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(TH/P1-03) Investigations of the Role of Nonlinear Couplings in Structure Formation and Transport Regulation: Experiment, Simulation, and Theory

C. Holland1), P.H. Diamond1), G.R. Tynan2), W. Nevins3), E.-J. Kim1), J. Candy4), N. Crocker2), S. Champeaux1), O. Gurcan1), M.N. Rosenbluth1)
1) University of California, San Diego, Dept. of Physics, La Jolla, CA, USA
2) University of California, San Diego, Dept. of Mechanical and Aerospace Engineering, La Jolla, CA, USA
3) Lawrence Livermore National Laboratory, Livermore, CA, USA
4) General Atomics, San Diego, CA, USA

Abstract.  Understanding the physics of shear flow and structure formation in plasmas is a central problem for the advancement of magnetic fusion. In this paper, we report on integrated experimental, computational, and theoretical studies of sheared zonal flows and radially extended convective cells. Based on intriguing initial results suggesting increased levels of nonlinear coupling occur during L-H transitions, we have undertaken a comprehensive study of bispectral quantities in fluid and gyrokinetic simulations. Topics of study include locality and directionality of energy transfer, amplitude scaling, and parameter dependences. We also present work investigating the role of structures in transport. Analysis of simulation data indicates that the turbulent heat flux can be represented as an ensemble of ``heat pulses'' of varying sizes, with a power law distribution. The slope of the power law is shown to determine global transport scaling (i.e. Bohm or gyro-Bohm). Theoretical work studying the dynamics of the largest cells (termed ``streamers'') is presented, as well as results from ongoing analysis studying connections between heat pulse distribution and bispectral quantities.

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IAEA 2003