Reversed Magnetic Shear Formation by RF

本研究的目的是通过局部射频电流驱动来控制等离子体输运和MHD活性。在本研究中，射频功率是通过在电子回旋波的频率范围内注入微波来施加的。为了获得局部的射频驱动电流，需要将微波束聚焦到狭窄的区域。研制了微波功率传输系统，获得了较窄的光束光斑（1.5cm * 2.2cm），与等离子体截面相比已经足够窄。将微波注入等离子体，产生射频驱动电流。通过回路电压的变化来监测电流IRF的量。红外辐射场依赖于入射微波的方向，当微波注入角反转时，红外辐射场的方向相反。IRF的最大值约为lOkA，小于整个等离子体截面总电流的10%。然而，由于IRF是在狭窄的区域内驱动的，因此它可以有效地改变局部的磁结构。结果被以下事实所证实。当与欧姆电流相反方向驱动在磁轴区域时，锯齿不稳定性被抑制。结果表明，反向射频电流驱动降低了中心区域的电流密度，导致中心安全系数增大。

The purpose of this investigation is to control the plasma transport and MHD activity by local RF current drive, In this investigation, RF power is applied by the injection of microwave in the frequency range of electron cyclotron wave. In order to get local RF-driven current, it is necessary to focus the microwave beam into narrow region. Microwave power transmission system was developed and we obtained quite narrow beam spot ( 1.5cm * 2.2cm), which is sufficiently narrow compared with plasma cross section.When microwave is injected into plasma, RF-driven current was generated. The amount of this current IRF was monitored by the change in the loop voltage. IRF IRF was dependent on the direction of incident microwave, Further, the direction of IRF was opposite when the injection angle of microwave was reversed. Maximum value of IRF was about lOkA, which was less than 10% of total plasma current across the whole plasma cross section. However, IRF was drive in so narrow region that it changed the local magnetic configuration efficiently. The result was confirmed by the following facts. When was dirven on the magnetic axis region in the inverse direction of Ohmic current, sawthooth instability was suppressed. The result showed that inverse RF current drive reduced the current density of the central region, resulting in the increase of the central safety factor.