Extreme Ultraviolet Spectroscopy Applied to Study RMP Effects on Core Impurity Concentration in EAST

A space-resolved extreme ultraviolet (EUV) spectrometer has been used to observe the spatial distribution and temporal behavior of core impurity emissions at the experimental advanced superconducting tokamak (EAST), evaluating the effects of resonant magnetic perturbations (RMPs) on impurity concentration. The vertical profiles of impurity emissions from the 0 ≤ Z ≤ 450 mm range results in spectra in the wavelength range of 30 A $\le \lambda \le 500\,{\mathring {\mathrm {A}}}$ . Line emissions of impurity carbon, lithium, and iron were observed for C VI (33.7 A, 2p–1s), Li III (135 A, 2p–1s), and Fe XXIII (132.9 A, 1s 2 2s2p–1s 2 2s 2 ), respectively, whereas the unresolved transition array (UTA) of tungsten in the wavelength range of $\lambda = 48$ to 70 A is monitored to study tungsten behavior with RMP. It is clearly observed that the intensities of C VI, Li III, Fe XXIII, and W-UTA emissions are reduced by the application of RMP fields, during stages of edge-localized modes (ELMs). In addition, the reduction in Fe and W emissions with $n = 1$ and 2 (n: toroidal mode number) RMP is more significant than that of carbon and lithium emissions, i.e., ~50% to 70% for Fe XXIII and W-UTA, and ~30% for C VI and Li III. Considering that the changes in $n_{e}$ and $T_{e}$ cannot account for the impurity emissions mitigation, the EUV measurements may indicate that RMP can significantly and selectively decrease the impurity accumulation in the core region with slight effects on the main plasma. Spatial distributions of impurity emissions are also measured for different impurity species using the EUV spectrometer, confirming the space-resolved diagnostic’s feasibility to study RMP effects on core impurity concentration.