Estimation of Mean Electron Energy in Helium Surface Ionization Waves on Dielectric Substrates*

The interaction of atmospheric pressure plasma jets (APPJ) with dielectric surfaces is important to applications from plasma catalysis to biotechnology. The characterization of surface ionization waves (SIW) by an APPJ was investigated as they interact with both planar dielectric surfaces and surfaces with simple geometric barriers. The APPJ was powered by a 500 ns positive DC pulse with 1 kHz rep rate. Helium was the working gas flowing into either background air or background helium with air impurities. Optical bandpass filters were used to image the 706.5 and 587.6 nm triplet transitions and estimate mean electron energy via line ratio. Estimates for mean electron energy were gathered in 2D using a gated ICCD with 5 ns time resolution. Substrates with simple step barriers of varying height were subject to study. Experimental results will be compared to results gathered by using the 2D plasma-hydrodynamics model nonPDPSIM. Results indicate that SIW propagation down step barriers has a lower energy threshold than stepping up small barriers.  Spatially dependent air mixing plays a large role in the ability to determine mean electron energy.