トカマクにおける電流分布の多様性 : 電流ホール配位の形成機と構閉じ込め特性

概要

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The formation mechanism of the current hole in tokamak plasmas is reviewed. Experimental results of JT-60U are shown. Increase of the off-central noninductive current is a key factor for the current-hole formation. The internal Transport Barrier (ITB), which generates large bootstrap current, plays an important role. The central current density in the hole stays nearly 0. The idea of a new equilibrium for a tokamak plasma with a current hole is introduced. This equilibrium configuration called ”Axisymmetric Tri-Magnetic-Islands(ATMI) equilibrium”, has three islands along the R direction (a central-negative-current island and side-positive-current islands). The equilibrium is stable with the elongation coils when the current in the ATMI region is limited to a small amount. The confinement properties of a current-hole configuration withbox-type ITB is described. A scaling of the core poloidal beta inside the ITB, βp,core is given as εfβp,core ≈ 1,which suggests the equilibrium limit (εf : inverse aspect ratio at the ITB foot). Though the core stored energy is little dependent on the heating power, the estimated heat diffusivity in the ITB region moderately correlates with a neoclassical diffusivity.
2003-11-25