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(TH2/5) Gyrokinetic Simulations of Tokamak Microturbulence

W. Dorland¹⁾, B. N. Rogers¹⁾, F. Jenko²⁾, M. Kotschenreuther³⁾, G. W. Hammett⁴⁾, D. R. Mikkelsen⁴⁾, D. W. Ross⁵⁾, M. A. Beer⁴⁾, P. B. Snyder⁶⁾, R. Bravenec⁵⁾, M. J. Greenwald⁷⁾, D. R. Ernst⁴⁾, R. Budny^4)
 
1) University of Maryland, College Park, MD, 20742, USA
²⁾ Max-Planck-Institut für Plasmaphysik, EURATOM, 85748 Garching, Germany
³⁾ Institute for Fusion Studies, University of Texas, Austin, TX, 78712, USA
⁴⁾ Princeton Plasma Physics Laboratory, Princeton, NJ, 08543, USA
⁵⁾ Fusion Research Center, University of Texas, Austin, TX, 78712, USA
⁶⁾ General Atomics, La Jolla, CA, USA
⁷⁾ Plasma Science and Fusion Center, MIT, Cambridge, MA, 02139 USA

Abstract.  Gyrokinetic simulations of ITG ( k _$\perp$ $\rho_{i}^{}$ $\lesssim$ 1) and ETG ( k _$\perp$ $\rho_{i}^{}$ $\gg$ 1) turbulence are presented. Comparisons of toroidal turbulence in these two limits provide insights into the dynamics of streamers and zonal flows. We address the generation of zonal flows by secondary instabilities and the regulation of zonal flows by collisionless tertiary instabilities. We present the first toroidal electromagnetic gyrokinetic simulations of small scale turbulence, and gyrofluid models which explain two important gyrokinetic results: (1) Near marginal stability of the linear ITG mode, the turbulence can generate zonal flows that are sufficiently weak to remain stable but sufficiently strong to suppress the linear ITG mode. This stable region corresponds to the parameter regime of the nonlinear Dimits shift. (2) ``Long'' wavelength ( k _$\perp$ $\rho_{i}^{}$ $\gg$ 1 > k _$\perp$ $\rho_{e}^{}$) ETG turbulence drives experimentally relevant thermal transport, because the secondary modes that produce saturation become weak. Finally, preliminary comparisons of simulations with experimental data are described.

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