In this study, a high-power 915 MHz air microwave atmospheric-pressure plasma torch with input power up to 100 kW was investigated using optical emission spectroscopy (OES) and imaging characterization. Emission spectra were acquired from both the post-core plasma region and directly from the plasma core inside the resonator through an axial rear-view access. Molecular emission bands of OH, NO, and N₂ were identified in the UV region, while strong broadband continuous radiation dominated the visible and near infrared wavelengths, with intensity increasing systematically with power. Front-view imaging revealed significant changes in the spatial emission structure of the plasma core as a function of tangential gas flow and input power, including transitions between volume-filling and ring-shaped radiation patterns. The formation of an annular emission region was promoted by increased tangential flow and intermediate power levels, whereas lower flow rates or sufficiently high power resulted in a more homogeneous luminous zone. Side-view post-core microwave plasma OES measurements, combined with fitting to a temperature dependent simulated spectrum based on the OH transition band (X2Π → A2Σ+), yielded a post core plasma temperature of approximately 4100 K. By smoothing the continuous radiation spectrum and assuming approximate black body behavior, Wien’s displacement law was applied to estimate the maximum plasma core temperature, yielding a value in the range of 5520–5750 K. The combined spectroscopic and imaging results provide insight into the excitation behavior, thermal characteristics, and spatial structure of high-power 915 MHz microwave air plasmas.
Study of the possibility for increasing the emission of soft x-rays from the plasma of a low-energy vacuum discharge triggered by a laser