Study of spatiotemporal characteristics of atmospheric-pressure pulsed microwave Ar/N2 plasma jets
Generating a microwave plasma jet with a specific morphology is difficult in ambient air.In this study,a coaxial resonant discharge device with dual gas channels is constructed to generate an atmospheric-pressure pulsed microwave Ar/N2 double-layer plasma jet.In addition,the time-space evolution of the ionization process in the Ar/N2 plasma jet was studied.The following results were obtained:(1)A high-speed camera captured transient changes in the plasma jet morphology;enhanced optical radiations were observed during the initial and final stages of ionization.(2)A microwave Rayleigh scattering device characterized the spatiotemporal electron evolution process in the plasma jet;electron density values were observed to reach 1021 m-3 orders of magnitude,with an ionization wave peak on the rising and falling edges of the microwave pulse.(3)A monochromator measured dynamic changes in the transient spectra,tracking the evolution of N2+spectral lines from their initial appearance toward a steady development and final decay.Combining the results of experiments and electromagnetic simulations,it was observed that the rising and falling edges of the microwave pulse exhibited an enhanced ionization process,revealing that the spatiotemporal local enhanced ionization was responsible for the unique discharge morphology of the pulsed microwave Ar/N2 double-layer plasma jet.
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