N. Tamura, K. Ida, S. Inagaki, H. Tsuchiya, T. Tokuzawa, K. Tanaka, H. Takahashi, T. Shimozuma, S. Kubo, Y. Nagayama, K. Kawahata, S. Sudo, K. Itoh, H. Yamada and LHD Experiment Group
Edge-Core Interaction Revealed with Dynamic Transport Experiment in LHD
Date of publication:
22 IAEA Fusion Energy Conference, EXC/P8-16
Large scale coherent structures in electron heat transport of both core and edge plasmas are clearly found in plasma with a nonlocal transport phenomenon (NTP, a core electron temperature rise in response to an edge cooling) on Large Helical Device (LHD). At the onset of the NTP, a first order transition of the electron heat transport, which is characterized by a discontinuity of electron temperature gradient, is found to take place over a wide region (at least 6 cm wide) in the periphery of the plasma. At about the same time, over a wide region (about 10 cm wide) of the plasma core, a second order transition of the electron heat transport, which is characterized by a discontinuity of the time derivative of the electron temperature gradient, appears. The both large scale coherent structures are of a scale larger than a typical micro-turbulent eddy size (a few mm in this case). In order to assess dynamic characteristics of the electron heat transport state in the core region during the NTP, a transit time distribution analysis is applied to the temporal behaviors of the electron temperature gradient. The analysis results more clearly show the existence of the large coherent structures in electron heat transport. Thus the NTP observed in LHD is considered to be invoked by the interaction of those structures.