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arXiv 2311.04028physics.plasm-phnlin.CD
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辛映射中的混沌输运:在等离子体中的应用

Chaotic transport in symplectic maps: Applications in plasma

Matheus Silva Palmero

AI总结:

本研究针对托卡马克磁力线建模的两种辛映射,提出数值方法分析其混合相空间混沌输运特性,揭示不变流形输运通道与黏滞现象,可为托卡马克放电参数优化提供支撑。

摘要:

混沌输运与哈密顿系统中混沌轨迹的复杂动力学演化相关,可对多种物理过程进行建模。在磁约束等离子体中,可通过合适辛映射的相空间对磁场构型进行定性描述。这类相空间为混合型,混沌与规则运动共存,全面理解混沌输运是一项挑战,攻克该挑战可进一步深化对约束聚变等离子体行为的认知。本研究聚焦于两种辛映射的混合相空间中的混沌输运特性,这两种映射用于模拟不同构型下托卡马克的磁力线。单零偏滤器映射(Boozer映射)用于模拟带有极向偏滤器的托卡马克的磁力线;遍历磁限制器映射(Ullmann映射)用于模拟装配有遍历磁限制器的托卡马克的磁构型。我们提出了两种数值方法,用于研究并阐明两种模型中开放磁力线瞬态行为的差异,同时考虑了增强或抑制逃逸磁力线的诱导磁构型。第一项分析表明,不变流形的空间结构为开放磁力线构建了适配的输运通道,对所选磁构型中的平均动力学演化产生影响。第二项分析识别出与平均混沌行为差异显著的轨迹,具体检测到了黏滞现象,该现象可能与等离子体边缘磁岛最近邻区域内的额外约束区相关。这些分析最终可助力选择最优实验参数,以实现托卡马克放电的特定目标。

英文摘要:

Chaotic transport is related to the complex dynamical evolution of chaotic trajectories in Hamiltonian systems, which models various physical processes. In magnetically confined plasma, it is possible to qualitatively describe the configuration of the magnetic field via the phase space of suitable symplectic maps. These phase spaces are of mixed type, where chaos coexists with regular motion, and the complete understanding of the chaotic transport is a challenge that, when overcomed, may provide further knowledge into the behaviour of confined fusion plasma. In this research, we focus our investigation on properties of chaotic transport in mixed phase spaces of two symplectic maps that model the magnetic field lines of tokamaks under distinct configurations. The single-null divertor map, or Boozer map, models the field lines of tokamaks with poloidal divertors. The ergodic magnetic limiter map, or Ullmann map, models the magnetic configuration of tokamaks assembled with ergodic magnetic limiters. We propose two numerical methods developed to study and illustrate the differences between the transient behaviour of open field lines in both models while considering induced magnetic configurations that either enhance or restrain the escaping field lines. The first analysis shows that the spatial organisation of invariant manifolds creates fitting transport channels for the open field lines, influencing the average dynamical evolution in the selected magnetic configurations. The second identifies trajectories that widely differs from the average chaotic behaviour, specifically detecting the stickiness phenomenon, which can be related to additional confinement regions in the nearest surroundings of magnetic islands in the plasma edge. These analyses may, ultimately, assist in selecting optimal experimental parameters to achieve specific goals in tokamak discharges.

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