Investigation On Collisional Radiative Model And Optical Emission Spectroscopy For Hydrogen Plasmas In Radio Frequency Driven Negative Ion Source

Radio frequency?RF?driven negative ion source is the core component of neutral beam injector for large magnetic confinement nuclear fusion device.How to generate and extract high density negative ions is the hotspot and difficulty in research.Plasma parameters should be obtained to optimize the formation of negative ions,which involves a series of quite complex physical and chemical processes.Optical emission spectroscopy?OES?with non-invasive characteristics is a necessary diagnostic method for large ion sources.Collisional radiative models?CR models?or coronal models,which build the relationship between spectroscopy and plasma parameters are needed for OES.The main goal of this work is to establish a CR model of atomic hydrogen and a coronal model of molecular hydrogen and to develop a set of software about model calculation and OES for the ion source in Huazhong University of Science and Technology?HUST?.In this thesis,a CR model including multiple excitation channels for atomic hydrogen is established.Moreover,the excitation channels in different positions of the source are analyzed based on the typical plasma parameters.The direct excitation of H,dissociative excitation of H₂ and dissociative recombination of H₂⁺in the driver dominate and direct excitation of H accounts for more than 70%.However,near the plasma grid,the direct excitation of H and the dissociative recombination of H₂⁺take the major share.For H?3?,the neutralization of H^-cannot be ignored.The effect of electron energy distribution function?EEDF?on the results of the CR model is studied.Population densities of exited states under Maxwellian distribution are higher at low electron temperature,but as the electron temperature is high,population densities of exited states under Druyvesteyn distribution are higher.The above effect is especially significant at low electron temperature.When electron temperature or electron densities increase and the EEDF deviates from Maxwellian to become more Druyvesteyn like,the excited atomic hydrogen densities can stay constant or even decrease.In addition,a rovibrationally resolved coronal model of molecular hydrogen is built.The contribution of different vibrational/rotational levels in hydrogen molecule ground state to vibrational/rotational levels in excited state is investigated.We point out that when electron temperature and vibrational temperature vary,the evolution of the contribution of vibrational levels in ground state can be divided into three regions:the ground vibrational level leading region;the vibrational temperature and Franck-Condon factors jointly affecting region and the Franck-Condon factors leading region.Based on the above models,the methods to determine plasma parameters by OES are given.Besides,a set of software named HUSTCRM with CR model of atomic hydrogen,coronal model of molecular hydrogen and diagnosis of plasma parameters is developed.At the last part,the spectroscopic systems in HUST source are introduced.The work of this thesis can help to clarify the mechanism of negative hydrogen ion sources and also lay a solid foundation for the OES of hydrogen plasmas in HUST source.