Impurity Transport and Its Application to Ion Temperature Measurement in JT-60U Divertor Plasmas

The ratio of population densities of C3+ excited levels, C3+(3p2P3⁄2), C3+(n = 6), and C3+(n = 7), indicates that C3+(n = 7) is predominantly excited by electron collision with the ground state of C3+ in attached plasmas. Hence, Doppler broadening of the C IV (n = 6-7) spectral line provides C3+ temperature. Regression analysis of the spectrum results in two C3+ temperature components. The higher C3+ temperature ranges from 50 eV to 150 eV, the lower around 20 eV. From the results of the analyses with plasma and impurity transport codes and a collisional-radiative model, the higher and the lower C3+ temperature correspond to the C3+ temperature of the common flux (divertor) plasma and of the private plasma, respectively. In the inner divertor, C3+ temperature is close to D+ temperature, and the C IV spectral line is predominantly emitted around the inner divertor leg. Therefore, it is concluded that D+ temperature around the inner divertor leg can be measured from the C IV spectral line. On the contrary, it is found difficult to measure the D+ temperature in the outer divertor.