Dynamic transport study of electron thermal energy in nonlinear fusion plasma

In nuclear fusion plasmas, both thermal energy and particle transports governed by plasma turbulence are anomalously enhanced above neoclassical levels. Plasma turbulence induces various complex phenomena in transport processes, such as nonlinearity and nonlocality. Therefore, it is very important to clarify the relationship between plasma turbulence and anomalous transports. We have approached these complicated problems by analyzing the dynamics, which are recognized as temporal trajectories in a flux-gradient space, rather than using conventional power balance. In particular, in fusion research, it is critical to elucidate the mechanism of electron thermal energy transport, because the incoming burning plasmas are sustained by the heating of alpha particles. In Large Helical Device (LHD), the dynamic relationships between electron thermal fluxes and electron temperature gradients are investigated using modulated electron cyclotron heating and modern electron cyclotron emission diagnostic systems. Some trajectories, such as a hysteresis loop and a line segment with a steep slope, are observed in high-temperature LHD plasmas. Strong nonlinear properties in the transport are revealed by studying the dynamics.