We present analyses of mechanisms which convert radial inhomogeneity to broken k ||-symmetry and thus produce turbulence driven intrinsic rotation in tokamak plasmas. By performing gyrokinetic simulations of ITG turbulence, we explore the many origins of broken k ||-symmetry in the fluctuation spectrum and identify both E × B shear and the radial gradient of turbulence intensity—a ubiquitous radial inhomogeneity in tokamak plasmas—as important k ||-symmetry breaking mechanisms. By studying and comparing the correlations between residual stress, E × B shearing, fluctuation intensity and its radial gradient, we investigate the dynamics of residual stress generation by various symmetry breaking mechanisms and explore the implication of the self-regulating dynamics of fluctuation intensity and E × B shearing for intrinsic rotation generation. Several scalings for intrinsic rotation are reported and are linked to investigations of underlying local dynamics. It is found that stronger intrinsic rotation is generated for higher values of ion temperature gradient, safety factor and weaker magnetic shear. These trends are broadly consistent with the intrinsic rotation scaling found from experiment—the so-called Rice scaling.

No abstract

The Korea Superconducting Tokamak Advanced Research, KSTAR, is designed to operate a steady-state, high beta plasma while retaining global magnetohydrodynamic (MHD) stability to establish the scientific and technological basis of an economically attractive fusion reactor. An equilibrium model is established for stability analysis of KSTAR. Reconstructions were performed for the experimental start-up scenario and experimental first plasma operation using the EFIT code. The VALEN code was used to determine the vacuum vessel current distribution. Theoretical high beta equilibria spanning the expected operational range are computed for various profiles including generic L-mode and DIII-D experimental H-mode pressure profiles. Ideal MHD stability calculations of toroidal mode number of unity using the DCON code shows a factor of 2 improvement in the wall-stabilized plasma beta limit at moderate to low plasma internal inductance. The planned stabilization system in KSTAR comprises passive stabilizing plates and actively cooled in-vessel control coils (IVCCs) designed for non-axisymmetric field error correction and stabilization of slow timescale MHD modes including resistive wall modes (RWMs). VALEN analysis using standard proportional gain shows that active stabilization near the ideal wall limit can be reached with feedback using the midplane segment of the IVCC. The RMS power required for control using both white noise and noise taken from NSTX active stabilization experiments is computed for beta near the ideal wall limit. Advanced state-space control algorithms yield a factor of 2 power reduction assuming white noise while remaining robust with respect to variations in plasma beta.

In an effort to clarify the physics origin of the energy confinement time scaling law in H-mode plasmas, a new analysis method is first proposed where the stored energy is separated into two parts-one coming from the marginal stability with the pedestal boundary condition and the other related to the turbulent dynamics. The method is then applied for the analysis of the global scaling law, as initial examples, focusing on the four parameters of plasma current, input power, magnetic field and density in the KSTAR-type tokamak model. It is shown that the method can provide more quantitative and explicit information on how various physics elements, such as the linear stability, nonlinear turbulent dynamics and pedestal boundary, contribute to the global scaling factor. While this method is not directly applicable, the L-mode is also considered for comparison, trying to clarify how a difference in the scaling law can occur between the H-and L-modes.

No abstract