The development of reliable H-modes on MAST, together with advances in heating power and a range of high spatial resolution diagnostics, has provided a platform to enable MAST to address some of the most important issues of tokamak stability. In particular the high β potential of the spherical tokamak is highlighted with stable operation at βN ∼ 5–6, βT ∼ 16% and βp up to ∼2. Magnetic diagnostic evaluation of the global β parameters is independently confirmed by kinetic profile data. Calculations indicate that the βN values are in the vicinity of no-wall stability limits. Studies of neoclassical tearing modes (NTMs) have been extended to explore their effects and develop avoidance strategies. Experiments have demonstrated that sawteeth play a strong role in triggering NTMs—by avoiding large sawteeth a much higher βN value has been reached. The significance of NTMs is confirmed, with large islands observed using the 300 point Thomson scattering diagnostic, and locking of large n = 1 modes frequently leading to disruptions, which become more rapid at low q95. The role of error fields has been explored. H-mode plasmas are also limited by edge localized modes (ELMs), with confinement degraded as the ELM frequency rises. However, in contrast to the conventional tokamak, the ELMs in high performing regimes on MAST (HIPB98Y2 ∼ 1) appear to be type III in nature. Modelling using the ELITE code, which incorporates finite n corrections, identifies instability to peeling modes, consistent with a type III interpretation. It also shows considerable scope to raise pressure gradients before ballooning type modes (perhaps associated with type I ELMs) occur. The calculations show that narrow pedestals can support much stronger pressure gradients than might be expected from simple n = ∞ ballooning calculations. Finally sawteeth are shown to degrade confinement by ∼10–15% in particular cases examined. They are observed not to remove the q = 1 surface in the cases where snakes are present—various physics models of the sawteeth are now being explored. Thus research on MAST is not only demonstrating stable operation at high performance levels and developing methods to control instabilities; it is also providing detailed tests of the stability physics and models applicable to conventional tokamaks, such as ITER.
MAST装置上可靠H模的发展，连同加热功率的提升和一系列高空间分辨率诊断手段的进步，为MAST装置研究托卡马克稳定性中一些最重要的问题提供了平台。特别是，球形托卡马克的高β潜力通过在βN ∼ 5–6、βT ∼ 16% 以及βp高达 ∼2 条件下的稳定运行得到了凸显。全局β参数的磁诊断评估结果与动力学剖面数据独立地相互印证。计算表明，βN值接近无壁稳定性极限。对新经典撕裂模（NTMs）的研究已扩展到探索其影响并制定避免策略。实验证明，锯齿振荡在触发NTM方面起着重要作用——通过避免大锯齿，可获得显著更高的βN值。NTM的重要性已得到证实，通过300点汤姆逊散射诊断观测到了大尺度磁岛，并且大n=1模的锁定频繁导致破裂，而在低q95条件下破裂过程更为迅速。误差场的作用也已得到探索。H模等离子体还受到边缘局域模（ELMs）的限制，随着ELM频率的增加，约束性能下降。然而，与常规托卡马克不同，在MAST装置高性能运行状态下（HIPB98Y2 ∼ 1），ELM似乎表现为III型。使用ELITE代码进行的模拟（该代码包含了有限n修正）识别出不稳定性为剥离模，这与III型ELM的解释一致。计算还表明，在剥离模触发之前，存在相当大的空间来提高边缘压力梯度，而气球模（可能与I型ELM相关）则限制了这一空间。计算结果显示，窄台基能够支撑比简单n = ∞气球模计算所预测的强得多的压力梯度。最后，研究表明锯齿振荡在特定情况下会使约束性能降低约10–15%。在存在蛇形振荡的情况下，观测到锯齿振荡并未消除q = 1面。目前正在探索各种关于锯齿振荡的物理模型。因此，在MAST装置上的研究不仅展示了在高性能水平下的稳定运行，并发展了不稳定性控制方法，而且为适用于常规托卡马克（如ITER）的稳定性物理和模型提供了详细的检验。