Study of the Relationship between Type I ELM Severity and Perturbed Electron Transport in NSTX*

Global T$_{e}$ profile crashes of 10-30{\%} amplitude are observed following large Type I ELMs in some H-mode NSTX discharges. While the soft X-ray (SXR) data indicates that the ELM itself is causing only a peripheral T$_{e}$ perturbation, the propagation of the cold pulse initiated by the ELM is anomalously fast ($\sim $ms timescale) and can extend to the core of the plasma. The estimated perturbed $\chi _{e}$ is a few hundred m$^{2}$/s for $\rho \quad >$ 0.4, and a few tens of m$^{2}$/s for $\rho \quad <$ 0.4. This behavior suggests a link between the severity of Type I ELMs and the perturbed electron thermal transport on NSTX. We produced controlled perturbations at the plasma edge by injecting small low-Z pellets into ELMy H-mode plasmas, and compared the ELM and pellet induced cold pulse using multi-color SXR imaging. In plasmas with large Type I ELMs the pellet perturbation has a similarly large effect on the global T$_{e}$ profile. In recently developed high triangularity regimes with smaller ELM perturbations, the pellet induced perturbations are likewise reduced.