Development And Experimental Study Of Spectroscopic Diagnostic System Of High Current Beam Source

Neutral Beam Injection(NBI)is a major auxiliary heating method for magnetic confinement fusion devices,the high current beam source is the key component of the whole neutral beam injector.Among them,the parameters of source plasma and the spatial distribution of beam intensity directly affect the heating effect and the safe,steady-state operation of neutral beam injector.Therefore,it has important value in engineering application to study the diagnostic technology and develop the diagnostic equipment for high current beam source.As a non-invasive measurement method,optical emission spectroscopy has the advantages of no disturbed,real-time,online and in-situ measurement.It can provide important information such as electron temperature,electron density,particle species of source plasma and spatial distribution of beam intensity,and it is the best diagnostic choice for the cognition of high current beam source.The main work of the paper is to use optical emission spectroscopy to conduct spectral measurement and experimental research on the high current beam source,which is summarized as follows:1.Based on the principle of plasma emission spectroscopy,the relationship between plasma parameters and radiation spectrum is expounded.The calculation models of particle density commonly used in low temperature plasma are analyzed.The criterion and calculation process of the partial local thermodynamic equilibrium model are described in detail.The compose particles,reaction processes and the effective rate coefficient of the argon collision radiation model and the hydrogen atom collision radiation model are analyzed.The electron temperature is calculated by the argon-helium atomic line ratio,and the electron density is calculated by the argon ion line-to-line ratio.Five excitation paths are analyzed theoretically,and the plasma parameters are measured using the hydrogen atomic Balmer line ratio.The generation mechanism of the beam emission spectrum is introduced,and the principle of beam emission spectrum diagnosis is expounded.2.Based on the principle of optical emission spectroscopy diagnostic,a set of source spectrum diagnostic system with measurement band of 400-900 nm and a set of beam emission spectroscopy diagnostic system are developed,which are mainly composed of pre-collecting component,optical fibers,grating spectrometer,detector,trigger,data acquisition and processing system.The key performance parameters of each component are introduced,the performance test and simulation analysis of the objective lens are carried out.The design and construction of the optical emission spectrum diagnostic system are completed.3.Based on the partial local thermodynamic equilibrium model,the electron temperature and ion density are calculated according to the universal Boltzmann distribution and the modified Shaha equation.The analysis results show that the partial local thermodynamic equilibrium model is not applicable to high current beam source,and the limitations of the model are analyzed.In view of the development and operation of the hot cathode arc source on the EAST device,the source spectrum diagnostic system is applied to the hot cathode ion source.Based on the comparison between the Langmuir probe measurement results and preliminary spectrum experimental results,this paper verifies the feasibility and the accuracy of spectral measurement of plasma parameters.The emission spectrum diagnostic method is further applied to NBI RF ion source,and electron temperature and electron density are measured.Due to the interference of the diagnostic gas on RF plasma discharge,a collision radiation model of hydrogen atom is developed,and preliminary experimental results are obtained.Therefore,the optical emission spectroscopy is used as a routine and on-line monitoring and diagnosis method for plasma parameter changes under different discharge conditions,which can analyze the discharge characteristics of high current beam source plasma.The beam emission spectroscopy diagnostic system is applied to the NBI device test platform,and the preliminary experimental results of the spatial distribution of beam intensity at the exit of the neutralization chamber of the NBI beam line are obtained.The analysis results show that the beam is deflected downward during the beam transmission process.