EAST低杂波加热与电流驱动中谱间隙问题研究

The "spectral gap" is a well-known problem in the field of Lower Hybrid Wave(LHW) studies. LHW is a very important auxiliary heating and current drive method in the long pulse discharges on the EAST. However, considering that in the long pulse discharges on the EAST the electron temperature is not expected to be high, the "spectral gap" is very significant. The EAST is a relatively large aspect-ratio device comparing with other devices, it's difficult to solve that problem in the EAST through toroidal effect, and other effects might play important role and should be taken into account. As a result,in order to improve the current drive efficiency as well as the device operation efficiency, it's very necessary to systematically study and to solve the "spectral gap" problem in the Lower Hybrid Current Drive(LHCD) on the EAST. The ray-tracing and the full wave numerical modeling tools will be used, and the toroidal effect, the full wave effect and the scattering effect will be consequently taken into account in this research. On the one hand, based on the modeling, the effects of various regimes on bridging the "spectral gap" will be analyzed,the parameters which influence these effects respectively as well as their ranges should be found out,and via the comparison between the modeling and the coresponding experiments, the explanations to experiment observations and the optimized parameter ranges will be provided.On the other hand, the above works would be an important addition to the validation studies of these modeling tools and thus improvement should be made on these tools, which could be more helpful for the simulation of the LHW heating and current drive in the EAST. .

谱间隙是低杂波领域的一个很著名的问题。低杂波是EAST长脉冲放电过程中非常重要的辅助加热与电流驱动手段。而对于EAST中长脉冲放电实验来讲，电子温度相对较低,谱间隙问题尤其明显。由于EAST环径比比较大,环效应在填补谱间隙问题上存在困难，其他机制作用效应需要被考虑进来。系统地、充分地研究和解决EAST中低杂波的谱间隙问题对于提高其加热与电流驱动效率从而提高装置运行效率有着非常重要的意义。拟采用射线追踪、全波解等数值模拟手段,研究线性理论范畴的三个主要机制即环效应、全波效应和散射效应对于填补谱间隙的作用。一方面通过模拟研究，分析各种机制的作用以及找出影响各种机制作用的物理量及其参数范围，通过与EAST相关实验结合，提出解释实验现象的物理依据，预测优化的参数空间，另一方面也为这些模拟手段合理性验证提供重要补充以及改进，使之更好的为EAST装置低杂波加热和电流驱动模拟提供支撑。

研究EAST装置中低杂波加热与电流驱动存在谱间隙问题，有助于我们理解低杂波在EAST装置中传播和吸收的物理机制和实验现象。针对EAST中低杂波加热和电流驱动实验，通过数值模拟，我们主要分别考察了环效应、全波衍射效应以及由于密度扰动引起的低杂波散射效应对于低杂波传播和吸收的影响。通过和实验的对比以及相关参数扫描，我们得到了以下重要结论：只包含环效应，线性朗道阻尼给出的低杂波吸收可以是近轴也可以是离轴分布，但是由于准线性效应，低杂波的电流驱动是离轴分布；而包含全波衍射效应的全波解给出的低杂波吸收分布是离轴的，主要是通过充分的极向谱展宽使得低杂波在还没有传播到等离子体中心之前就已经被朗道阻尼；密度扰动引起的低杂波散射，可以使得低杂波垂直波数发生旋转，再通过环效应和磁剪切产生平行波数的变化，从而使得低杂波加热和电流驱动有相当的概率发生在近轴，并且通过模拟研究与密度扰动有关的参数，获得了和实验趋于一致的结果。我们在该领域研究方面取得了一些关键突破，包括：首次将模拟结果和EAST实验硬X射线数据进行了量化对比；通过相关的数值技巧，将全波模拟使用的极向模数由原来的2047首次提高到4095；通过相关数值平台的搭建以及优化，完成了全波和弗克-普朗克方程的完全自洽耦合模拟。此外本项目还做了该领域的相关研究，包括，通过解析和模拟研究了利用离轴低杂波电流驱动维持反磁剪切位形的相关参数；EAST上2.45GHz和4.6GH低杂波的耦合协同效应；为研究EAST低杂波在离子回旋频段波存在下的传播吸收性质，研究了快波模转换电流驱动；EAST中低杂波+中性束/离子回旋H模情况下的偏滤器靶板温度和热流研究等等。