We present global linear and nonlinear simulations of ion temperature gradient instabilities based on a fluid formulation, with an adapted version of the JOREK code. These simulations are performed in realistic global tokamak equilibria based on the solution of the Grad–Shafranov equation. Benchmarking of linear growth rates was successfully completed with respect to previously published data. We find two distinct types of eigenstructures, depending on the magnetic shear. For high shear, when the coupling of poloidal harmonics is strong, ballooning-type eigenmodes are formed, which are up-down asymmetric with a finite ballooning angle, θ0. The poloidal harmonics which form the global eigenmode are found to demonstrate a radial shift, being centered well outside of their corresponding rational surface. Stronger diamagnetic effects increase both θ0 and proportionately shift the m harmonics to larger radii (by as much as two rational surfaces). In the low shear regime, the unstable eigenmodes become narrowly localized between neighboring pairs of rational surfaces, and exhibit no up-down asymmetry. Our simulations also show the generation of finite Reynolds stress due to nonlocal/global profile effects. This stress possesses both poloidally symmetric ( n = m = 0) and asymmetric (finite-m) components. Turbulent saturation in nonlinear simulations is demonstrated for both shear regimes.

中文翻译：

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全局 ITG 特征模态：从膨胀角和径向位移到雷诺应力和非线性饱和

我们展示了基于流体公式的离子温度梯度不稳定性的全局线性和非线性模拟，以及 JOREK 代码的改编版本。这些模拟是在基于 Grad-Shafranov 方程解的现实全球托卡马克平衡中进行的。相对于先前发布的数据，成功完成了线性增长率的基准测试。我们发现两种不同类型的本征结构，这取决于磁剪切。对于高剪切，当极向谐波的耦合很强时，形成膨胀型本征模式，其上下不对称，具有有限膨胀角 θ0。发现形成全局本征模的极向谐波表现出径向位移，其中心位于其相应的有理表面之外。更强的抗磁效应会增加 θ0 并按比例将 m 次谐波移动到更大的半径（多达两个有理面）。在低剪切状态下，不稳定的本征模式变得狭窄地定位在相邻的有理表面对之间，并且没有表现出上下不对称性。我们的模拟还显示了由于非局部/全局剖面效应而产生的有限雷诺应力。该应力同时具有极向对称 (n = m = 0) 和不对称 (有限 m) 分量。非线性模拟中的湍流饱和在两种剪切状态下都得到了证明。我们的模拟还显示了由于非局部/全局剖面效应而产生的有限雷诺应力。该应力同时具有极向对称 (n = m = 0) 和不对称 (有限 m) 分量。非线性模拟中的湍流饱和在两种剪切状态下都得到了证明。我们的模拟还显示了由于非局部/全局剖面效应而产生的有限雷诺应力。该应力同时具有极向对称 (n = m = 0) 和不对称 (有限 m) 分量。非线性模拟中的湍流饱和在两种剪切状态下都得到了证明。