The Role of Helium Metastables in Radio-Frequency Driven He/O_2 Atmospheric Pressure Plasmas: Measurement and Numerical Simulation

摘要

Absolute metastable He(2 ~3S_1) atom densities were measured in a capacitively-coupled 13.56 MHz driven atmospheric pressure plasma operated in technologically relevant helium-oxygen mixtures by tunable diode-laser absorption spectroscopy. The results are compared to a one-dimensional numerical simulation, which includes a semi-kinetical treatment of the pronounced electron dynamics and the complex plasma chemistry. The main formation mechanisms for metastable helium atoms are identified and analyzed, including their pronounced spatio-temporal dynamics. Penning ionisation through helium metastables is found to be significant for plasma sustainment, while it is revealed that helium metastables are not an important energy carrying species into the jet effluent and therefore will not play a direct role in remote surface treatments.