Power outflux from the plasma: an important parameter in surface processing

Abstract

In this work we characterize a low-power radio-frequency atmospheric plasma (plasma needle) in terms of dissipated (input) and emitted power per unit surface (power outflux). The plasma is a non-thermal source, used for treatment of biological tissues and other vulnerable surfaces. A calibrated thermal probe is used to determine the power emitted from the plasma towards treated surfaces. Transmission of the emitted plasma power through various media (solid layers, fluids and physiological media) is studied for a broad range of plasma conditions. These data give insight into various contributions to the power outflux (thermal conduction, radiation and energetic species), as well as the penetration depth of the plasma into treated objects. The power outflux is shown to be a very important parameter, which determines the performance of the plasma tool. For the effectiveness and reproducibility of the process the power outflux is much more important than the nominal power setting. Thus, a thermal probe should become a standard control unit in surface processing reactors.

Numerical description of discharge characteristics of the plasma needle

“…In Ref. 18 powers are reported in the range of 0 -50 mW, however, here the applied voltage to the needle is not given, which makes the figures reported in this paper unsuitable for direct comparison. In addition to the experimental uncertainties, a further reason for this discrepancy could be that in the model the electric field at the tip of the needle is underestimated due to a limited sharpness of the needle as a result of the coarseness of the numerical grid.…”

Calorimetric Probes for Energy Flux Measurements in Process Plasmas

“…• Many of them offer the possibility to treat heat sensitive materials, tissue or living cells [40,93,[95][96][97][98][99][100].…”

“…Especially for the latter applications but also for the treatment of temperature sensitive materials like polymers, where the thermal load should be as low as possible to prevent the treated material from getting melted or burned, the knowledge of the energy fluxes and the resulting surface temperatures is of important interest. Even though the number of different atmospheric pressure plasma sources increased dramatically, only few applications of calorimetric probes for energy flux measurements can be found in the literature [40,41]. Due to the small size and strong spatial inhomogeneities, the interpretation of the measurements is quite difficult.…”

“…Due to the small size and strong spatial inhomogeneities, the interpretation of the measurements is quite difficult. However, if a quantitative description cannot be given, at least the maximum substrate temperature [41], the temperature distribution across the substrate [101,102] or the ratios of the different contributions [40,41] are interesting and important characteristics.…”

“…Also rf [24,[32][33][34][35][36] or microwave [24] plasmas and ion beams [37] for surface modification have been investigated. Further examples are hollow cathode plasma jets [21] and plasma downstream reactors (PDR) [15,38,39] or atmospheric pressure plasmas like plasma needle [40] and non-thermal atmospheric pressure plasma jets [41]. Since dusty plasmas received growing interest also the stationary temperature of micro particles (≈10-200 µm) which are confined in the sheath region are used to calculate energy fluxes towards their surfaces in order to obtain information about the surrounding plasma [42,43].…”