Assessment of the limits of stability of tokamak plasmas is key to operation in high fusion performance ranges without disruption of the plasma current. Projected equilibria have been generated for the MAST-U spherical tokamak experiment, an upgrade of the previous MAST device, in order to prepare for operation. These equilibria are scanned in pressure and current profiles, and assessed with the DCON and MARS-F stability codes to find the so-called "no-wall" beta limit, above which resistive wall mode instabilities can be expected in the absence of other stabilising effects. The no-wall limit was generally found to increase as plasma internal inductance increased. The equilibria are also assessed for the "with-wall" limit, theoretically the highest achievable performance point, again with the DCON and MARS-F codes, including different approximate axisymmetric walls, and with the VALEN code which includes a 3D model of the surrounding conducting structure. Similar limits were found, despite the difference between the 2D and 3D codes in the treatment of the wall. Conducting passive stabilisation plates, which were newly installed in MAST-U, are in a region of significant mode perturbation when the plasma βN is sufficiently high and eddy currents are driven in these structures. Due to the increased stabilising effect of the wall in MAST-U vs. MAST, a significant gap exists between the approximate no-wall limits of βN/li = 6.71 and 7.13, found from DCON and MARS-F respectively, and the with-wall limits of βN/li = 8.23 and 8.53 for the equilibrium profiles analysed in this study. This opens a region of high beta operating space in MAST-U for potentially stable operation if non-ideal effects or active control can stabilise the resistive wall mode.

中文翻译：

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高β MAST-U 球形托卡马克等离子体的预计全局稳定性

托卡马克等离子体稳定性极限的评估是在高聚变性能范围内运行而不中断等离子体电流的关键。已为 MAST-U 球形托卡马克实验生成了预计的平衡，这是先前 MAST 设备的升级版，以便为操作做好准备。在压力和电流分布中扫描这些平衡，并使用 DCON 和 MARS-F 稳定性代码进行评估，以找到所谓的“无壁”β 极限，在没有其他稳定的情况下，可以预期电阻壁模式不稳定性高于该极限效果。通常发现无壁极限随着等离子体内部电感的增加而增加。平衡也被评估为“带壁”限制，理论上是最高可实现的性能点，再次使用 DCON 和 MARS-F 代码，包括不同的近似轴对称壁，以及包含周围导电结构 3D 模型的 VALEN 代码。尽管 2D 和 3D 代码在墙壁处理方面存在差异，但发现了类似的限制。当等离子体 βN 足够高并且在这些结构中驱动涡流时，新安装在 MAST-U 中的传导无源稳定板处于显着模式扰动的区域。由于 MAST-U 与 MAST 中壁的稳定作用增强，在分别从 DCON 和 MARS-F 中发现的近似无壁极限 βN/li = 6.71 和 7.13 之间存在显着差距，对于本研究中分析的平衡剖面，壁面限制 βN/li = 8.23 和 8.53。