汤姆逊散射技术在HL-2A装置上的应用进展

非相干激光汤姆逊散射诊断只需要假设电子速度满足Maxwell分布,测量得到的等离子体电子温度与电子密度的数据准确可靠,是托卡马克和其他磁约束核聚变研究装置上重要的诊断工具,并朝着高可靠性、高空间分辨和高重复测量频率的方向发展,其中高可靠性是前提。电子的汤姆逊散射截面很小,其总截面为σ_T=6.65×10^-25 cm²,通常使用电光调Q的Nd∶YAG激光器作为散射光源,激光脉冲宽度约10 ns、脉冲能量约3 J,用5～8通道的光谱仪对散射光谱进行测量与分析。如何对光电探测模块输出的散射脉冲进行数据采集,是激光散射诊断的关键问题之一。以前使用电流积分式的数据采集器(Q-ADCs,如CMC080模块),在一个确定的时间宽度(如50 ns)将散射脉冲信号积分在采样电容器上,从而得到散射信号的强度值,这种方法很难排除电路噪声和外来干扰。该研究通过使用高速数据采集器(纵向分辨率≥10 bits、采样频率f≥1 GS·s^-1,如V1742B模块)在包含散射信号在内的时间段(如300～500 ns)进行采集,获得散射...

Progress of Thomson Scattering Diagnostic on HL-2A Tokamak

The diagnosis of incoherent laser Thomson scattering only needs to assume that the electron velocity satisfies the Maxwell distribution,and the measured data of plasma electron temperature and electron density are accurate and reliable.It is an important diagnostic tool in the Tokamak and other magnetically confined fusion research device,and it is developing towards the measurement requirements of high reliability,high spatial resolution and high repetition rate,while high reliability is the premise condition.The Thomson scattering cross section of electron is very small,and its total cross section isσT=6.65×10-25 cm 2.Generally,the Q-switched Nd∶YAG laser is used as the scattering light source.The laser pulse width is about 10 ns,and the pulse energy is about 3 J.The scattering spectrum is measured and analyzed by a 5~8 channel polychromator.One of the key problems of laser scattering diagnosis is how to collect the scattering-related electric pulse output from photoelectric detection module.In the past,charge-sensitive analogue-to-digital converters(Q-ADCs,such as CMC080 module)were used to integrate the scattered pulse signal on the sampling capacitor over a certain time width(such as 50 ns),so as to obtain the strength value of the scattered signal.This method is difficult to eliminate circuit noise and external interference.Now,fast digitizers(vertical resolution≥10 bits,sampling frequency f≥1 GS·s^-1,such as V1742B module)are used to collect the data in the time period including the scattering signal(such as 300~500 ns),so as to obtain the data sequence superimposed by the scattering pulse signal,the disturbance of plasma light and background noise.In this paper,the least square method is used to fit the scattering pulse with Gaussian function,and then the scattering pulse is numerically integrated into 50 ns-width to get the strength value of the scattering signal.The results show that the use of high-speed synchronous acquisition technology can eliminate most of the interference with digital filtering technology,so as to improve the signal-to-noise ratio,and its amplitude can reach about 10 times.After more accurate and reliable spectral data are extracted,the error-weighted least square method is used to process the data at the confidence level of 95%.A.C.Selden scattering spectral expression is used to estimate the parameters of electron temperature,and the measured value of electron temperature is obtained.The statistical error is about 3%,which is better than the previous 10%.