Electron density and electron temperature measurements in an atmospheric pressure plasma interacting with liquid anode

Plasma driven solution electrochemistry has received increasing attention during the last decade for a variety of applications including nanomaterial synthesis. We report the temporal and spatial resolved electron density and temperature for a negative pulsed DC discharge in helium with N2 shielding gas impinging on a liquid anode as measured by Thomson scattering spectroscopy. A stable radial plasma contraction and significant plasma-enhanced N2 mixing was found for the longest investigated pulse width (9 μs). It was found that the plasma enhanced N2 mixing significantly impacts the plasma morphology and electron properties. In addition, we observed a significant increase in electron temperature coinciding with a drop in electron density near the liquid anode surface, which is attributed to electron attachment and electron-water ion cluster recombination enhanced by plasma-induced water evaporation. This near anode surface phenomenon is argued to be responsible for the discharge stabilization by preventing the development of a thermal instability in spite of the significant gas heating. This increase in electron temperature near the anode suggests the presence of a significant flux of hot electrons into solution which might enable non-equilibrium electron-driven reactions in the liquid phase.