EAST三维场下台基湍流环向不对称性形成机理研究

The application of resonant magnetic perturbation (RMP) field has been demonstrated as a mechanism for suppressing edge localized modes (ELM) in various devices. ELMs have been suppressed successfully when pedestal electron density and global energy confinement almost unchanged with rotating 3D fields on EAST in recent experiment. The pedestal gradient region density is modulated by RMP current and pedestal gradient even larger than ELMy H-mode in some toroidally local place. The increasing of pedestal gradient is accompanied by a broadband turbulence, suggesting that both pedestal profile and turbulence are non-axisymmetric in plasma. Present simulation results and theory cannot give a detail description about the mechanism of this phenomenon. The broadband turbulence structure and behavior are still not clear either. So the main purpose of this project is focussed on pedestal turbulence structures and formation mechanism with 3D fields. All the experiments will be conducted on the EAST superconducting tokamak. Several pedestal diagnostics which locates at different equatorial plane ports will be utilized to provide provide simultaneous measurements of the time evolutions of pedestal fluctuations and profiles. Exploration of the broadband turbulence properties and the relations between turbulence variation and pedestal pressure gradients with 3D fields. The contribution of pedestal turbulence increasing to ELMs suppression also will be studied. The results of this project could provide valuable reference to RMP physics and active control ELMs on ITER in future.

共振磁扰动（RMP）场能有效的抑制边界局域模（ELM）已在多个装置上得到证实。EAST最近实验发现RMP对ELM实现很好抑制的同时，台基压力梯度沿环向不再是对称结构，在环向存在台基压力梯度大于ELMy H模的区域，同时伴有宽谱湍流的出现。但关于宽谱湍流的特征和形成机制目前仍不清楚，理论和模拟结果也不能给出很好的解释，需要通过开展相关实验进行深入研究。本项目拟利用多项沿EAST大环方向布置的高性能分布和涨落测量工具，开展三维场下台基湍流环向不对称性的实验研究，测量台基宽谱湍流的结构特征和演化规律，探究台基湍流不对称性和三维台基结构之间的依赖关系，进而揭示RMP影响台基湍流的机制。期望通过本项目的开展，加深对RMP相关物理的认知，为将来ITER更好的利用RMP控制边界局域模提供实验参考。

大尺度的边界局域模瞬间排出的大量粒子和热会严重侵蚀面向等离子体材料，给下一步磁约束聚变装置提出了极大的挑战。共振磁扰动线圈（RMP）能控制边界局域模已在国际上多个装置得到验证，并将应用于ITER。然而，湍流输运在RMP控制边界局域模和密度排出（pump-out）中所起到的作用至今仍不清楚。本项目利用EAST多样的湍流诊断工具，如锂束发射光谱，电子回旋辐射成像和多普勒背向散射等，发现在RMP工作期间台基湍流存在环向不对性。在n=1边界局域模被抑制条件下，等离子体没有发生可见的密度排出。边界等离子体密度和台基压力梯度受到RMP调制，台基湍流的频谱展宽和涨落幅度在环向上存在不对称性。湍流涨落幅度受到RMP环向模数的调制，湍流涨落幅度增强时伴随着台基压力梯度的下降，说明台基压力并不是湍流增强的诱因。进一步研究发现，宽谱湍流的形成伴随着较弱的电场剪切，湍流被抑制时台基梯度区剪切率明显增加，说明环向不对称的电场剪切可能是非轴对称的湍流形成的诱因，这为提高湍流输运进而抑制边界局域模和长脉冲稳态运行提供了研究方向。