| Research Abstract |
Controlling anomalous transport arising from plasma turbulence is a great challenge for the development of magnetically confined fusion devices such as tokamaks. It is of significant importance to understand the relation of turbulence and plasma flows as flows in plasmas such as zonal flows are known to suppress turbulence under high-confinement mode operations of such fusion devices. In this work, we have clarified how electromagnetic turbulence can contribute to the formation of zonal flows through stabilization of Kelvin-Helmholtz instabilities. In 2001, we focused on resistive drift-Alfven waves and resistive wall modes and performed nonlinear numerical simulations of these modes. It is found that, although the magnetic fluctuation energy due to drift Alfven modes is relatively small compared with its kinetic energy, the Maxwell stress reduces the Reynolds stress, inhibiting the formation of poloidal flows. Also we have found that, if a resistive wall is sufficiently close to the p
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lasma and the growth rate of resistive wall mode is finite, the Maxwell stress due to magnetic fluctuations diminishes poloidal flows and the flow velocities near rational surfaces become almost zero. In 2002, we focused on the resistive interchange mode (RIM) and obtained the following results
1) In the case where two resonant surfaces exist in the plasma (i.e., the case of double resonance), poloidal shear flows due to fluctuations are formed at the positions of mode resonant surfaces and the minimum rotational transform. On the other hand, in the case of non resonance, a flow is formed at the position of the minimum rotational transform
2) In the case of single resonance, nonlinear interactions of RIMs form a locally flat or even inverse-gradient density profile near the rational surfaces, which results in a density profile stable even under high-β conditions
3) The poloidal shear flows arising from fluctuations further localize the flat or inverse-gradient region in the density profile Less
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