Toroidal mode structure in weak and reversed magnetic shear plasmas and its role in the internal transport barrier
Toroidal mode structure in weak and reversed magnetic shear plasmas and its role in the internal transport barrier
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DOI：
10.1088/0741-3335/41/3a/060
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发表时间：
1999-03
影响因子：
2.2
通讯作者：
Y. Kishimoto;J. Kim;W. Horton;T. Tajima;M. Lebrun;H. Shirai
中科院分区：
文献类型：
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作者：
Y. Kishimoto;J. Kim;W. Horton;T. Tajima;M. Lebrun;H. Shirai
越来越清楚的是，在L模式托卡马克等离子体的异常输运占主导地位的径向扩展的非本地模式的环形几何形状。这表明，各种改进的模式，如在最近的反向磁剪切实验中形成的内部传输势垒（ITG），可以通过抑制这种全局结构的环形模式。我们调查的作用，等离子体剪切旋转和负/弱，并反向磁剪切对这些非本地模式采用我们的环形模拟代码与非本地理论。从模拟中，除了在整个负磁剪切区域的波激励的整体减少，我们发现，弱或零磁剪切出现在最小的q（安全系数）表面附近打破了环形耦合。这导致了一个不连续性（或差距）在波激发周围的表面，导致出现的运输障碍。实验中观察到的等离子体剪切旋转增强了不连续性，从而提高了不连续性的性能。我们还研究了这种ITG模式引起的自生径向电场的结构和相关的等离子体剪切旋转（称为纬向流），这些结构影响稳态中的波动水平。
It is becoming clear that anomalous transport in an L-mode tokamak plasma is dominated by radially extended non-local modes in toroidal geometry. This indicates that various improved modes such as the internal transport barrier (ITG) formed in a recent reversed magnetic shear experiment can be achieved by suppressing such a global structure of the toroidal mode. We investigate the role of plasma shear rotation and negative/weak and also reversed magnetic shear on these non-local modes by employing our toroidal simulation code together with a non-local theory. From simulations, in addition to the overall reduction of the wave excitation in the entire negative magnetic shear region, we find that the weak or zero magnetic shear which appears near the minimum q (safety factor) surface breaks up toroidal coupling. This leads to a discontinuity (or gap) in wave excitation around the -surface, leading to the emergence of the transport barrier. The plasma shear rotation which is observed in the experiment enhances the discontinuity so that the performance of the discontinuity is increased. We also investigate the structure of the self-generated radial electric field induced by such ITG modes and the related plasma shear rotation (referred to as the zonal flow) which influence the fluctuation level in the steady state.