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

本研究项目的目标之一是利用STE-2 RFP放电模的绝缘段，在RFP中寻找直流螺旋注入方案的可能性。另一个包括与螺旋注入相关的MHD松弛过程。STE-2中标准RFP和超低q （ULQ）等离子体的实验提供了以下结果。(1)采用边缘插入金属电极进行直流螺旋注射。电极由不锈钢制成，表面积为0.8 cm2。这两个电极被插入在相同的环面位置，并以270个极点分开。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面电流密度。在电极附近观察到环形磁通量略有增加（5%）。这种环形局域磁通的增加不依赖于外加电压的极性，这与基于螺旋平衡关系的期望是矛盾的。在边缘极向场和边缘环向场中均未观察到明显的增加。结果表明，局域焦耳加热引起的局域β值升高在等离子体响应中起重要作用。(2)直流螺旋注入是通过在腔室的绝缘段之间施加电压，同时对环形场进行空间调制，从而产生穿透这些绝缘段的磁通。由于环形场调制对RFP放电的有害影响，该方法仅适用于中电流（20 kA） ULQ等离子体。当施加电压为1.3 kV时，在腔室极向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，通过减少间隙处的场误差，进一步优化RFP放电正在进行中。新方案直流螺旋注入将应用于改进的RFP放电。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