Understanding the energy balance of a surface barrier discharge for various molecular gases by a multi-diagnostic approach

Abstract

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, O2, and CO2 at input power of up to 380 W. Overall input power and applied electrical power were measured, and a conversion of 90% was determined with a constant loss of 30 W 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/cm2 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.

Conventional and non-conventional diagnostics of a stable atmospheric pressure DC normal glow microplasma discharge intended for in situ TEM studies

“…The positive electrode shown in figure 10(a), as well as for the grounded electrode during operation using the negative polarity shown in figure 10(d), the expected behavior with a deviation at the beginning of the heating or cooling phase is obtained. This deviation is caused by thermal inertia of the probe and was seen before [55]. Larger and unexpected deviations are found for the grounded electrode during operation using a positive polarity in figure 10(b) and for the negative electrode in figure 10(c).…”

“…The determined efficiencies in the range of approx. 80% are quite high compared to other atmospheric pressure plasmas as these offer more power loss pathways [32,55,67].…”

“…The dT-depiction method offers direct conversion to the energy flux, as the temperature change Ṫ necessary for solving equation ( 4) is directly visualized and the difference of the temperature changes is represented by the gap between the data points. Two parallel lines would be expected for a constant power influx P in and power loss P out during the plasma operation [24,26,55,56].…”