10月13日 Transport barrier formation induced by magnetic islands

报告题目：Transport barrier formation induced by magnetic islands

报告时间：2026年10月13日（星期二）14:30

报告地点：控制室三楼会议室

报 告 人：汪卫星

主 持 人：徐国盛

报告简介：

Gyrokinetic simulations that couple self-consistent neoclassical and turbulent effects show that internal transport barriers (ITBs) formed inside a rational magnetic surface in experiments can be induced by a magnetic island at the rational surface. The key effect is associated with changes in the E × B shear flow structure in the presence of the island. A magnetic island is shown to induce a neoclassical Er well across the island's inner boundary. However, a strong turbulence-driven Reynolds stress gradient across the island edge contributes to the continued growth of the E × B flow beyond the neoclassical level. The magnetic island is also shown to drive electric potential islands centered at both the inner and outer edges of the island. Depending on the island width, the island-induced $E \times B$ shear layer, along with the sheared vortex flows due to the low-n non-resonant potential islands, can effectively facilitate ITB formation via twofold effects: i) suppressing local turbulence in the inner core region next to the magnetic island and ii) preventing turbulence spreading from outside the shear layer to the inside. The latter effectively decouples the plasma inside the shear layer from the outside turbulent plasma. The simulation further suggests the existence of a critical island width to trigger an ITB, which underlies a connection of ITB formation to weak magnetic shears where magnetic islands tend to be wider for the same perturbation amplitude. Island rotation, as a major player, provides another key knob to control and optimize the ITB. Island rotation in the ion diamagnetic direction tends to deepen the Er well and shift the peaked E × B shear from the island's inner boundary to its outer boundary, therefore facilitating the formation of a broader, more stable ITB. The simulation results highlight the critical role of the interplay between neoclassical and turbulent physics in the ITB formation process.