Collisionality scaling of the electron heat flux in ETG turbulence
Collisionality scaling of the electron heat flux in ETG turbulence
复制标题
DOI：
10.1088/1361-6587/aa5f75
复制
发表时间：
2017-05-01
影响因子：
2.2
通讯作者：
Dorland, W.
中科院分区：
文献类型：
--
作者：
Colyer, G. J.;Schekochihin, A. A.;Dorland, W.
在电子-陀螺半径尺度上对MAST等离子体的静电模拟中，利用局部磁流管陀螺动力学代码GS2对绝热离子进行了模拟，发现随着电子碰撞的减小，长时间饱和电子热流（与能量输运最相关的水平）减小。在模拟初期，热通量“准饱和”，不依赖于碰撞，湍流以流状径向拉长结构为主。然而，纬向波动分量持续缓慢增长，直到较晚的时间，最终导致以纬向模态为主的新的饱和状态，热通量与碰撞率成正比，与实验观察到的MAST能量约束的碰撞尺度大致一致。我们基于一个由纬向-非纬向相互作用主导的ETG湍流模型和一个解析导出的带模阻尼率与电子-离子碰撞的标度，概述了对这种效应的解释。改进的能量约束与减少碰撞有利于未来的性能，更热的设备。
In electrostatic simulations of MAST plasma at electron-gyroradius scales, using the local fluxtube gyrokinetic code GS2 with adiabatic ions, we find that the long-time saturated electron heat flux (the level most relevant to energy transport) decreases as the electron collisionality decreases. At early simulation times, the heat flux 'quasi-saturates' without any strong dependence on collisionality, and with the turbulence dominated by streamer-like radially elongated structures. However, the zonal fluctuation component continues to grow slowly until much later times, eventually leading to a new saturated state dominated by zonal modes and with the heat flux proportional to the collision rate, in approximate agreement with the experimentally observed collisionality scaling of the energy confinement in MAST. We outline an explanation of this effect based on a model of ETG turbulence dominated by zonal-nonzonal interactions and on an analytically derived scaling of the zonal-mode damping rate with the electron-ion collisionality. Improved energy confinement with decreasing collisionality is favourable towards the performance of future, hotter devices.