Reversed Magnetic Shear Formation by RF

本研究的目的是通过局域射频电流驱动来控制等离子体输运和MHD活动。在本研究中，射频功率是在电子回旋波频率范围内通过注入微波来施加的。为了获得局部射频驱动电流，需要将微波波束聚焦到窄区。研制了微波功率传输系统，获得了非常窄的束斑(1.5 cm*2.2 cm)，与等离子体截面相比已经足够窄。该电流IRF的量通过环路电压的变化来监测。IRF与入射微波的方向有关，当微波的入射角度颠倒时，IRF的方向正好相反。IRF的最大值约为Loka，不到整个等离子体截面总等离子体电流的10%。然而，IRF被驱动在非常窄的区域，从而有效地改变了局域的磁组态。这一结果得到了以下事实的证实。当在与欧姆电流方向相反的磁轴区被分散时，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，导致了中心安全系数的增加。

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.