Investigation of the afterpeaks in pulsed microwave argon plasma at atmospheric pressure


 We have studied the energy transport process in pulsed microwave argon plasmas at atmospheric pressure with a focus on the optical emission burst during the pulse-off time called afterpeak. Guided by experimental observations using nanosecond time resolution imaging and spectroscopic diagnostics, we have developed a global simulation model considering the time-varying reaction rate coefficients and non-thermal electron energy distribution. Our analysis on the generation and consumption of excited argon species reveals that the rapid drop in electron temperature during the inter-pulse time reduces the diffusive loss of ions and enhances the recombination reactions, which produces the afterpeak. Afterpeak intensity is larger for higher electron density at the pulse-on time and its evolution follows the change of electron density during the inter-pulse time, where the electron density is a bottleneck to the recombination. We also performed simulations on steady-state plasmas, revealing the effects of the plasma size and the dissipated power on the particle balance over a wide range of parameters. The improved understanding of the afterpeak dynamics can be utilized to optimize the power coupling and/or generation of reactive species.