Transport barrier dynamics

The properties of the internal transport barriers are developed using theor y and radial transport simulations that evolve local turbulent energy densi ty with the temperature profiles. Standard ion temperature gradient models for the nonlinear radial fluxes driven by drift wave turbulence and stabili zed by flow shear are implemented in a new high resolution multiple space-t ime transport code. A dimensionless parameterization of the input power is introduced and shown to characterize the bifurcation to an internal transpo rt barrier. Examples of the interaction and feedback loops of the turbulenc e with the transport profiles are given for transport barriers as in the To kamak Fusion Test Reactor [D. J. Grove Nucl. Fusion 25, 1167 (1985)] and th e Japan Atomic Energy Research Institute Tokamak-60 Upgrade (JT-60U) [Ninom iya , Phys. Fluids B 4, 2070 (1992)]. For the JT-60U the high performance d ischarge E 27969, which reached an equivalent Q(DT) of unity, is modeled wi th an appropriate set of turbulent thermal, angular momentum and particle d iffusivities. The bifurcation analysis suggests a scaling law for the criti cal power for the onset of internal transport barriers. (C) 2000 American I nstitute of Physics. [S1070-664X(00)00411-0].