Observation of Abrupt- and Fast-rising SOL Current during Trigger Phase of ELMs in DIII-D Tokamak
Authors: H. Takahashi, E.D. Fredrickson, M.J. Schaffer, M.E. Austin, N.H. Brooks, T.E. Evans, G.L. Jackson, L.L. Lao, and J.G. Watkins
Date of PPPL Report: June 2005
Presented at: the Thirty-Second EPS Conference on Plasma Physics (EPS 2005), 27 June - 1 July 2005, Tarragona, Spain.
Extensive studies to date of edge localized modes (ELMs) have sought their origin inside the separatrix, i.e., MHD instability from steep gradients in the plasma edge, and examined their consequences outside the separatrix, i.e., transport of heat and particles in the scrape-off-layer (SOL) and divertors. Recent measurement by a high-speed scrape-off-layer current (SOLC) diagnostic may indicate that the ELM trigger process lies, in part, in the SOL. Thermoelectrically driven SOLC precedes, or co-evolves with, other parameters of the ELM process, and thus can potentially play a causal role: error field generated by non-axisymmetric SOLC, flowing in the immediate vicinity (∼1 cm) of the plasma edge, may contribute toward destabilizing MHD modes. The SOLC, observed concurrently with MHD activity, including ELMs, has been reported elsewhere.