模拟快离子稳定微湍流的第一性原理
First principles of modelling the stabilization of microturbulence by fast ions
摘要：
快离子稳定离子温度梯度驱动的微湍流的观察对未来的聚变反应堆具有深远的意义。它在优化当今设备的性能方面也很重要。在这项工作中，我们详细研究了快速离子稳定的现象，并提出了一个简化的模型来描述这种效果。该模型是从高能量极限的gyrokinetic方程，并扩展了现有的“稀释”模型，占非平凡的快离子动力学。我们的模型提供了一个物理上透明的解释所观察到的稳定，并作出了几个关键的定性预测。第一，不同种类的快离子，取决于它们的径向密度或温度变化，具有不同的稳定特性。其次，正是因为快速离子带状响应可以忽略，所以带状流是这种效应的重要成分。最后，在高能量快离子的限制下，它们的响应接近“稀释”模型;特别是，α粒子预计对等离子体湍流几乎没有稳定作用。我们支持这些结论，通过详细的线性和非线性陀螺动力学模拟。
英文摘要：
The observation that fast ions stabilize ion-temperature-gradient-driven microturbulence has profound implications for future fusion reactors. It is also important in optimizing the performance of present-day devices. In this work, we examine in detail the phenomenology of fast ion stabilization and present a reduced model which describes this effect. This model is derived from the high-energy limit of the gyrokinetic equation and extends the existing "dilution" model to account for nontrivial fast ion kinetics. Our model provides a physically-transparent explanation for the observed stabilization and makes several key qualitative predictions. Firstly, that different classes of fast ions, depending on their radial density or temperature variation, have different stabilizing properties. Secondly, that zonal flows are an important ingredient in this effect precisely because the fast ion zonal response is negligible. Finally, that in the limit of highly-energetic fast ions, their response approaches that of the "dilution" model; in particular, alpha particles are expected to have little, if any, stabilizing effect on plasma turbulence. We support these conclusions through detailed linear and nonlinear gyrokinetic simulations.
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