AI 中文总结
研究STEP中电磁湍流局部陀螺动力学模拟里向大热量通量的非线性转变，借助应力平衡框架，通过大量模拟表明转变由静电和磁颤应力平衡控制，给出相关临界值及不同托卡马克情况，为识别禁区预测提供框架，增进对电磁饱和物理的理解。
AI 中文摘要
本工作研究了在STEP中电磁湍流的局部陀螺动力学模拟中观察到的向大热通量的非线性转变。利用Zhang等人的应力平衡框架，确认极端输运的开始与$q^{2}\beta_{e}$的临界值相关，其中$q$是安全因子，$\beta_{e}$是电子热压力与磁压力之比，并将其与极向β$\beta_{\mathrm{pol}}$的极限联系起来。关键的是，该临界值低于（$q$，$\beta_{e}$）空间中任何相关的线性稳定极限。通过大量非线性陀螺动力学模拟表明，STEP中向大通量的转变由静电和磁颤应力之间的平衡控制。还表明较大主半径托卡马克在较低$\beta_{e}$时达到电磁非带状区域，使这种磁流体动力学控制的饱和极限在反应堆规模装置中比在小型球形托卡马克中更容易达到。进入第二稳定状态能在更大$\beta^{\prime}$值时重新饱和。理想气球模阈值可用于划定第二稳定区域并作为大热通量开始的定性指南。这些结果为从局部陀螺动力学识别禁区预测提供了一个预测框架，并为与STEP和其他高$\beta_{e}$装置相关的电磁饱和物理提供了新见解。
英文摘要
This work investigates the nonlinear transition to large heat fluxes observed in local gyrokinetic simulations of electromagnetic turbulence in STEP. Using the stress-balance framework of Zhang et al. (arXiv:2606.04616, arXiv:2607.11789), we confirm that the onset of extreme transport correlates with a critical value of $q^{2}β_{e}$, where $q$ is the safety factor and $β_{e}$ is the ratio of electron thermal pressure to magnetic pressure, and relate this to a limit on the poloidal beta $β_{\mathrm{pol}}$. Crucially, this critical value lies below any relevant linear stability limit in the ($q$, $β_{e}$) space (e.g., the onset of ideal or kinetic ballooning modes). Using an extensive set of nonlinear gyrokinetic simulations, we demonstrate that the transition to large fluxes in STEP is governed by a balance between the electrostatic and magnetic-flutter stresses. We argue, and also show numerically, that larger-major-radius tokamaks reach the electromagnetic non-zonal regime at lower $β_{e}$, making this MHD-controlled saturation limit more accessible in reactor-scale devices than in small spherical tokamaks. We also demonstrate that access to a second-stable regime enables re-saturation at larger values of $β^{\prime}$. We further show that the ideal ballooning mode (IBM) threshold serves as a useful proxy for delineating this second-stable region and also as a qualitative guide for the onset of large fluxes. These results provide a predictive framework for identifying no-go zone predictions from local gyrokinetics and offer new insight into the electromagnetic saturation physics relevant to STEP and other high-$β_{e}$ devices.
