In tokamaks, a leading platform for fusion energy, periodic filamentary plasma eruptions known as edge-localized modes occur in plasmas with high-energy confinement and steep pressure profiles at the plasma edge. These edge-localized modes could damage the tokamak wall but can be suppressed using small three-dimensional magnetic perturbations. Here we demonstrate that these magnetic perturbations can change the magnetic topology just inside the steep gradient region of the plasma edge. We identify signatures of a magnetic island, and their observation is linked to the suppression of edge-localized modes. We compare high-resolution measurements of perturbed magnetic surfaces with predictions from ideal magnetohydrodynamic theory where the magnetic topology is preserved. Although ideal magnetohydrodynamics adequately describes the measurements in plasmas exhibiting edge-localized modes, it proves insufficient for plasmas where these modes are suppressed. Nonlinear resistive magnetohydrodynamic modelling supports this observation. Our study experimentally confirms the predicted role of magnetic islands in inhibiting the occurrence of edge-localized modes. This will be beneficial for physics-based predictions in future fusion devices to control these modes.

在聚变能的领先平台托卡马克中，周期性的丝状等离子体喷发（称为边缘定位模式）发生在等离子体边缘具有高能量约束和陡峭压力剖面的等离子体中。这些边缘定位模式可能会损坏托卡马克壁，但可以使用小的三维磁扰动来抑制。在这里，我们证明了这些磁扰动可以改变等离子体边缘陡峭梯度区域内的磁性拓扑。我们识别了磁岛的特征，它们的观察与边缘定位模式的抑制有关。我们将扰动磁表面的高分辨率测量与理想磁流体动力学理论的预测进行了比较，其中保留了磁性拓扑结构。尽管理想的磁流体动力学充分描述了表现出边缘定位模式的等离子体中的测量值，但事实证明，对于这些模式被抑制的等离子体来说，它是不够的。非线性电阻磁流体动力学模型支持这一观察结果。我们的研究通过实验证实了磁岛在抑制边缘定位模式发生中的预测作用。这将有利于未来聚变装置中基于物理的预测来控制这些模式。