Electron energy distribution functions in a dual-frequency plasma jet at atmospheric pressure

Abstract Strong electron-neutral collisions in atmospheric-pressure plasma jets (APPJ) constrain the electron energy distribution, which governs plasma chemistry. Here, we demonstrate phase-resolved electron energy distribution function (EEDF) measurements in a dual-frequency (DF)-APPJ using laser Thomson scattering spectroscopy combined with Bayesian inference. The plasma jet sustained by a continuous 5 MHz sinusoidal power is modulated using a counter electrode, onto which the plasma impinges, with a 50 kHz bipolar square-wave bias. Nanosecond-resolved, incoherent Thomson scattering (TS) spectra were analyzed to determine not only electron density and temperature but also the EEDF, which quantifies deviations from Maxwellian energy distributions. We observe phase-dependent transitions in the EEDF, shifting toward a Maxwellian-like shape during negative voltage transitions and exhibiting weakly Druyvesteyn-like features during positive transitions of the applied low-frequency waveform. This study establishes a quantitative framework for time-resolved electron kinetics in DF-APPJ and highlights the potential of Bayesian-enhanced TS for kinetic analysis in highly collisional plasmas.