Presentation Gyrokinetic modeling issues of edge plasma

宮戸, 直亮

Tokamak edge turbulence plays an important role in determining fluxes towards a tokamak diverter which are critical for realization of fusion power stations. In particular, understanding the transition from a low confinement state (L-mode) to a high confinement state (H-mode) is one of critical issues. The gyrokinetic/gyrofluid models are the most sophisticated models for turbulence studies in magnetized plasmas, but the L-H transition has not been reproduced by the gyrokinetic/gyrofluid simulations so far. In the first place, the standard gyrokinetic model does not consider a fast flow (strong electric field) observed in H-mode plasmas and its applicability to edge plasmas is unclear. We have derived a guiding-center Lagrangian considering the fast flow. It is suitable for the L-H transition simulation because, in contrast to the conventional models for flowing plasmas, its symplectic part does not include a flow term as in the standard model. Its Hamiltonian has high-order flow terms including a cubic nonlinear term beyond the standard model in which a quadratic term is included. Measurements from a turbulence simulation with conventional tokamak L-mode edge parameters indicate that effects of the cubic nonlinear term are small and keeping the quadratic nonlinear term seems to be sufficient for tokamak edge simulations in a certain parameter regime.
18th International Congress on Plasma Physics

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