Assessment of W density in LHD core plasmas using visible forbidden lines of highly charged W ions

Abstract

Visible magnetic-dipole (M1) lines can serve as a novel diagnostic mean of tungsten in ITER and future DEMO reactors. Here a local tungsten density in core plasmas of the large helical device (LHD) is successfully assessed with the measurement of visible M1 lines emitted by W26+ and W27+. By such a measurement, (i) the radial profile of total tungsten density in the LHD core plasmas with a line-averaged electron density of ∼4 × 1019 m−3 and central electron temperature of ∼1 keV is found to be a hollow, and (ii) the total tungsten density is found to be decreased in the whole region with an increase in the electron temperature due to the onset of reheat mode. The scheme with visible M1 lines used in the present work can be also applied for the tungsten density measurement at the ITER edge plasma.