Observation of a High Performance Operating Regime with Small Edge-localized Modes in the National Spherical Torus Experiment
Authors: R. Maingi, K. Tritz, E.D. Fredrickson, J.E. Menard, S.A. Sabbagh, D. Stutman, M.G. Bell, R.E. Bell, C.E. Bush, D.A. Gates, D.W. Johnson, R. Kaita, S.M. Kaye, H.W. Kugel, B.P. LeBlanc, D. Mueller, R. Raman, A.L. Roquemore, and V.A. Soukhanovskii
Date of PPPL Report: May 2004
Date of Revised PPPL Report: October 2004
Submitted to: Nuclear Fusion
We report observation of a high-performance scenario in the National Spherical Torus Experiment with very small edge-localized modes (ELMs). These ELMs individually have no measurable impact on stored energy but are observed by several diagnostics. The small ELMs have clear differences as compared with the ELM types reported in the literature, and this operating mode has distinct features compared with other high-performance tokamak scenarios with little or no ELMs. The ELM is termed as 'Type V' and it has a short-lived n=1 magnetic precursor oscillation rotating counter to the plasma current. If extrapolable, this scenario would provide an attractive operating regime for next-step fusion experiments.