Understanding The Energy Balance Of A Surface Barrier Discharge For Various Molecular Gases By A Multi-Diagnostic Approach

Electrical and calorimetrical measurements were performed to obtain insight into the energy transformation from input power to the power available for the plasma treatment of substrates in a diffuse coplanar surface barrier discharge used as plasma source and operated in air, N2, O-2, and CO2 at input power of up to 380W. Overall input power and applied electrical power were measured, and a conversion of 90% was determined with a constant loss of 30W for the operation of the control unit. Measurements of the temperature gradient were performed for the electrode oil cooling to identify the power loss due to cooling. With roughly 50% of the applied electrical power, it turned out to be the largest loss term. A ceramic passive thermal probe was used to determine the energy flux from the plasma to a substrate. Highest energy flux values were found to be about 500mW=cm(2) using air as working gas. Conversion efficiencies from the available electrical power via discharge to the power used for substrate treatment of 50%-35% depending on the working gas (highest for air, lowest for CO2) were determined. Investigation on the spatial expansion of the surface discharge showed a dependence of the energy flux from the distance above the electrode. The energy flux maximum shifts to larger distances if no oxygen is present in the working gas.