Determination of iron density at the plasma center using radial profile of FeKα lines in LHD

Radial profiles of Kα X-ray spectra of metallic impurities have been measured using an assembly of soft X-ray pulse-height analyzers in Large Helical Device. The assembly is quipped with a radial scanning system, which gives us detailed profile information, especially in long pulse discharges. The local emissivity profiles of the Fe-Kα X-ray spectra have been quantitatively obtained by an Abel inversion technique. The density profile of the iron impurity in each charge state is analyzed using the energy shift profiles of the Fe-Kα spectra with the help of an impurity code analysis. As an example of the present method, the iron density of 1.2 x 109 cm-3 in the plasma center is obtained at the line-averaged electron density of 2.6 x 1013 cm-3. (author)