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(EX2/5) Enhanced D-Alpha H-mode Studies in the Alcator C-Mod Tokamak

E. S. Marmar¹⁾, R. L. Boivin¹⁾, C. Fiore¹⁾, J. A. Goetz¹⁾, R. S. Granetz¹⁾, M. J. Greenwald¹⁾, A. Hubbard¹⁾, J. Hughes¹⁾, I. H. Hutchinson¹⁾, J. Irby¹⁾, B. LaBombard¹⁾, Y. Lin¹⁾, B. Lipschultz¹⁾, A. Mazurenko¹⁾, D. Mossessian¹⁾, T. Sunn Pedersen¹⁾, M. Porkolab¹⁾, J. Rice¹⁾, G. Schilling²⁾, J. A. Snipes¹⁾, G. Taylor²⁾, J. L. Terry¹⁾, S. Wolfe¹⁾, S. Wukitch^1)
 
1) MIT Plasma Science and Fusion Center, Cambridge, MA USA
²⁾ Princeton Plasma Physics Laboratory, Princeton, NJ USA

Abstract.  A favorable regime of H-mode confinement, seen on the Alcator C-Mod tokamak is described. Following a brief period of ELM-free H-mode, the plasma evolves into the Enhanced D-Alpha (EDA) H-mode which is characterized by very good energy confinement, the complete absence of large, intermittent type I ELMs, finite impurity and majority species confinement, and low radiated power fraction. Accompanying the EDA H-mode, a quasi-coherent (QC) edge mode is observed, and found to be responsible for particle transport through the edge confinement barrier. The QC-mode is localized within the strong density gradient region, and has poloidal wavenumber k_$\theta$ $\simeq$ 5cm^{- 1} and lab-frame frequency of $\simeq$ 100 kHz. Parametric studies show that the conditions which promote EDA include moderate safety factor ( q₉₅ > 3.5), high triangularity ( $\delta$ > 0.35) and high target density ( n_e > 1.2×20m^{- 3}). EDA H-mode is readily obtained in purely ohmic and well as in ICRF auxiliary-heated discharges.

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