Characterization of small, type v edge-localized modes in the national spherical torus experiment

TLDR: In this article, the spatial and temporal structure of the Type V ELM is presented, as measured by several different diagnostics, with one or two filaments that rotate toroidally at ∼5-10km∕s, in the direction opposite to the plasma current and neutral beam injection.

Abstract: There has been a substantial international research effort in the fusion community to identify tokamak operating regimes with either small or no periodic bursts of particles and power from the edge plasma, known as edge-localized modes (ELMs). While several candidate regimes have been presented in the literature, very little has been published on the characteristics of the small ELMs themselves. One such small ELM regime, also known as the Type V ELM regime, was recently identified in the National Spherical Torus Experiment [M. Ono, S. M. Kaye, Y.-K. M. Peng et al., Nucl. Fusion 40, 557 (2000)]. In this paper, the spatial and temporal structure of the Type V ELMs is presented, as measured by several different diagnostics. The composite picture of the Type V ELM is of an instability with one or two filaments that rotate toroidally at ∼5–10km∕s, in the direction opposite to the plasma current and neutral beam injection. The toroidal extent of Type V ELMs is typically ∼5m, whereas the cross-field (radial) ex...