Properties of Intermittent Bursts in Edge Plasma of LHD

抄録

In edge plasma in the Large Helical Device (LHD), incoherent fluctuations with intermittent density bursts were observed with a two-dimensional lithium beam probe that can measure electron density and its fluctuation two-dimensionally. Statistical analysis using a probability denstiy function (PDF) showed that those bursts have the characteristics of blobs, which have been observed in tokamaks. Two-dimensional PDF analysis indicates that the blobs originate in the ergodic layer outside the last closed flux surface and move to the outer region. Wavelet analysis showed that the direction of blob propagation is not always outward but is sometimes in arbitrary directions. These characteristics may be a result of the complicated magnetic field structure of the heliotron configuration.