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 N-2 shielding gas impinging on a liquid anode as measured by Thomson scattering spectroscopy. A stable radial plasma contraction and significant plasma-enhanced N-2 mixing was found for the longest investigated pulse width (9 mu s). It was found that the plasma enhanced N-2 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.