Spectroscopic study of impurities in the JFT-2 tokamak

Impurity contamination and radiation power have been studied with a vacuum UV monochromator (10–1300 Å) on JFT-2 for typical 160-kA and 18-kG hydrogen discharges. Oxygen has been found to be a dominant impurity element (5–7% of the electron density) and to be radially distributed according to the ionization sequence. The ground level population densities of the O 6+ and O 7+ ions in the central hot region have been determined, and that of fully ionized oxygen has been also estimated, combined with enhanced bremsstrahlung radiation measurement. The radial profile of the effective ionic charge Z eff has been determined from that of the impurity ions. The Z eff value has been found to be consistent with the value derived from the electrical conductivity. The total power of line radiation from the first resonance transitions of the oxygen ions amounts to 100–50 kW (34–17% of Joule heating power).