基于光弹调制的运动斯塔克效应诊断

电流密度分布是等离子体物理研究的关键分布参数,在托卡马克先进运行模式发展,电流驱动,约束与输运等方面发挥着重要的作用。中性束与等离子体相互作用产生的分裂光谱,包括σ分量与π分量,水平观测时,σ分量的偏振方向垂直于等效电场的方向,π分量的偏振方向平行于等效电场的方向,通过测量分裂光谱的偏振方向可以反演出等离子体电流密度分布。基于光弹调制器的偏振检测系统具有检测精度高、时间响应迅速的独特优点,非常适用于等离子体电流快速变化下的电流密度分布测量。光弹调制器的双折射晶体在周期性外部驱动源的作用下发生弹性形变,其折射率会产生周期性的变化,当偏振光通过时,出射光的偏振特性将相应产生周期性变化,再经过偏振片,形成调制的光强变化。运动斯塔克效应(MSE)诊断的偏振检测系统由两个光弹调制器(PEM)和一个偏振片组成,通过检测不同调制频率的调制强度的比值,从而快速、精确地获得分裂光谱的偏振方向的实时变化,进而得到等离子体电流密度分布。详细介绍了东方超环托卡马克(EAST)装置上的MSE诊断,初步完成了离线测试与标定,参与中性束电流本文驱动物理实验,初步获得了等离子体电流密度分布的信息。

A Photoelastic Modulator Based MSE Spectroscopic Diagnostic on EAST

Current density distribution is a crucial parameter in plasma physics, which plays an important role in plasma simulation, advanced operation mode development, current drive, confinement, and transport. The stark spectrum caused by injecting a neutral beam into plasma contains σ component, and π component. When viewed transversely to the electric field, the polarization direction of the σ component is perpendicular to the direction of the equivalent electric field, and the polarization direction of π component is parallel to the equivalent electric field, the distribution of current plasma density can be deduced by measuring polarization direction of the splitting spectrum.The polarization detection system based on a dual photoelastic modulator system has the unique advantages of high detection accuracy and quick time response, which is very suitable for measuring current density distribution under the rapid variation of plasma current. An external driving source causes the elastic deformation of birefringent crystals, and the refractive index changes periodically, then the modulated light intensity changes are formed through the polarizer. The polarization detection system of MSE diagnostic consists of two Photoelastic Modulators (PEM) and a polarizer. By detecting the ratio of modulation intensities at different modulation frequencies, the polarization direction of the splitting spectrum can be obtained quickly and accurately, and then the plasma current density distribution can be obtained. This paper introduces the polarization detection system of MSE diagnosis on Experimental Advanced Superconducting Tokamak (EAST), The off-line test and calibration of the system were completed, and the preliminary result of plasma current density distribution was obtained in experiments.