The double coupled microwave resonance probes and application for diagnosing atmospheric pressure plasma jet

The double-coupled microwave resonance probe (DMRP) based on the hairpin probe is proposed for diagnosing atmospheric plasma jet (n_e < 10¹⁷ m^-3 ). In this work, the resonance characteristics of DMRP are investigated by numerical simulation. It shows that two resonance peaks on the reflectance spectrum can be observed, and influenced significantly by some parameters, such as the probe separation, the distance to the handheld radio frequency atmospheric pressure glow discharge plasma jet (RF-APGDPJ) and the plasma electron density less than 10¹⁷ m⁻³. Based on two resonance modes of DMRP, the electron densities in the afterglow of RF-APGDPJ at the different rf powers and helium flow rates are diagnosed experimentally by matching the change of FWHM (Δf₁ -Δf_1,air and Δf₂ -Δf_2,air) measured by vector network analyzer with the simulated relation between the FWHM changes and the plasma density.