DC HELICITY INJECTION AND MHD RELAXATION STUDIES IN AN RFP BY MAKING USE OF INSULATED SEGMENTS OF DISCHARGE CHAMBER

本研究的目的之一是利用STE-2反应堆放电室的绝缘段来探索在反应堆中采用直流螺旋度注入方案的可能性，另一个目标是研究与螺旋度注入相关的磁流体驰豫过程。在STE-2上用标准RFP和超低Q(ULQ)等离子体进行的实验结果如下：(1)在边缘插入金属电极进行直流螺旋度注入。电极由比表面积为0.8cm2的不锈钢制成。这两个电极插入在相同的环形位置，极向相隔270ﾟ。施加的最大电压为400V，电流为100A，注入电流密度大致等于平均环向电流密度。在电极附近观察到环向磁通量略有增加(5%)。这种环面局域通量增加并不依赖于Pola…更多的施加电压，这与基于螺旋度平衡关系的预期相矛盾。无论是在边缘极向场还是在边缘环向场，都没有观察到明显的增加。结果表明，局域焦耳加热引起的局部β值的增加在等离子体响应中起着重要作用。(2)直流螺旋度注入是通过在电离室的绝缘段之间施加电压，同时通过空间调制环状场来产生穿透这些段的磁通来实现的。由于环向场调制对RFP放电的不利影响，该方法仅适用于中电流(20kA)ULQ等离子体。在1.3kV的外加电压下，在腔体极向间隙处测得的等离子体电流增加了20%。在局部导电壳的帮助下，通过减小间隙处的场误差，进一步优化了RFP放电。新方案的直流螺旋度注入将应用于改进的RFP放电。较少

It is one of the objectives of this research project to search for the possibility of DC helicity injection scheme in an RFP by taking advantage of the insulated segments of the discharge chamder of the STE-2 RFP.The other includes the MHD relaxation process associated with the helicity injection. Experiments in STE-2 with standard RFP and ultra-low-q (ULQ) plasmas have provided the following results.(1) DC helicity injection was performed with the use of metal electrodes inserted at the edge. The electrodes were made of stainlewss steel with surface area of 0.8 cm2. These two electrodes were inserted at the same toroidal location, separated by 270ﾟ poloidally. The maximum voltage applied was 400 V with a current a current of 100 A.The injected current density was roughly equal to the average toroidal current density. A slight (5 %) increase of the toroidal magnetic flux was observed in the vicinity of the electrodes. This toroidally localized flux increase did not depend upon the pola … More rity of the applied voltage, which was contradictory to the expectation based on the helicity balance relation. No appreciable increase was observed either in the edge poloidal field or in the edge toroidal field. The results may indicate that increased local beta value due to localized Joule heatinh plays important role in plasma response.(2) DC helicity injection was made by applying voltage between the insulated segments of the chamber and simultaneously by spatially modulating the toroidal field so as to produce the magnetic flux penetrating these segments. This method was applied only to medium-current (20 kA) ULQ plasmas because of the deleterious effect of the toroidal field modulation on RFP discharges. The plasma current measured at the chamber poloidal gap has increased by 20 % with the applied voltage of 1.3 kV.A further optimization of RFP discharge is in progress by reducing field errors at the gap with the help of localized conducting shell. The new scheme DC helicity injection will be applied to the improved RFP discharges. Less