PPPL-3903 is available in <a href="PPPL-3903.pdf">pdf</a> format (5.2 MB).

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<b> Stability of Microturbulent Drift Modes during Internal Transport Barrier Formation in the Alcator C-Mod Radio Frequency Heated H-mode</b>
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<b>Authors:</b> M.H. Redi, C.L. Fiore, W. Dorland, D.R. Mikkelsen, G. Rewoldt, P.T. Bonoli, D.R. Ernst, J.E. Rice, and S.J. Wukitch
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<b>Date of PPPL Report:</b> November 2003
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<b>Submitted to:</b> Physics of Plasmas</p>

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Recent H-mode experiments on Alcator C-Mod [I.H. Hutchinson, et al., Phys. Plasmas <b>1</b> (1994) 1511] which exhibit an internal transport barrier (ITB), have been examined with flux tube geometry gyrokinetic simulations, using the massively parallel code GS2 [M. Kotschenreuther, G. Rewoldt, and W.M. Tang, Comput. Phys. Commun. <b>88</b> (1995) 128]. The simulations support the picture of ion/electron temperature gradient (ITG/ETG) microturbulence driving high <FONT FACE = "symbol">c</FONT><sub>i</sub>/<FONT FACE = "symbol">c</FONT><sub>e</sub> and that suppressed ITG causes reduced particle transport and improved <FONT FACE = "symbol">c</FONT><sub>i</sub> on C-Mod. Nonlinear calculations for C-Mod confirm initial linear simulations, which predicted ITG stability in the barrier region just before ITB formation, without invoking <b>E x B</b> shear suppression of turbulence. Nonlinear fluxes are compared to experiment, which both show low heat transport in the ITB and higher transport within and outside of the barrier region.





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