Roles of non-axisymmetric perturbations in free drift vertical displacement events on EAST

Haolong Li, Ping Zhu, Hang Li, Muquan Wu, Xiang Zhu, Jingting Luo2024年8月Nuclear FusionIF 3 出版社

The safe operation of most tokamaks, especially the large ones, relies on the feedback control of vertical displacement events (VDEs). However, most of these feedback control systems are based on axisymmetric VDE models. In this study, we use NIMROD simulations to study the role of non-axisymmetric perturbations in free drift vertical displacement events on EAST. The high-n modes in the non-axisymmetric VDE grow first, which drives the formation of high-n magnetic island chains. Subsequently, the magnetic island chains grow and overlap with each other, leading to the destruction of the magnetic flux surface, which induces a minor disruption and accelerates the start of the following major disruption. The magnetic island and the stochastic magnetic field allow the toroidally non-axisymmetric poloidal plasma current to jet towards the hoop force direction, forming finger-like and filamentary structures. Such a plasma current non-axisymmetry strongly depends on the anisotropy in the thermal transport coefficients.

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ENThis paper is of interest to fusion researchers, particularly those working on tokamak stability and feedback control systems, as it provides insights into the complex dynamics of VDEs and the importance of considering non-axisymmetric effects.#tokamak #VDE #EAST #NIMROD #magneticislands #disruption

This paper investigates the role of non-axisymmetric perturbations in vertical displacement events (VDEs) on the EAST tokamak. The study uses NIMROD simulations to show that high-n modes in non-axisymmetric VDEs can lead to the formation of magnetic island chains, which can disrupt the magnetic flux surfaces and accelerate major disruptions. The resulting non-axisymmetric plasma current can form finger-like and filamentary structures, strongly depending on the anisotropy in thermal transport coefficients.

この研究では、NIMROD シミュレーションを使って、EASTにおける自由ドリフト垂直変位事象における非軸対称擾乱の役割を調べた。高n モードが最初に成長し、高n 磁気島鎖の形成を引き起こす。その後、磁気島鎖が成長して重なり合い、磁束面を破壊し、小規模な disruption を引き起こす。これにより、トロイダル方向の非軸対称な電流が発生し、指状や糸状の構造を形成する。