The Study Of Plasma Excitation Characteristics Of RF Ion Source

Neutral beam injection(NBI)is one of the most efficient means of four auxiliary plasma heating means in controllable nuclear fusion physics studies,and it has the most clearest mechanisms and highest plasma heating efficiency.The high current ion source is one of the key components of neutral beam injector,its reachable performance determines the achievable targets of the EAST NBI.The hot cathode bucket ion source was designed and developed on the EAST-NBI system.Comparing with the conventional hot cathode ion source,the absence of filaments,simpler mechanical structure,convenient maintenance and longer lifetime are the the most significant advantages of radio frequency(RF)sources.For the purpose of satisfying long pulse operation and the future demands of high energy ion source of NBI,the RF ion source was developed and studied.Firstly,in this paper,the present research status of RF ion sources at home and abroad are deeply investigated.On the basis of this,the criterion of gas breakdown of RF discharge and the effect of two electric fields generated in the discharge chamber are analyzed.Secondly,the related simulation research of the generation characteristics of RF plasma were carried out according to the selected physical model.The distribution of electron density,electron temperature,plasma potential,the relationship between electron density and plasma potential,skin effect are analyzed.The influence of the structural parameters such as the number of turns,the inter-turn spacing and the diameter of the driver on the plasma discharge is studied emphatically.Based on the simulation results and the actual requirements,the structural parameters of the final EAST NBI RF ion source are determined.Then,the influence of RF power and discharge gas pressure on plasma parameters are studied based on the structure model of EAST NBI RF ion source.At last,the experiment research on plasma excitation characteristics are carried out on the existing test platform of NBI RF ion source.The influence of discharge gas pressure,RF power on electron density and electron temperature are studied by the electrostatic probe.And the water flow calorimetry system is used to measure the temperature rise of faraday shield,coils and other components,the power deposition distribution of each component in the process of radio frequency discharge is obtained and analyzed.The development of this subject has laid a certain theoretical and experimental foundation for the development of EAST NBI RF ion source,and provided some reference for further optimizing the structure of RF ion source.