基于J-TEXT远红外偏振干涉仪的相干散射与密度扰动的实验研究

Research on plasma transport is essential for magnetic confinement fusion research. The measurement of microscopic density fluctuations in plasma is important for the research of plasma transport. The recent J-TEXT density limit experiment showed that the density limit disruption was related to the plasma transport. And a diagnostic system for the measurement of microscopic density fluctuations should be developed to enhance the investigation of the inner mechanism of density limit disruption. A heterodyne coherent scattering measurement system based on the far-infrared polarimeter-interferometer is planned to develope to measure the microscopic density fluctuations in J-TEXT plasma. The main research contents of this project are the realization of heterodyne far-infrared coherent scattering system, the analysis of far forward scattering signal and the features of density fluctuation spectrum. The study will be focused on the high density plasma and the density limit disruption plasma. Moreover, the role of the high density ion mode-ITG played in the transition of LOC to SOC as well as the density limit disruption will be studied. The effects of ITG on the plasma profile will also be studied .The particle transport character will be investigated by means of the perturbative transport analysis method of density modulation.

等离子体输运是磁约束聚变的主要研究方向，等离子体微观密度涨落研究是输运实验研究的重要内容。申请人近期在J-TEXT上开展的密度极限实验显示，密度极限破裂与等离子体输运之间存在关联。为深入研究密度极限破裂的内在机制，必须发展能够测量微观密度扰动的诊断手段。本项目拟利用J-TEXT上的三色远红外激光偏振干涉仪构建外差式相干散射测量系统，在保证偏振干涉仪运行的同时利用激光的前向散射信号获取微观密度扰动信息。本项目的主要研究内容是前向散射信号的识别与提取，各种实验条件下的密度扰动谱的特征研究。重点研究高密度和密度极限下的密度扰动特征，等离子体约束从LOC向SOC转变时，高密度离子模式—离子温度梯度模ITG的作用，以及ITG在密度极限破裂中的作用和其对等离子体剖面的影响。结合密度调制的扰动输运研究方法，研究密度极限下的粒子输运特性。

本项目利用J-TEXT上的三色远红外激光偏振干涉仪构建了多道外差式相干散射测量系统，在保证偏振干涉仪运行的同时利用激光的前向散射信号获取微观密度扰动信息。利用改进的数据处理方法，识别了低频密度涨落信息，利用探测光的折射效应，发展了等离子体密度涨落传播方向的判断方法。基于前向相干散射测量，在J-TEXT等离子体中观察到了准相干模式的密度涨落，其传播方向为离子逆磁方向。通过密度爬升实验，研究了各种实验条件下的密度扰动谱和等离子体输运特性，确定了在等离子体的高密度和边界区域，等离子体输运主要由低频的准相干模式主导。本项目的开展，使得三色偏振仪系统成为J-TEXT托卡马克装置上可以同时获取等离子体边界和芯部密度扰动信息的有效诊断，进一步夯实了该装置的物理研究基础。