中空电子密度分布下的漂移波不稳定性

The inverted (i.e., a radially increasing) electron density profile appears in association with the pellet injection for core fueling or control of the edge localized mode (ELM) in tokamak plasmas. Actually, the inverted electron density profile sometimes appears spontaneously during the low to high confinement (L-H) mode transition. However, relatively limited studies are available in the literature on the drift wave characteristics in the inverted electron density profile case. The research of this project is helpful to understand the physical mechanism of turbulent transport and the control of drift instability, providing an important basis for improving the confinement performance of tokamak plasma. This project is based on the theoretical analysis and related experiments, and focuses on the properties of drift wave instabilities with scale length of electron and ion gyro-radius in tokamak plasmas with hollow electron density profile. The main contents are: gyro-kinetic model is used to derive the dispersion relation of the multiple modes in the collision and collisionless case with kinetic electron response; The effects of hollow electron density profile on the linear growth and mode coupling are discussed in detail by the numerical solution of dispersion relation; Based on the eigenvalue and initial nonlinear codes, we also calculate the dependence of mode structure as well as nonlinear evolution of the mode; Comparing the result of experiments, explore the means of controlling them, and to understand the basic behavior of plasma and the research on advanced operation scenarios. A possible implication of this work on particle transport in pellet fuelled tokamak plasmas is also discussed. This research activity can also be expected to lead to the identification of solutions by which inward turbulent transport can be maximized, or at least, outward turbulent transport can be minimized.

托卡马克聚变装置中，低约束模向高约束模转换以及利用弹丸注入加料、缓解边界局域模的过程会产生中空电子密度剖面，并由此触发漂移波不稳定性。然而，其物理机制及其性质并不清楚。该项目拟探索和掌握通过控制模式相互作用来改善等离子体参数，为在托卡马克高模式运行中进一步降低等离子体输运水平提供必要的理论依据。.本项目立足于理论分析并结合相关实验，重点研究中空电子密度剖面下电子与离子回旋尺度漂移波不稳定模式，主要研究内容有：.1.采用回旋动理学模型，推导线性碰撞/无碰撞漂移波不稳定性的色散关系；数值求解色散关系，明确中空电子密度对不稳定性线性增长的作用；.2.采用非线性程序，数值计算模式的本征结构对电子密度剖面的依赖关系及非线性特征；.3.通过与国内外实验结合，进一步解释密度剖面对漂移波不稳定性在不同实验条件下的作用机制。

托卡马克聚变装置中，低约束模向高约束模转换以及利用弹丸注入加料、缓解边界局域模的过程会产生中空电子密度剖面，并由此触发漂移波不稳定性。本项目基于回旋动理学理论及积分本征值程序HD7，系统地研究了中空电子密度分布下不稳定性的驱动机制、竞争条件及其对反常输运的贡献，讨论了背景等离子体和杂质离子对捕获电子模（TEM）与离子温度梯度（ITG）模线性增长率、激发阈值及准线性输运的影响，并将数值结果与实验观测做对比。.研究表明，TEM线性增长率随极向波数增加没有出现双峰结构，这和ITG模增长率随极向波数增加出现双峰结构的性质不同；ITG模/TEM在长（短）波长区间临界阈值较小（大）；在离（电）子加热占主导的等离子体中，TEM很容易（难）被激发，而ITG模则相反；在聚变反应堆的情况下（T_e/T_i~1），SWTEM的激发阈值小于SWITG模的激发阈值，因此SWTEM更容易被激发；尽管在远大于临界阈值的区间，SWITG模在峰化密度分布下更不稳定，但是中空电子密度分布下的临界阈值比峰化电子密度分布下的临界阈值小；捕获电子对SWITG模的致稳或者去稳效应依赖于捕获电子温度梯度和电子密度梯度等物理参数，这和长波长ITG模的结论不同。虽然SWITG模式可能比传统的长波长ITG模更不稳定，但是其引起的准线性湍动离子热传输的贡献很小，而要充分理解ITG模/TEM的非线性行为以及是否对真实托卡马克等离子体中的湍动输运有显著贡献，还有待进一步的研究。. 另一方面，杂质离子对ITG模/TEM的影响依赖于杂质的密度梯度、电离态、质量、温度梯度以及极向波数的共同效应；低电离态钨杂质对TEM产生的致稳效应几乎不随杂质密度梯度变化，而高电离态钨杂质对TEM的影响依赖于杂质密度梯度，并且不同的杂质离子对TEM激发阈值的影响并不明显。此外，发现轻杂质（碳、氧）离子的中空密度剖面比较陡峭时，杂质模被激发；相比峰化的电子密度剖面，轻（重）杂质模在中空电子密度剖面下较难（易）被激发；随电荷数增加，重杂质钨的（中空/峰化/平坦）密度剖面对杂质模激发阈值的影响逐渐减弱。