Comparative studies of core and edge transport barrier dynamics of DIII-D and TFTR tokamak plasmas
Comparative studies of core and edge transport barrier dynamics of DIII-D and TFTR tokamak plasmas
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DOI：
10.1088/0029-5515/39/11y/313
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发表时间：
1999-11-01
期刊：
影响因子：
3.3
通讯作者：
Zarnstorff, MC
中科院分区：
文献类型：
--
作者：
Synakowski, EJ;Beer, MA;Zarnstorff, MC
为了确定共同的物理基础，比较了TFTR核和DIII-D核和边缘中增强约束制度的等离子体动力学。尽管在过渡时间尺度和位置以及径向电场E-r的符号上存在差异，但观测结果表明，在所有情况下，E x B剪切对湍流诱导输运的影响在控制障壁动力学方面都起着主导作用。在TFTR核心增强反剪切（ERS）模式和边缘DIII-D H模式下观察到快速约束分岔。在约束变化之前，两者都表现出自发的E-r剪切层的形成，并且随着陡峭梯度的形成，负E-r井持续存在。这些动力学不同于DIII-D阴性中心剪切（NCS）等离子体。当单向光束注入的扭矩较小时，可以观察到缓慢的转变，而当施加的扭矩较大时，则会出现更快的发展和更显著的约束改善。与H模态和ERS模态不同，NCS核通常有一个正的E-r hill，没有强的E-r剪切前体。然而，在TFTR上进行的相似实验表明，在恒定功率下，通过改变施加的扭矩来改变E × B剪切，可以以连续的方式获得ERS、L模式和NCS-like模式。在DIII-D NCS中，TFTR反向剪切等离子体的核心约束随着共旋转开始主导E-r的测定而缓慢改善，在此改善之前没有形成强E-r剪切层，并且等离子体具有正E-r hill。输运随E-r梯度的减小与E x B剪切抑制和湍流解相关的图像一致。在固定的输入功率，中间水平的约束改善是通过改变E x B剪切与应用中性梁扭矩的变化来实现的。数据表明，如果使用外部的E x B剪切源（例如可能应用于射频技术）来修改否则发生的剪切，则可以控制反应器中的等离子体压力分布。
The plasma dynamics of enhanced confinement regimes in the TFTR core and the DIII-D core and edge are compared in order to identify a common physics basis. Despite differences in transition timescale and location, as well as the sign of the radial electric field E-r, observations suggest that E x B shear effects on turbulence induced transport play a dominant role in governing barrier dynamics in all cases. Fast confinement bifurcations are observed in the TFTR core enhanced reverse shear (ERS) regime and in the edge DIII-D H mode. Both show spontaneous E-r shear layer formation prior to the confinement change and a negative E-r well that persists as steep gradients form. These dynamics differ from those of DIII-D negative central shear (NCS) plasmas. There, slow transitions are observed when the applied torque from unidirectional beam injection is small, while faster development and more dramatic confinement improvements occur at higher applied torques. Unlike the H mode and ERS cases, the NCS core generally has a positive E-r hill and no strong E-r shear precursor. However, similarity experiments performed on TFTR indicate that ERS, L mode and NCS-like regimes can all be accessed in a continuous fashion by varying the E x B shear through changes in the applied torque at constant power. As in the DIII-D NCS case, core confinement in TFTR reverse shear plasmas improves slowly as co-rotation begins to dominate the determination of E-r, no strong E-r shear layer develops prior to that improvement, and the plasma possesses a positive E-r hill. Reductions in transport with E-r gradients of either sign are consistent with the picture of E x B shear suppression and decorrelation of turbulence. At fixed input power, intermediate levels of confinement improvement are achieved by varying the E x B shear with changes in the applied neutral beam torque. The data suggest that control over the plasma pressure profile in a reactor may be possible if an external source of E x B shear, such as might be applied with RF techniques, is used to modify the shear which otherwise occurs.