1.School of Nuclear Science and Technology, University of South China, Hengyang 421001, China 2.Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, China 3.Department of Engineering and Applied Physics, University of Science and Technology of China, Hefei 230026, China 4.School of Electrical Engineering, University of South China, Hengyang 421001, China
Abstract:Rotation and its shear can reduce the magnetohydrodynamic instabilities and enhance the confinement. The LHCD has been proposed as a possible means of rotation driving on a future fusion reactor. Exploring the mechanisms of LHCD rotation driving on the current tokamaks can provide important reference for future reactors. On EAST, it was previously shown that 2.45 GHz LHCD can drive plasma toroidal rotation and the change of edge plasma rotation leads the co-current core rotation to increase. At higher frequency, 4.6 GHz lower hybrid wave can more effectively drive co-current plasma toroidal rotation. On EAST, at the lower current, the effects of different LHCD power on plasma toroidal rotation are analyzed. Higher power LHCD has a better driving efficiency. The effect of safety factor (q) profile on toroidal rotation is also presented. The LHCD can change the profile of safety factor due to current drive. It is found that when the power exceeds 1.4MW, the q profile remains unchanged and the rotation changes only very slightly with LHCD power, suggesting that the current profile is closely related to rotation. In order to further analyze the dynamic process of plasma toroidal rotation driven by lower hybrid current drive on EAST, the toroidal momentum transport due to LHCD is deduced by using the modulated LHCD power injection. Based on the momentum balance equation, the toroidal momentum diffusion coefficient (χφ) and the toroidal momentum pinch coefficient (Vpinch) are obtained by the method of separation of variables and Fourier analysis for the region where the external momentum source can be ignored. It is found that the momentum diffusion coefficient (χφ) and momentum pinch coefficient (Vpinch) tend to increase from the core to the outer region. This is consistent with the characteristic that the toroidal rotation velocity first changes in the outer region and then propagates to the core when the toroidal rotation is driven by LHCD. Keywords:lower hybrid current drive/ toroidal rotation velocity/ safety factor/ toroidal momentum transport
其中$ m_{\rm i}, n_{\rm i}, M, S $和Vt分别为离子质量、粒子密度、环向动量的径向通量、环向动量源和环向旋转速度. 如图5(c)所示, 可以用正弦函数对环向速度进行拟合, 则环向速度Vt的扰动展开形式为 图 5 典型参数随时间变化的波形图 (a) 电子温度; (b) 离子温度; (c) 环向旋转速度对调制束的响应; (d) LHCD功率(黑色)和芯部弦平均电子密度(蓝色) Figure5. Waveforms of typical parameters: (a) Electron temperature; (b) ion temperature; (c) toroidal rotation velocity; (d) LHCD power (black) and central line averaged electron density (blue).
图 1 典型参数随时间变化的波形图 (#70938) (a) 等离子体电流 (黑色), 低杂波功率 (蓝色); (b) 环电压 (黑色)和内感 (蓝色); (c) 芯部弦平均电子密度; (d) 储能; (e) 芯部电子温度 (黑色)和芯部离子温度 (红色); (f) 芯部环向速度变化
图 2 不同低杂波功率下典型参数随时间变化的波形图 (a) 等离子体电流; (b) 芯部弦平均电子密度; (c) 低杂波功率; (d) 芯部环向旋转速度变化
图 3 低杂波功率与芯部环向旋转速度变化关系
图 4 不同低杂波驱动功率下安全因子剖面
图 5 典型参数随时间变化的波形图 (a) 电子温度; (b) 离子温度; (c) 环向旋转速度对调制束的响应; (d) LHCD功率(黑色)和芯部弦平均电子密度(蓝色)
图 6 (a) 环向速度调制幅度(Vt0)的剖面图; (b) 环向速度相位变换(φ)的剖面图
图 7 (a) 环向动量扩散系数(χφ) 的剖面图; (b) 箍缩系数(Vpinch)的剖面图