Statistical Picture of hysteresis characteristics of transition phenomena in steady state current drive plasma

主要研究内容如下：在电流驱动等离子体中，研究了各种跃迁现象。首先，从滞后的角度研究了约束（等离子体存储能量/输入功率）和电流驱动效率（等离子体电流密度^★长半径/功率）的转变。发现存在一个功率阈值，在该阈值以上触发过渡。在转变时，离子和电子温度都增加，密度也增加。由于驱动电流增大，所以电流驱动效率提高。还研究了转移概率。驱动功率随时间变化，远大于限制时间，在阈值功率以下到阈值功率以上的跃迁特征称为前向跃迁。还研究了从高于阈值的“增强电流驱动”模式到低于阈值功率的L模式的后向跃迁。转移概率被定义为延迟 ...更多信息 转换相对于功率变化延迟的时间。研究了前向和后向跃迁的跃迁概率，发现前向和后向跃迁之间存在一个临界差，这个临界差导致了电流驱动的迟滞。其次，研究了双向低杂波电流驱动工作时电流驱动特性的跃迁。在实验中，前向LHW和后向LHW叠加，并研究了驱动电流的方向性。即，正向电流由FW LHW驱动，而反向电流由BW LHW驱动。实验结果表明，电流方向性从BW方向到FW方向的转变是BW/FW功率比的函数。当该功率比超过临界值10.8时，触发该转换。结果表明，当BW-LHW叠加且功率比超过临界值时，电流密度分布变窄，然后电流密度分布由中心峰值突然转变为宽峰值。第三，从等离子体与壁面相互作用的角度研究了长脉冲放电中的相变现象。首次发现了极低频振荡。这被称为ULF事件。在长脉冲操作中，有几个过程支配放电特性。输入射频功率通过射频天线前面的隧道过程从外板侧发射。射频耦合到等离子体强烈地依赖于该区域的密度梯度。在长脉冲放电过程中，来自等离子体和逃逸的高能电子的热负荷沉积在壁和天线上。表面温度升高改变了面向等离子体的部件的壁泵浦特性。因此，边缘或SOL密度可以在放电中变化。然后，这种扰动改变了耦合的减少或反射功率的增加。在ULF事件期间发生转换，然后终止五小时放电。热负荷和粒子扰动从环周围的主导PFC（轨道限制器）迅速增长，最终导致放电崩溃。相关的事件是由逃逸的高能电子引起的热点形成。用红外光谱仪测量了热斑上的局部温度。研究了氢的巴耳末带和福尔歇带随表面温度的变化。结果表明，当热斑温度超过临界值2100 K时，两条谱线都开始非线性增长，并随温度的升高而急剧增加，甚至在温度继续升高时发生翻转，最后在较低温度时衰减到原来的水平.少

The summary of this research is as follows.In the current drive plasma, various transition phenomena have been investigated. Firstly, the transition for the confinement (∝ plasma stored energy/input power) and current drive efficiency (∝ current^★density^★major radius/power) is studied with view point of hysteresis. It is found that there exists a power threshold above which a transition is triggered. At the transition, both ion and electron temperature are increased and the density is also increased. Since driven current is raised, current drive efficiency is enhanced. The transition probability is also studied. The driven power is varied with a time, much longer than the confinement time, and the transition characteristics below the threshold power to above it, called forward-transition. Backward- transition is also studied from the "Enhanced current drive" mode achieved above the threshold down to the L-mode below the threshold power. The transition probability is defined as a delay … More time with which a transition is delayed with respect to a change in power. This transition probability is studied for both forward and backward transitions, and it is found that there is a critical difference between then and this difference leads to a hysteresis.Secondly, a transition in current drive property is studied for bi-directional lower hybrid current drive operation. In this experiments, the forward LHW and backward LHW are superposed and the directivity of the driven current is studied. Namely, the forward current is driven by FW LHW, but the backward current is driven by the BW LHW. The experiments show that a transition of the current directivity from the BW direction to FW direction as a function of the BW/FW power ratio. This transition is triggered when this power ratio exceeds a critical value of 〜 0.8. It is found that the current density profile becomes narrow when the BW-LHW is superposed and the power ratio exceeds above the critical one, and then the transition of the current profile changes from the centrally peaked to a broad one suddenly. A hysteresis is not taken for this experiments.Thirdly, a transition is studied in a long pulse discharge from a view points of plasma wall interaction. Oscillations at the very low frequency are found for the first time. This is called ULF events. In the long pulse operation, there are several processes which dominate discharge characteristics. The input rf power is launched from the out board side via a tunneling process in front of the rf antenna. The rf coupling to the plasma depends strongly on the density gradient in this region. During the long pulse discharge, the heat load from the plasma and escaped energetic electrons are deposited on the wall and antenna. The surface temperature rise changes the wall pumping property of the plasma facing components. Thus the edge or SOL density may vary in the discharge. Then this perturbation changes the reduction of the coupling or increment in the reflected power. A transition occurs during the ULF event, and then the five hour discharge is terminated. The heat load and particle perturbation grow rapidly from the dominant PFC (rail limiter) around the torus and finally they collapse the discharge. The related events are hot spot formation which may caused by the escaped energetic electrons. The local temperature on the hot spot is measured with the IR spectrometer. The hydrogen Balmer and Faulcher band are studied as a function of the surface temperature. It is found that both emission lines start to increase non-linearly as the hot spot temperature exceeds a critical values of 〜2100 K and they are sharply increased with increasing temperature and turns over even when the temperature still increases, and finally they decay to the previous level at the lower temperature. Less