between the SIW and the secondary IW following IW reflection.