Contribution of Ne ions to radiation enhancement in JT-60U divertor plasmas

The emission spectra from Ne seeded divertor plasmas of JT-60U are measured by an absolutely calibrated vacuum ultraviolet spectrometer and analyzed with a collisional-radiative model. The radiative power of Ne ions from the inner divertor plasma in the detached phase contributes 55% of the total radiative power while that in the attached phase contributes 34% even at a similar Ne seeding rate. From an analysis of the intensity ratios of Ne VIII spectral lines, it is found that volume recombination of Ne IX to Ne VIII occurs more frequently in the detached plasma, enhancing Ne VIII density. This is one of the leading processes that enhances the radiative power from highly charged Ne ions in the detached plasma.