Study on toroidal current plasmas from RFP to tokamak

扭曲磁力线结构普遍存在于各种空间等离子体、天体物理等离子体和实验室等离子体中，它们在这些系统的非线性动力学中起着至关重要的作用。磁通绳的产生就是这种空间现象的一个重要例子。磁重联产生具有螺旋磁力线的磁通管，这些磁通管在一段时间内保持稳定。磁场的结构变化伴随着能量的传递和转换，而磁能的驰豫导致等离子体粒子的加热，本研究计划在实验室等离子体实验的基础上，探索最常见的结构中“扭曲磁力线”的非线性动力学。利用两个环形实验，RESPOTE-1(东京大学)和EXXP-T2(阿尔芬实验室)，我们在ULQ和RFP区域产生了高温等离子体。与其他实验室系统相比，我们的实验的一个独特之处在于，Magneti…的扭曲更多的C场线相当紧张。高音高的磁场具有很大的自由能，可以激发扭转磁波动。在我们的实验中，我们观察到了磁涨落产生的强烈的非线性效应的明显迹象，我们称之为MHD弛豫。MHD弛豫中的能量耗散应该比平均电流的阻性耗散快得多。后者导致等离子体在长时间尺度上处于扩散状态。在较短的时间尺度内，会出现不同的准稳态。这种准稳态的分叉是一种典型的结构通过涨落的“自组织”。“耗散结构”的最本质特征是能量耗散增强，表现为等离子体的异常加热。粘性耗散加热离子，而阻性耗散加热电子。我们在平行于磁力线的方向上观察到了择优离子加热。这与自组织过程中离子粘性耗散的理论预测是一致的。因此，现在建立了与自组织相关的离子加热的微观机制。较少

Twisted magnetic-field-line structures appear commonly in many different space, astrophysical and laboratory plasmas, and they play an essential role in nonlinear dynamics of these systems. The creation of a magnetic flux rope is an important example of such space phenomena. Magnetic reconnection produce flux tubes with helicalmagnetic-field lines, which stay stable for a period of time. Structural change of the magnetic field is accompanied by energy transfer and transformation, and the relaxation of the magnetic energy results in heating of plasma particles.This research project was planed to explore, based on laboratory plasma experiments, the nonlinear dynamics of "twisted magnetic-field lines" in their most common structure. Using two toroidal experiments, REPUTE-1 (Univ.Tokyo) and EXTRAP-T2 (Alfven Lab.), we produced high-temperature plasmas in the ULQ and RFP regimes. A unique feature of our experiment, in comparison with other laboratory systems, is in that the twist of magneti … More c-field lines is rather tight. A high pitch magnetic field has a large free energy that can excite torsional magnetic fluctuations. In our experiments, we observe clear indications of strong nonlinear effects produced by magnetic fluctuations, which we call the MHD relaxation.The energy dissipation in the MHD relaxation should go much faster than that caused by the resistive dissipation of the mean current. The latter leads the plasma to a diffused state in a long time scale. A different quasi-steady state emerges within a shorter time scale. This bifurcation of a quasi-steady state in a typical "self-organization" of a structure through fluctuations. Enhanced energy dissipation, which is the most essential characteristic of a "dissipative structure", appears as anomalous heating of the plasma. The viscous dissipation heats ions, while the resistive dissipation heats electrons. We observe preferential ion heating in the direction parallel to the magnetic field lines. This observation is consistent to the theoretical prediction of ion viscous dissipation in the self-organization process. Hence, the microscopic mechanism of ion heating associated with the self-organization is now established. Less