EAST低杂波电流驱动的数值模拟及分析

Simulation and analysis of lower hybrid current drive on EAST tokamak

介绍了波的射线轨迹程序C3PO和求解三维Fokker-Planck方程程序LUKE的基本计算过程及其物理机制。该程序采用的是反弹平均方法,考虑了相对论效应和捕获粒子效应。利用此程序模拟并分析了EAST偏滤器位形下等离子体电流对低杂波传播以及驱动效率的影响。计算结果表明,随着电流的增大,低杂波射线轨迹在极向的旋转加快,功率沉积位置内移,驱动效率变大。此外,还发现当波束在上平面边界反射回来向等离子体中心传播时,平行折射率有较大的上移。考虑快电子的径向扩散后,驱动电流分布变宽。横越边界的损失以及一部分快电子因扩散到碰撞增强的区域而迅速慢化导致驱动效率下降。当扩散系数为1.5m2?s?1时,驱动电流的模拟值和实验值基本吻合。

The calculation processes and consideration on the physical regime of C3PO, a ray-tracing code, and LUKE, a fast numerical solver for the 3-D Fokker-Planck equation, are presented. Bounce average is used and the relativistic and particle-trapped effects are taken into account in the codes. The simulation and analysis of plasma current influence on rays propagation and current drive （CD） efficiency in EAST divertor configuration have been carded out using these codes. The numerical results indicate that, with the increase of plasma current, the rotation of the poloidal rays trajectory becomes faster, the power deposition profile shifts on axis, and the CD efficiency becomes higher. In addition, it is discovered that the trajectory provided high Nll-upshift when the ray propagated towards the edge density cut-off at the top of the chamber and then bounced back towards the plasma centre. When the effect of radial diffusion of fast electrons is considered, the shape of driven current becomes broad, but CD efficiency decreases due to the radial loss and collisional loss of electrons moving to the region where collision is serious. While the diffusion coefficient is assumed to be 1.5m2-s-1, the modeling result of driven current approaches to the experimental value.