Three-dimensional fluid simulations of tokamak edge turbulence

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Abstract
Three‐dimensional (3‐D) simulations of drift‐resistive ballooning turbulence are presented. The turbulence is basically controlled by a parameter α, the ratio of the drift wave frequency to the ideal ballooning growth rate. If this parameter is small [α≤1, corresponding to Ohmic (OH) or low confinement phase (L‐mode) plasmas], the system is dominated by ballooning turbulence, which is strongly peaked at the outside of the torus. If it is large [α≥1, corresponding to high confinement phase (H‐mode) plasmas], field line curvature plays a minor role. The turbulence is nonlinearly sustained even if curvature is removed and all modes are linearly stable due to magnetic shear. In the nonlinear regime without curvature the system obeys a different scaling law compared to the low‐α regime. The transport scaling is discussed in both regimes and the implications for OH, L‐mode, and H‐mode transport are discussed.