Gyrokinetic Simulations and Multiscale Processes

Ronald Waltz
General Atomics

Abstract. A continuum global gyrokinetic code GYRO has been developed to comprehensively simulate core turbulence in actual experimental profiles and enable direct quantitative comparisons of simulated and experimental transport flows. GYRO not only treats the now standard ion temperature gradient (ITG) mode turbulence, but also treats trapped and passing electrons with collisions and finite beta , and equilibrium ExB shear stabilization all in real tokamak geometry. Most importantly the code operates at finite relative gyroradius (rho-star) so as to treat both the profile shear stabilization and nonlocal effects which can break gyroBohm scaling. The code operates in either a cyclic flux-tube limit (which allows only gyroBohm scaling) or a globally with physical profile variation. Bohm scaling of DIII-D L-mode has been simulated with power flows matching experiment within error bars on the ion temperature gradient. GyroBohm scaling is recovered for DIII-D H-modes. Impurity and neoclassical flows have recently been added. Apart from a brief discussion of mechanisms breaking gyroBohm scaling, the focus here is on gyrokinetic simulations and multiscale processes. Time scales: simulations at fixed flow rather than fixed gradient as a first step to a core steady state gyrokinetic transport code. Length scales: local versus nonlocal transport with a heuristic theory for modifying local gyroBohm transport models like GLF23. Finally, can (n=0) equilibrium profile (few ion gyroradius scale) corrugations, induced by the high-n micro-turbulence, impact the stability of low-n macro-scale MHD tearing modes?

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