利用充气成像系统研究RMP控制ELM过程中边界湍流的结构演化及作用

Since the auxiliary heating power on EAST tokamak has been increased to more than 20 MW in 2014 due to the new NBI and ECRH systems and the upgrade of LHCD and ICRH systems, the high transient heat load from type-I ELM is a serious threat to the lifetime of PFC components, which is an obstacle to the achievement of long pulse H mode with high confinement. At present, it is a hot issue to study the ELM suppression by the technique of resonant magnetic perturbation (RMP). However, ELM suppression only occurs within limited operation ranges (q95, collisionality and density), and the mechanism remains unclear. As demonstrated by the DIII-D experiment, density fluctuations near the pedestal region react rapidly to the changing RMP magnetic field, and the turbulence increases significantly. A possible mechanism is that RMPs may damp zonal flows and thereby cause an increase in turbulence and transport. The dual gas puff imaging (GPI) diagnostic system has been installed on EAST in 2012 to investigate the 2-dimension structure and evolution of edge turbulence. The birth and propagation of edge turbulence (ELM filament) during the process of ELM suppression by RMP can be studied with the GPI diagnostics and reciprocating probes at midplane on EAST. The characteristics (structure, evolution and velocity) of edge turbulence and the interaction between zonal flow and turbulence will be investigated in our experiment, which will contribute to revealing the mechanisms mediating the interaction between RMP fileds and local transport. The development of a new nozzle of GPI diagnostics with a longer penetration length in plasma and a smaller amount of gas puff expands the GPI view area towards the pedestal region, providing more important information about edge turbulence for EAST tokamak. The active control of ELM with RMP in EAST could provide valuable reference to the steady state operation with high confinement in ITER and future fusion reactors.

随着EAST辅助加热功率大幅增加，I型边界局域模（ELM）导致的靶板超高瞬态热负荷严重威胁材料的寿命。利用共振磁扰动（RMP）线圈控制ELM是国际上的研究热点，实验发现完全抑制ELM时等离子体参数（q95、碰撞率和密度）要满足非常严格的条件，其中的机制还不清楚。DIII-D的实验发现台基区附近的湍流能快速响应RMP磁场变化，在RMP作用下大幅增长，可能是RMP抑制了带状流，引起湍流和等离子体输运的增加。EAST上的两套充气成像系统（GPI）能观测二维空间内边界湍流的结构和演化，结合快动探针系统，研究EAST上RMP控制ELM过程中边界湍流（包括ELM filament）的产生和演化，包括湍流的基本特征、结构、运动速度、以及湍流和带状流的相互作用，揭示边界湍流调节RMP磁场和局域等离子体输运的物理机制，可为主动控制ELM进而实现ITER和未来聚变反应堆的高参数稳态运行提供极有意义的参考。

研究了EAST共振磁扰动线圈（RMP）控制边界局域模（ELM）过程中的边界湍流输运及偏滤器靶板热流行为，RMP加入之后ELM得到有效抑制，SOL背景湍流大幅增强，同时湍流驱动的向外粒子通量也增加了约5倍，因此在H_α谱线和靶板饱和粒子流的本底均显著增大，且偏滤器靶板形成多条带状粒子流，缓减了主打击点热流。这表明在RMP作用下边界径向输运大幅增强，形成了粒子排出通道，能够稳定抑制ELM，控制偏滤器靶板热负荷。为了深入研究偏滤器靶板热负荷的沉积行为，我们对低杂波引起的三维偏滤器粒子流沉积效应进行了系统研究，结合包含了SOL螺旋电流丝的磁力线追踪程序，发现带状峰值热流到偏滤器打击点的距离与边界磁力线倾斜角吻合。实验上发现带状粒子流和原始打击点处的粒子流之比随着低杂波功率增加而增加。在I类和III类ELM的热流不对称性研究中，顺时针纵场时ELM爆发时内靶板的粒子流增加比外靶板要更显著，而在逆时针纵场时ELM爆发带来的粒子流更多沉积在外靶板，结合高低场侧快动探针测量的平行流，发现平行流主导了粒子流的SOL输运和靶板的内外不对称性。为了研究偏滤器靶板热流沉积宽度，我们利用SOLPS程序结合EAST物理实验，发现磁力线连接长度在靶板热沉积宽度与等离子体电流成反比关系中起着主要作用。这些研究结果有助于EAST在长脉冲高性能运行时主动控制靶板热流沉积。在先进仿星器装置W7-X上，我们研究了边界湍流输运与磁拓扑结构的关系。在限制器位形的实验中，较高加热功率条件下会激发一支约7kHz的电磁相干模，该模式在等离子体坐标系下沿着电子逆磁漂移方向传播，并呈现出对拓扑结构很强的依赖，即在磁岛内部磁力线连接长度大的区域该模式显著增长。在偏滤器实验中，最外闭合磁面外的磁岛附近出现了很强的湍动粒子通量区域，主要由80-120kHz的宽谱湍流驱动，很可能是密度梯度驱动的不稳定性引起的。对比研究EAST和W7-X上湍流输运与磁拓扑结构之间关系，对理解未来大型聚变装置边界输运有重要意义。此外，我们对EAST两套充气成像系统进行了升级改造。