Radial structure of fluctuation in electron ITB plasmas of LHD

Macro-scale fluctuations with long radial correlation are identified not only in the L-mode plasmas but also in plasmas with internal transport barrier (ITB) in Large Helical Device (LHD). Correlation technique has successfully realized the observation of electron temperature fluctuations, which are characterized by their correlation length comparable to plasma minor radius, with low frequency of ∼1-7kHz, ballistic radial propagation (at speed of ∼1km/s, order of diamagnetic drift velocity). Radial structures of fluctuations are qualitatively different between the L-mode and ITB plasmas. Dynamic response of this long-range temperature fluctuation is observed in perturbative experiments. Distortion of wave-front coincident with reduction of transport is discussed. (author)