Ida K, Yoshinuma M, Tsuchiya H, Kobayashi T, Suzuki C, Yokoyama M, Shimizu A, Nagaoka K, Inagaki S, Itoh K
National Institute for Fusion Science, Toki, Gifu 509-5292, Japan.
Research Institute for Applied Mechanics, Kyushu University, Kasuga 816-8580, Japan.
Nat Commun. 2015 Jan 8;6:5816. doi: 10.1038/ncomms6816.
The driving and damping mechanism of plasma flow is an important issue because flow shear has a significant impact on turbulence in a plasma, which determines the transport in the magnetized plasma. Here we report clear evidence of the flow damping due to stochastization of the magnetic field. Abrupt damping of the toroidal flow associated with a transition from a nested magnetic flux surface to a stochastic magnetic field is observed when the magnetic shear at the rational surface decreases to 0.5 in the large helical device. This flow damping and resulting profile flattening are much stronger than expected from the Rechester-Rosenbluth model. The toroidal flow shear shows a linear decay, while the ion temperature gradient shows an exponential decay. This observation suggests that the flow damping is due to the change in the non-diffusive term of momentum transport.
等离子体流的驱动和阻尼机制是一个重要问题，因为流剪切对等离子体中的湍流有显著影响，而湍流决定了磁化等离子体中的输运。在此，我们报告了由于磁场随机化导致流阻尼的明确证据。在大型螺旋装置中，当有理面上的磁剪切降至0.5时，观察到与从嵌套磁通量面到随机磁场的转变相关的环向流突然阻尼。这种流阻尼以及由此导致的分布变平比瑞切斯特 - 罗森布鲁斯模型预期的要强得多。环向流剪切呈线性衰减，而离子温度梯度呈指数衰减。这一观察结果表明，流阻尼是由于动量输运的非扩散项的变化所致。
