The tokamak approach, utilizing a toroidal magnetic field configuration to confine a hot plasma, is one of the most promising designs for developing reactors that can exploit nuclear fusion to generate electrical energy^1,2. To reach the goal of an economical reactor, most tokamak reactor designs^{3,4,5,6,7,8,9,10} simultaneously require reaching a plasma line-averaged density above an empirical limit—the so-called Greenwald density¹¹—and attaining an energy confinement quality better than the standard high-confinement mode^12,13. However, such an operating regime has never been verified in experiments. In addition, a long-standing challenge in the high-confinement mode has been the compatibility between a high-performance core and avoiding large, transient edge perturbations that can cause very high heat loads on the plasma-facing-components in tokamaks. Here we report the demonstration of stable tokamak plasmas with a line-averaged density approximately 20% above the Greenwald density and an energy confinement quality of approximately 50% better than the standard high-confinement mode, which was realized by taking advantage of the enhanced suppression of turbulent transport granted by high density-gradients in the high-poloidal-beta scenario^14,15. Furthermore, our experimental results show an integration of very low edge transient perturbations with the high normalized density and confinement core. The operating regime we report supports some critical requirements in many fusion reactor designs all over the world and opens a potential avenue to an operating point for producing economically attractive fusion energy.

托卡马克方法利用环形磁场配置来限制热等离子体，是开发利用核聚变产生电能的反应堆最有前途的设计之一^1,2。为了实现经济反应堆的目标，大多数托卡马克反应堆设计^{3,4,5,6,7,8,9,10}同时要求达到高于经验极限的等离子体线平均密度 - 所谓的格林沃尔德密度¹¹ -并获得比标准高约束模式更好的能量约束质量^12,13。然而，这种操作方式从未在实验中得到验证。此外，高约束模式中长期存在的挑战是高性能核心与避免大的瞬态边缘扰动之间的兼容性，这种扰动可能会导致托卡马克中面向等离子体的组件产生非常高的热负载。在这里，我们报告了稳定托卡马克等离子体的演示，其线平均密度比格林沃尔德密度高约20％，能量限制质量比标准高限制模式好约50％，这是通过利用增强抑制实现的高极向β情景中高密度梯度所赋予的湍流传输^14,15。此外，我们的实验结果表明非常低的边缘瞬态扰动与高归一化密度和限制核心的集成。我们报告的运行机制支持世界各地许多聚变反应堆设计中的一些关键要求，并为生产具有经济吸引力的聚变能开辟了一条通往运行点的潜在途径。