Current drive by lower hybrid waves that have a phase velocity five times the electron thermal velocity has been investigated in the JFT-2M tokamak. Two different modes of tokamak operation, the automatic current regulation (ACR) and the automatic voltage regulation (AVR) modes, were employed to study the plasma control during the current drive. In the ACR mode, which is the ordinary tokamak operation in JFT-2M, the current of the poloidal-field coils which produce the main magnetic flux outside the torus is controlled by thyristor power supplies, while in the AVR mode their voltage is controlled. The results indicate that control of the poloidal field determines the time evolution of the plasma current during current drive whereas operation in the AVR mode suggests the sustainment of a steady-state plasma current through recharging of the Ohmic transformer. A high current drive efficiency was obtained which increased with the plasma current as up to Ip = 150 kA. The dependence of the current drive efficiency on the plasma current is related to the electron temperature and to propagation effects of the lower hybrid waves. The interaction of the excited lower hybrid waves with the electrons was investigated by pulse height analysis of the soft-X-ray emission. It was shown that the measured soft-X-ray energy spectrum is consistent with the theoretical spectrum of the launcher. The characteristic times for the modification of the electron distribution function and for the drop in loop voltage are proportional to the electron density.
已在JFT-2M托卡马克装置中研究了相速度为电子热速度五倍的低混杂波电流驱动。实验中采用了两种托卡马克运行模式，即自动电流调节（ACR）模式和自动电压调节（AVR）模式，以研究电流驱动过程中的等离子体控制。在ACR模式下，即JFT-2M的常规托卡马克运行方式，产生环外主磁通的极向场线圈电流由晶闸管电源控制，而在AVR模式下则控制其电压。结果表明，极向场的控制决定了电流驱动过程中等离子体电流的时间演化，而AVR模式下的运行则表明通过欧姆变压器再充电可实现稳态等离子体电流的维持。获得了高电流驱动效率，该效率随等离子体电流增大而提高，最高可达Ip = 150 kA。电流驱动效率对等离子体电流的依赖关系与电子温度以及低混杂波的传播效应有关。通过脉冲高度分析对软X射线发射进行了研究，以考察激发态低混杂波与电子的相互作用。结果表明，测得的软X射线能谱与发射体的理论能谱一致。电子分布函数发生修正的特征时间以及环路电压下降的特征时间均与电子密度成正比。