ELMs and the H-mode Pedestal in NSTX
Authors: R. Maingi, S.A. Sabbagh, C.E. Bush, E.D. Fredrickson, J.E. Menard, D. Stutman, K. Tritz, M.G. Bell, R.E. Bell, J.A. Boedo, D.A. Gates, D.W. Johnson, R. Kaita, S.M. Kaye, H.W. Kugel, B.P. LeBlanc, D. Mueller, R. Raman, A.L. Roquemore, V.A. Soukhanovskii, and T. Stevenson
Date of PPPL Report: July 2004
Presented at: the Sixteenth International Conference on Plasma Surface Interactions in Controlled Fusion Devices (PSI16), 24 - 28 May 2004, Portland, Maine USA.
We report on the behavior of ELMs in NBI-heated H-mode plasmas in NSTX. It is observed that the size of Type I ELMs, characterized by the change in plasma energy, decreases with increasing density, as observed at conventional aspect ratio. It is also observed that the Type I ELM size decreases as the plasma equilibrium is shifted from a symmetric double-null toward a lower single-null configuration. Type III ELMs have also been observed in NSTX, as well as a high-performance regime with small ELMs which we designate Type V. These Type V ELMs are consistent with high bootstrap current operation and density approaching Greenwald scaling. The Type V ELMs are characterized by an intermittent n=1 MHD mode rotating counter to the plasma current. Without active pumping, the density rises continuously through the Type V phase. However, efficient in-vessel pumping should allow density control, based on particle containment time estimates.