A Simultaneous Spectroscopic Measurement of the Global and Edge Local Structures in the Ion Temperature and Plasma Rotation Profiles in the Compact Helical System

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In charge exchange spectroscopy (CXS), a simultaneous observation in different plasma toroidal cross sections and/or viewing ports is required to investigate radial distributions of ion temperatures Ti(r), and poloidal rotation velocities Vp(r) in magnetically confined toroidal plasmas. In recent studies of the edge transport barrier (ETB) in the Compact Helical System (CHS), a simultaneous viewing of the vertically elongated and the horizontally elongated plasma cross sections is used to improve the spatial resolution at the edge region. The 90 fibers used for this purpose are connected to one spectrometer, and a 256 × 243 pixel sampling CCD is used to detect the diffraction image. It is found that there is a localized edge ion temperature pedestal region with ΔTi ≈ 100 eV and Δr/a ≈ 0.1, where r and a are flux surface averaged minor radii of measured surfaces and the outermost flux surface, respectively. The negative radial electric field at the edge is increased in the high confinement phase because of the increased ion pressure.
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