H-mode edge physics in NSTX and Alcator C-Mod

In NSTX (National Spherical Torus Experiment), ELMs (Edge Localized Modes) are observed using a fast-framing camera to interact with an inner-wall MARFE (Multi-faceted Asymmetric Radiation From the Edge), leading to partial burn-through of the MARFE during the ELM cycle [1]. We reexamine the MARFE stability [2] to attempt an explanation of the MARFE/ELM dynamics in NSTX. The contribution of ion self-diffusion [3,4] to the radial electric field is estimated for an L-H transition in Alcator C-Mod. \newline [1] R. Maqueda, et al., Bull. Am. Phys. Soc., \textbf{51}(7), 237 (2006); \newline [2] F. Kelly, et al., Bull. Am. Phys. Soc. \textbf{51}(7), 237 (2006); \newline [3] A. Simon, Phys. Rev. \textbf{100}, 1557 (1955); \newline [4] C. L. Longmire and M. N. Rosenbluth, Phys. Rev., \textbf{103}, 507 (1957).