Direct measurement of the impurity dynamics during an ELM cycle

Abstract Using high spatial and temporal resolution spectroscopy, the first direct measurements of the impurity dynamics during an ELM cycle have been made in the DIII-D tokamak. These measurements confirm that significant impurity density is expelled by each ELM with the degree of expulsion dependent on the ELM size. The observed perturbation to the impurity density profile is comparable to that of the electron density, suggesting that all particle species are similarly affected by the ELM. Impurity confinement in the edge is observed to improve throughout the phase between ELMs and is associated with a continuous increase in the E  ×  B shear near the edge.