托卡马克中小幅度边缘局域模的形成机制研究

How to avoid the excessively high heat load caused by the giant edge localized modes (ELMs) with high confinement has become one of the urgent problem in magnetic confinement fusion. H-mode operation with small ELMs achieved by active external control or plasma optimization is one of the possible solution. However, there are a lot of uncertainties to obtain small ELMy H-modes, since it is unclear for understanding the small ELMs. In this project, we would conduct experiments in EAST superconducting tokamak. By using the edge Thomson Scattering system, edge probe system, gas puff imaging, beam emission spectrum systems, microwave reflctometry and other edge/pedestal diagnostics with high spatial and temporal resolution, accompanying with several simulation codes, i.e., BOUT++, ELITE and so on, we would study the dynamics of the small ELMs in the EAST long-pulse high-confinement plasmas. We focus on the profile evolution and the interaction among the edge fluctuations (edge coherent modes and turbulence), edge pressure gradient and shear flow. Based on these, we explore the formation and resulted transport of the small ELMs. The research ouput of this project could provide useful reference of small ELMy H-mode scenario for the achievement of steady-state long-pulse operation in ITER and future fusion reactor.

如何在维持高约束状态下，避免大幅度边缘局域模带来的超高瞬态热负荷是目前磁约束聚变研究亟需解决的关键科学问题。采用自发产生的或者主动控制获得的伴随小幅度边缘局域模的H模运行模式是可能的解决方案。但是，目前获得小幅度边缘局域模的H模运行方案仍存在不确定性，这很大程度上是因为我们对小幅度边缘局域模的物理机制仍然不清楚。本项目将依托EAST超导托卡马克装置，使用边界汤姆逊散射系统、边界探针、充气成像系统、束发射光谱、微波反射仪等高时空分辨边界诊断，结合多种模拟程序，研究EAST长脉冲高约束等离子体中小幅度边缘局域模的动力学行为，包括边界参数演化、边界涨落（湍流和准相干模等）和压强梯度与剪切流的相互作用等，探索小幅度边缘局域模的形成机制和输运行为，为获得带有小幅度边缘局域模的H模等离子体并进而实现ITER和未来聚变反应堆的高参数稳态运行提供参考。

在EAST射频波和中性束加热和锂化壁处理条件下，获得了脉冲长度超过15秒的完全非感应稳态小/无ELM高约束运行模式。实验分析了小/无ELM运行模式的主要运行区间，并发现在高碰撞率的小/无ELM放电时，边界准相干模带来有效的粒子和热输运从而有利于小/无ELM H模的获得。提高加热功率，一支磁涨落分量强静电涨落弱的磁相干模将取代ECM影响台基不稳定性。而在更低的碰撞率条件下，模拟研究发现台基附近有理面的E×B流剪切来改变边界模结构从而影响ELM运行模式。借助EAST托卡马克上不断发展完善的诊断测量系统，利用MHD模拟程序进行动理学平衡计算以及台基线性稳定性分析，发现长脉冲小/无ELM H模放电的台基位于剥离-气球模稳定区间，不稳定性增长率和临界稳定压力小于第一类ELM台基。通过与DIII-D的合作发现，偏滤器几何结构和封闭性也能够通过影响台基区的加料，从而深刻影响台基宽度和台基分化，并影响不稳定性边界，进而影响ELM的特征。这些结果都能为下一阶段EAST高约束准稳态等离子体的获得提供参考。