先进托卡马克中通行高能离子驱动鱼骨模的数值模拟

Tokamak is the most hopeful magnetic confinement reactor, and it is highly desirable for the tokamak reactor to be a steady-state power station. ITER will also aim at steady state operation with the ratio of fusion power to auxiliary hearing power (Q) at least 5. With weak or negative magnetic shear (advanced scenarios)，plasmas can be mostly sustained by non-inductively driven current, and improve confinement and stability. Because there are significant differences between standard scenario and advanced scenario, the behaviors of MHD instability interactions with energetic particles are also distinct. The fishbone mode is global MHD instability driven by energetic particles, and it can induce significant losses of energetic particles. Understanding fishbone mode instability in advanced scenarios is essential for tokamak physics. In classical model, fishbone mode is driven by energetic trapped ions, but experimental results show that it can also be driven by energetic passing ions. Based on experimental results from HL-2A tokamak, this project plans to simulate the fishbone mode driven by energetic passing ions in advanced tokamak plasmas. The global gyro-kinetic/MHD hybrid code M3D-K will be used to analyze fishbone mode’s unstable region and nonlinear evolution. The aim of this project is to provide realistic numerical simulations, which could contribute for understanding experimental results and planning experiments in future.

托卡马克是目前最有希望的可控核聚变装置，实现稳态运行是其中的关键，也是ITER的首要目标。采用反磁剪切或者弱磁剪切的稳态运行模式（先进运行方案）是托卡马克最终用于发电的可行方案。先进运行模式由于电流剖面与标准运行模式有较大差异，所对应的磁流体不稳定性及其与高能粒子相互作用特性与标准方案存也存在很大区别。鱼骨模是高能粒子与磁流体相互作用引起的宏观不稳定性，会引起大量高能粒子损失。理解先进放电模式下鱼骨模不稳定性物理特征对于托卡马克的稳态运行方案研究有重要意义。本课题拟结合国内实验装置HL-2A，针对由中性束注入的通行离子激发鱼骨模不稳定性的现象，深入开展数值模拟研究。利用磁流体力学和回旋动理学混合模拟程序M3D-K分析在先进托卡马克运行方案下的鱼骨模不稳定性及其非线性演化。本课题主要研究目标是紧密结合实验，开展切合实际的数值模拟，为实验结果的分析、解释及将来的实验规划提供有实际意义的参考。

托卡马克是目前最有希望实现的可控核聚变实验装置，快粒子相关物理是实现稳态运行的关键。理解弱磁剪切和反磁剪切下磁流体不稳定性与高能粒子相互作用对于托卡马克的稳态运行方案研究有重要意义。本课题紧密结合托卡马克国际上NSTX和国内HL-2A托卡马克装置，深入开展弱磁剪切下快粒子驱动鱼骨模的数值模拟工作。利用磁流体力学和动理学混合模拟程序M3D-K分析在稳态运行方案下的鱼骨模不稳定性以及鱼骨模的非线性演化，并开发了鱼骨模线性稳定性分析程序dwk++。在NSTX中，通行快粒子在鱼骨鱼线性驱动的阶段比捕获粒子更加重要，贡献了驱动模式的再部分能量，而在非线性阶段，由于模式频率向下扫频，捕获粒子则贡献了非线性阶段的主要能量，最终带来通行粒子和捕获粒子的分布函数的重新分布。研究结果表明通行粒子驱动的鱼骨模可能分为高频和低频分支，分别对应通行粒子p=0 和p=-1两种不同的共振条件。对于高频鱼骨模，模式的共振条件比较容易满足，在目前托卡马克参数下粒子有限轨道宽度并不会对模式有显著影响，快粒子的空间分布对该模式有至关重要的影响。对于低频鱼骨模，p=0和p=-1的共振都不可忽略，同时快粒子的有限轨道宽度效应以及磁剪切都对模式的不稳定性有关键作用。