Kinetic-ballooning-mode (KBM) turbulence is studied via gyrokinetic flux-tube simulations in three magnetic equilibria that exhibit small average magnetic shear: the Helically Symmetric eXperiment (HSX), the helical-axis Heliotron-J and a circular tokamak geometry. For HSX, the onset of KBM being the dominant instability at low wavenumber occurs at a critical value of normalized plasma pressure $\beta ^{\rm KBM}_{\rm crit}$ that is an order of magnitude smaller than the magnetohydrodynamic (MHD) ballooning limit $\beta ^{\rm MHD}_{\rm crit}$ when a strong ion temperature gradient (ITG) is present. However, $\beta ^{\rm KBM}_{\rm crit}$ increases and approaches the MHD ballooning limit as the ITG tends to zero. For these configurations, $\beta ^{\rm KBM}_{\rm crit}$ also increases as the magnitude of the average magnetic shear increases, regardless of the sign of the normalized magnetic shear. Simulations of Heliotron-J and a circular axisymmetric geometry display behaviour similar to HSX with respect to $\beta ^{\rm KBM}_{\rm crit}$ . Despite large KBM growth rates at long wavelengths in HSX, saturation of KBM turbulence with $\beta > \beta _{\rm crit}^{\rm KBM}$ is achievable in HSX and results in lower heat transport relative to the electrostatic limit by a factor of roughly five. Nonlinear simulations also show that KBM transport dominates the dynamics when KBMs are destabilized linearly, even if KBM growth rates are subdominant to ITG growth rates.

中文翻译：

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低平均磁剪切平衡中的动力学气球模式湍流

动力学气球模式 (KBM) 湍流是通过在三个磁平衡中的旋动通量管模拟来研究的，这些磁平衡表现出小的平均磁剪切：螺旋对称实验 (HSX)、螺旋轴 Heliotron-J 和圆形托卡马克几何。对于 HSX，KBM 的开始是低波数的主要不稳定性，发生在归一化等离子压力的临界值 $\beta ^{\rm KBM}_{\rm 暴击}$ 比磁流体动力学 (MHD) 膨胀极限小一个数量级 $\beta ^{\rm MHD}_{\rm 暴击}$ 当存在强离子温度梯度 (ITG) 时。然而， $\beta ^{\rm KBM}_{\rm 暴击}$ 随着 ITG 趋于零，增加并接近 MHD 膨胀极限。对于这些配置， $\beta ^{\rm KBM}_{\rm 暴击}$ 也随着平均磁切变幅度的增加而增加，而与归一化磁切变的符号无关。Heliotron-J 的模拟和圆形轴对称几何显示行为类似于 HSX $\beta ^{\rm KBM}_{\rm 暴击}$ . 尽管在 HSX 中长波长的 KBM 增长率很大，但 KBM 湍流的饱和度与 $\beta > \beta _{\rm 暴击}^{\rm KBM}$ 在 HSX 中是可以实现的，并导致相对于静电限制较低的热传输大约五倍。非线性模拟还表明，当 KBM 线性不稳定时，KBM 传输在动力学中占主导地位，即使 KBM 增长率低于 ITG 增长率。