Evaluation of Fluctuation of Plasmas Diagnosed by Excited-State Population Variation Using Stochastic Model Based on Relative Entropy

Evaluation method is proposed using stochastic model of plasma fluctuation based on collisional radiative model. Electron impact excitation of atoms is considered as a Wiener process, which is applied to analyze variation in excited-level populations in short time by Malliavin derivative. Relative entropy and fractional Brownian motion are introduced as indicators to evaluate how far a system is from its steady state, where both trend of entropy and contribution of radiative processes to the lifetime of excited states are taken into account. The influence of interactions with metastable atoms on the overall system is investigated in glow discharge plasma. The effects of gas temperature, pressure, electron temperature, and density on system behavior are evaluated. It is found that the high statistical weight of some excited states can act as a bottleneck in the energy relaxation throughout the system to a steady state.