Formation of Zonal flows and Kelvin-Helmholtz instabilities in magnetically confined plasmas

控制等离子体湍流引起的反常输运对于托卡马克等磁约束聚变装置的发展是一个巨大的挑战。了解湍流和等离子体流动的关系是非常重要的，因为等离子体中的流动，如带状流，在此类聚变装置的高约束模式操作下，可以抑制湍流。在这项工作中，我们阐明了电磁湍流如何通过稳定开尔文-亥姆霍兹不稳定来促进纬向流的形成。2001年，我们重点研究了阻性漂移-阿尔芬波和阻性壁模式，并对这些模式进行了非线性数值模拟。结果表明，虽然漂移Alfven模产生的磁涨落能量与其动能相比相对较小，但麦克斯韦应力降低了雷诺应力，抑制了极向流的形成。我们还发现，如果一面阻性墙足够靠近p…拉斯玛越大，阻性壁模的增长率就越小，磁涨落引起的麦克斯韦应力减小了极向流，有理面附近的流速几乎为零。2002年，我们对阻性交换模式(RIM)进行了研究，得到了以下结果：1)在等离子体中存在两个共振面的情况下(即双共振的情况)，在模式共振面和最小转动变换的位置形成了由涨落引起的极向剪切流。另一方面，在非共振的情况下，在最小旋转变换的位置处形成流动2)在单共振的情况下，轮缘之间的非线性相互作用在有理曲面附近形成局部平坦甚至逆梯度的密度分布，这导致即使在高β条件下密度分布也是稳定的3)由波动引起的极向剪切流进一步局部化密度分布中的平坦或逆梯度区域

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 … More 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 results1) 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 transform2) 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 conditions3) The poloidal shear flows arising from fluctuations further localize the flat or inverse-gradient region in the density profile Less