Study of Toroidal Currents and MHD Equilibrium in LHD Experiment
Study of Toroidal Currents and MHD Equilibrium in LHD Experiment
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LHD实验中环形电流和MHD平衡的研究
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通讯作者：
Ida K.. Kaneko
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作者：
Ida K.. Kaneko
1.在螺旋装置中，不需要净环向电流来产生等离子体约束磁场。然而，理论预测表明，有几种非电感环形电流，如自举电流、大川电流和微波驱动电流。这些环形电流不够大，不足以激活电流驱动的不稳定性。然而，它们有可能通过改变磁结构来影响MHD的稳定性和输运。方向增加旋转变换的环向电流，我们称之为共向电流，导致磁切变的减小和沙弗拉诺夫位移的抑制，抑制了磁井的形成。由于新经典纹波输运，它改善了粒子约束，而交换模式不稳定[1,2]。磁切变的减弱也可能导致磁岛的延伸。在LHD的NBI等离子体中观察到超过100kA的净环向电流。基于自举电流和大川电流的理论模型，分析了NBI氢气放电中环形电流的时间演化，确定了电流驱动机理。
1.Introduction In helical devices, net toroidal currents aren't necessary to produce magnetic field for plasma confinement. However, theoretical prediction suggests that there are several kinds of non-inductive toroidal currents, for example, bootstrap currents, Ohkawa currents and microwave driven currents. These toroidal currents aren't large enough to activate current driven instabilities. However, there is a possibility that they can affect the MHD stability and transport through changing of the magnetic configurations. The toroidal currents with direction increasing the rotational transform, we call co-direction, lead to the decrease in the magnetic shear and the suppression of Shafranov shift which restrains the formation of magnetic well. And it improves the particle confinement due to neoclassical ripple transport, while interchange mode is destabilized[1,2]. The reduction of magnetic shear may lead to extension of magnetic island, too. Net toroidal currents of over 100kA have been observed in NBI plasmas of LHD. We have analyzed the time evolution of toroidal currents in NBI hydrogen discharges in order to identify the current driven mechanism based on the theoretical model of bootstrap current and Ohkawa current.