The Use of Passive Thermal Probes for the Determination of Energy Fluxes in Atmospheric Pressure Plasmas

Atmospheric pressure plasmas receive great interest due to their industrial relevance based on lower cost compared with vacuum systems. To optimize these applications and possibly improve them, one has to understand plasma–surface interaction. This study will emphasize the energy flux as a key parameter in plasma–surface interaction. The technique of passive thermal probes (PTPs) as a suitable diagnostic to measure the energy flux is described and discussed. With such probes, the heating and cooling of a “substrate dummy” with a well-defined surface is measured. From the obtained temperature as a function of time, the integral energy flux can be deduced. This integral energy flux consists of various contributions, e.g., chemical contributions such as recombination or oxidation and kinetic energy of plasma species such as impinging ions, electrons, and neutrals. Beginning with a historical overview, this work aims to present the technique of the PTP in its entirety. This includes an explanation of the design along with different calibration and evaluation methods. Exemplary experimental results will be provided to emphasize its versatility and significance as diagnostic for modern atmospheric pressure plasma research.