Spectroscopic Diagnostics of Non-Maxwellian Electron Velocity Distribution Function in the Large Helical Device

Abstract This paper reviews studies of non-Maxwellian electron velocity distribution function (EVDF) measured via line emission spectroscopy and spectropolarimetry in the Large Helical Device (LHD). Information on where and under what conditions the non-Maxwellian EVDFs are generated can substantially affect plasma confinement. Since different atomic transitions exhibit different sensitivities to momenta of incident electrons, spectroscopic analysis of line intensities and their polarization enables the investigation of both the shape and anisotropy of the EVDF. Measurement techniques and their results are summarized across a broad temperature range, covering both edge and core plasmas in LHD. The results are compared with plasma parameters obtained from other diagnostic systems, and the dynamics of passing and trapped electrons are discussed.