Effects of trapping electrons on synergy of lower-hybrid wave and electron cyclotron wave
Effects of trapping electrons on synergy of lower-hybrid wave and electron cyclotron wave
复制标题
俘获电子对低杂化波与电子回旋波协同作用的影响
DOI：
10.7498/aps.66.245202
复制
发表时间：
2017
影响因子：
1
通讯作者：
Xiang Nong
中科院分区：
文献类型：
--
作者：
Yang You-Lei;Hu Ye-Min;Xiang Nong
托卡马克聚变堆的稳态运行要求等离子体电流完全维持，并采用非感应方法进行控制。低杂波电流驱动是最有效的射频电流驱动方法，但其缺点是驱动电流分布难以控制。电子回旋电流驱动具有以高度局部化和鲁棒可控的方式来存款功率和驱动电流的能力，然而已知电子回旋电流驱动的效率显著低于低杂波电流驱动的效率。由于低杂波和电子回旋波的互补性，人们提出了将它们结合起来使用。在相同的等离子体条件下，通过同时使用波驱动的电流可能显著大于由波单独驱动的电流的总和，这就是所谓的协同效应。而低杂波电流驱动和电子回旋电流驱动都受到俘获效应的影响，这意味着低杂波电流驱动和电子回旋电流驱动之间的协同效应也可能与俘获效应密切相关。本文通过求解反弹平均准线性方程，研究了不同俘获角下俘获对低杂波与电子回旋电流驱动协同效应的影响。current.drive同时考虑了低杂波和电子回旋波引起的扩散。作为碰撞和波致扩散之间的平衡的所得到的稳态电子分布函数由CQL 3D代码数值获得，然后将其积分以计算驱动等离子体电流。为了理解协同过程的机理和物理过程，对速度-空间通量进行了分析。结果表明，随着俘获角的增大，波驱动的电流减小。随着俘获角的增大，协同因子也减小，这意味着在协同情况下的电流驱动过程比在单波情况下对俘获效应更敏感。电子回旋波驱动的电流随俘获角的增大而迅速下降，而低杂波的存在有助于减缓这种下降。较低的混合波降低了依赖性的电子回旋电流驱动上的陷阱。低杂波的共振区域越宽，解耦效应越强。提高电子回旋波功率，加速电子数增多，平行速度较高的电子数增多，协同效应增强，对俘获的依赖性降低。
Steady state operation is essential for Tokamak-based fusion reactor, in which the plasma current has to be fully.sustained and controlled by non-inductive methods. Lower-hybrid current drive is the most effective radio-frequency.current drive method, which, however, has the drawback that the driven current profile is difficult to control. Electron.cyclotron current drive has the ability to deposit power and drive current in a highly localized and robustly controllable.way, while the efficiency of electron cyclotron current drive is known to be significantly lower than that of lower-hybrid.current drive. Due to those complementary features, the combinative usage of lower-hybrid wave and electron cyclotron.wave has been proposed. The current driven by simultaneously using the waves might be significantly larger than the.sum of the currents driven by the waves individually in the same plasma conditions, which is the so-called synergy effect..While the lower-hybrid current drive and the electron cyclotron current drive are both affected by the trapping effect,.which implies that the synergy effect between lower-hybrid current drive and the electron cyclotron current drive may.also closely related to the trapping effect. In this paper, the effects of trapping on the synergy of lower-hybrid current.drive and the electron cyclotron current drive are investigated by solving the bounce-averaged quasi-linear equation.with different trapping angles. The diffusions induced by the lower-hybrid wave and the electron cyclotron wave are.considered simultaneously. The resulting steady-state electron distribution function as a balance between the collisions.and the wave-induced diffusions is obtained numerically by the CQL3D code, which is then integrated to calculate the.driven plasma current. The velocity-space fluxes are analyzed for understanding the mechanism and the physics of the.synergy process. It is found that the currents driven by the waves decrease as trapping angle increases. The synergy.factors also decrease as trapping angle increases, which means that the current drive processes in the synergy case.are more sensitive to the trapping effect than in the single wave case. The current driven by electron cyclotron wave.drops rapidly with the increase of trapping angle, while the existence of lower-hybrid wave is helpful in decelerating.the dropping. The lower-hybrid wave reduces the dependency of the electron cyclotron current drive on the trapping.effect. The decouple effect turns stronger as the resonance region of the lower-hybrid wave becomes wider. Increasing the.power of the electron cyclotron wave leads to more accelerated electrons and more electrons with relatively high parallel.velocities, which results in stronger synergy effect and less dependence on trapping.