Self-Orgamzation in Low-Aspect Ratio Tens Plasma and Healing of Magnetic Chaos

在本研究项目中，我们建造了一台RFP机器RELAX，其纵横比（A）为2，是迄今为止世界上最低的值。经过一年多的运行，获得了最大等离子体电流<80 kA，最小放电电阻为1 mΩ，放电持续时间大于2 ms，RFP配置持续时间为L5-2 ms的放电参数。在平顶放电中，我们观察到两种类型的环形模式谱的m=1模式取决于放电阶段。在磁涨落水平最低的后一阶段，边缘磁涨落具有多螺旋（MH）态的特征，其核心共振模式主要为m=1/n= 4，5。在早期到中期阶段，已观察到低振幅（但高于后期阶段）单模（n=4或n=5）的周期性增长和衰减。在圆顶RFP放电中，m=1/n= 关于我们 4单主模在邻近模的抑制下呈准周期性增长，环形模谱具有准单螺旋度（QSH）特征，主模振幅高于其他RFP实验。这些观测结果与低ARFP平衡剖面的理论预测一致。在RELAX中，自反转模式操作也成为可能，其放电的特征在于磁场分布的大规模变化。测量的非对称分量的轮廓与螺旋欧姆平衡（HOE），其中RFP配置是维持没有磁混沌的那些符合得很好。所测量的振荡可以是HOE配置的环形旋转的指示。开发了一个新的平衡重构程序RELAXFit。我们已经将MSTFit代码的操作制度扩展到较低的A制度。这项工作是作为美日核聚变合作计划的一部分进行的。在RELAXFit中，我们考虑了新古典效应，以估计RELAX中的自举电流。在整个研究项目中，我们已经建立了低A RFP配置，环形等离子体的新制度的进一步实验研究的基础。少

In this research project, we have constructed an RFP machine RELAX, whose aspect ratio (A) is 2, the world's lowest value to date. During its 1st phase operation for about a year the following discharge parameters have been achieved: maximum plasma current of <80kA, minimum discharge resistance of 1 mΩ discharge duration longer than 2 ms with RFP configuration sustained for L5-2 ms. The MHD characteristics of low-ARFP plasmas can be summarizes as follows. In flat-topped discharges, we have observed two types of toroidal mode spectrum of the m=1 modes depending upon the discharge phases. In the later phase, where the magnetic fluctuation level tends to be the lowest, the edge magnetic fluctuation has a characteristic of multi-helicity (MH) state with dominant core resonant m=1/n=4,5 modes. In the early to mid phase, periodic growth and decay of a low-amplitude (but higher than in the later phase) single mode, either n=4 or n=5, has been observed. In round-topped RFP discharges, a m=1/n= … More 4 single dominant mode tends to grow quasi-periodically with suppression of the neighboring modes, and the toroidal mode spectrum has the quasi-single helicity (QSH) characteristic with dominant mode amplitude higher than in other RFP experiments. These observations are in agreement with theoretical predictions from low-ARFP equilibrium profiles. In RELAX, the self-reversal mode operation has also become possible, which discharge is characterized by a large-scale change in magnetic field profile. The measured profiles of asymmetric components are in good agreement with those of Helical Ohmic Equilibrium (HOE), in which RFP configuration is sustained without magnetic chaos. The measured oscillation may be an indication of toroidal rotation of the HOE configuration. A new equilibrium reconstruction code, RELAXFit, has been developed. We have extended the operation regime of the MSTFit code to the lower-A regime. This work has been performed as a part of US-Japan Fusion Collaboration Program. In the RELAXFit, we have taken into account the neoclassical effect in order to estimate the bootstrap current in RELAX. Throughout this research project, we have established the basis for further experimental study of low-A RFP configuration, a new regime of toroidal plasmas. Less