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Performance near operational boundaries

机译：接近运营边界的性能

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The performance of ELMy II-mode operation in ASDEX Upgrade and JET is compared. Special attention is paid to variations (usually reductions) in this performance near the operational limits which will need to be approached in a next-step device. In JET it is found that input powers substantially above the H-mode threshold power are required to obtain discharges with energy confinement enhancement factors at or above the usual ELMy H-mode scalings. Such a margin (as much as a factor of two in JET) is not observed in ASDEX Upgrade. It is proposed that this difference may be due to the higher edge collisionality in ASDEX and the results are compared to a recent theory based on interchange instabilities and magnetic flutter. In ASDEX Upgrade, the confinement in type I ELMy discharges degrades as the density is raised due to a stiffness of the temperature profiles which leads to a degradation of the core confinement. This type of stiffness is observed in JET only at relatively high edge densities. In JET, the edge confinement degrades as the density is increased by external gas fuelling, consistent with a constant edge pressure gradient and an edge barrier width which reduces in proportion to the edge ion poloidal Larmor radius. In both machines, II-mode performance is limited at high density by a transition first to the type III ELM regime and then to the L-mode. The confinement penalty, relative to good type I ELM discharges, of operating with type III ELMs is about 25-30%. The maximum densities for operation with type I or type III ELMs can be substantially increased by increasing the plasma triangularity in both machines. [References: 26]
机译：比较了ASDEX升级和JET中ELMy II模式操作的性能。要特别注意在接近操作极限的情况下此性能的变化（通常会降低），这需要在下一步设备中解决。在JET中，发现需要获得实质上高于H模式阈值功率的输入功率，才能获得能量限制增强因子等于或高于常规ELMy H模式缩放比例的放电。在ASDEX升级中没有观察到这样的裕度（在JET中高达两倍）。有人提出，这种差异可能是由于ASDEX中较高的边缘碰撞性造成的，并且将结果与基于交换不稳定性和磁颤动的最新理论进行了比较。在ASDEX升级中，由于温度分布的刚度导致密度提高，因此，随着密度的增加，类型I ELMy放电的限制条件会降低，从而导致铁心限制条件的降低。仅在相对较高的边缘密度下才在JET中观察到这种类型的刚度。在JET中，边缘约束随着外部气体燃料的添加而随着密度的增加而降低，这与恒定的边缘压力梯度和边缘势垒宽度一致，边缘势垒宽度与边缘离子倍体拉莫尔半径成比例地减小。在这两种机器中，II模式的性能在高密度下都受到限制，首先要过渡到III型ELM机制，然后再过渡到L模式。相对于良好的I型ELM放电，使用III型ELM的禁闭罚款约为25％至30％。通过增加两台机器的等离子三角形性，可以大大提高I型或III型ELM的最大操作密度。 [参考：26]

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