Gyrokinetic Simulations of Short-Wavelength ITG Instability in the Presence of a Static Magnetic Island

The ion-temperature-gradient (ITG) mode instability in sheared slab geometry in the presence of a mesoscale magnetic island is investigated with a focus on the short-wavelength regime (kyρi > 1). We found that a static magnetic island causes radial and poloidal modes to couple and therefore plays a stabilizing role by allowing energy transfer from unstable modes to stable modes. However, for large island widths, the short-wavelength ITG mode becomes strongly destabilized and tends to dominate over the standard ITG mode (kyρi 0.5). A reduced model is proposed in this paper to understand this destabilization mechanism.

研究了存在中尺度磁岛时剪切平板几何结构中的离子温度梯度（ITG）模不稳定性，重点关注短波区域（$k_y\rho_i > 1$）。我们发现静态磁岛使径向模和极向模耦合，从而通过允许能量从不稳定模转移到稳定模起到稳定作用。然而，对于较大的磁岛宽度，短波ITG模变得强烈不稳定，并倾向于主导标准ITG模（$k_y\rho_i \approx 0.5$）。本文提出了一个简化模型来理解这种不稳定机制。