Energy flux measurements by a passive thermal probe were performed for a diffuse coplanar surface barrier discharge to determine the transfered energy to a substrate in dependence on the substrate distance to the electrode and working gas of the discharge. The largest energy flux was found at  ∼300–400 m above the electrode surface to be about 900 mW cm−2. Furthermore, an active substrate cooling mechanism could be identified within the plasma caused by gas convection flows for very small distances. Variation of the working gas (argon, molecular gas) indicates the importance of the gas and surface reactivity for the transferred energy to the substrate. Molecular gases result in a remarkably higher energy flux compared to rare gas.

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.

Passive thermal probes were applied on two different plasma spraying devices to gain a detailed understanding of the energy flux towards the substrate under atmospheric pressure. The challenge of very high thermal load was solved by using an advanced time-resolved measuring and evaluation technique. The combination with a controlled movement of the jets allowed to obtain insightful radial profiles. The energy flux to the substrate changes linearly to the electrical input power. When adding diatomic gases (H2/N2) to the gas mixture the energy flux increases significantly, suggesting a more efficient energy transport. For increasing the axial distance, the energy flux shows a quadratic reduction. The obtained radial profiles are exemplarily utilized to show the inhomogeneous effect of powder injection on the energy flux distribution.