System Design And Analysis Of High Power RF-driven Negative Ion Source

Fusion energy is considered to be the most promising solution to the energy issue in future,and has been paid attention worldwide.The basis of Neutral beam injection(NBI)is the injection of the high-energy neutral beams into the fusion plasma.Ion sources are the core components of NBI systems,and radio frequency(RF)driven negative ion sources with high power and high current are recognized as the best choice for NBI systems in International Thermonuclear Experimental Reactor(ITER)and other future large-scaled fusion reactors.Huazhong University of Science and Technology(HUST)has carried out the project “Research of the key techniques of ITER RF negative ion sources” under the support of Ministry of Science and Technology of China since 2011.A RF driven negative hydrogen ion source experimental setup without extraction system has been built successfully.In the thesis,the RF driver of the experimental setup is researched.Based on the setup,the key technologies of negative beam extraction are investigated in detail,and a whole RF negative ion source is designed.The design of the negative ion source faces following challenges:(1)Design of the RF negative ion source.Negative ion source is an intricate facility,which includes RF driver,caesium oven,extraction system,diagnosis system and other components.In addition,information about the development of a whole RF negative ion source has not been reported in China.(2)Beam optics of extraction system.The structure and electromagnetism parameters of extraction system are critical to the beam performance.The extraction system should be designed carefully via the beam optics analysis.(3)Thermo-mechanical analysis of extraction system.The Faraday Screen and extraction grid would suffer high heat powers in operation.Hence,their cooling systems need to be designed to obtain a precise control of the temperature.(4)Stability of RF driver.RF driver operated with high power and long pulse is more likely to be broken down.It needs to be resolved urgently that how to improve stability of RF driver by increasing the RF power transform efficiency.(5)The design of vacuum and high voltage systems.Negative ion source is a complete and scientific engineering facility,which include water,electricity and gas subsystems.The design of vacuum and high voltage are especially important according to the special requirements.This thesis focuses on problems mentioned above,and aims to negative beam extraction.In the thesis,combined electromagnetic analysis,beam optics analysis,three phases coupling analysis and vacuum design,HUST RF negative ion source has been researched and designed.The main research contents are as follow:(1)Design of HUST RF negative ion source.According to the design requirements,HUST RF negative ion source is designed.RF driver,caesium oven,extraction system and diagnosis system are researched in detail.(2)Beam optics of extraction system.Aimed at the design parameters,an extraction system is designed with three grids.Beam optics analysis is carried out by particle tracking.By comparing the beam divergence angle,the geometry of grids,extraction voltage and deflection magnetic field are researched,to determine their effects on the beam performance.(3)Design and optimization of extraction system and RF driver.Plasma grid of the extraction system is operated with high current and high temperature.A simplified grid model is developed by the analysis of temperature and filter magnetic field.Extraction grid is the most critical,and is designed with a two-curved cooling system.Faraday Screen is also researched by thermo-mechanical analysis in this thesis.Two different cooling systems are designed with their applicable conditions.(4)Impact of RF driver structures on the RF power-coupling factor.RF power-coupling factor,which represents the transform efficiency from RF power to plasma power,is presented in this thesis.The requirement of RF power is expected to reduce by increasing the factor.Different structural drivers are researched the impact of structures on the coupling factor,and on this basis,we have provided some suggestions for the structures of RF drivers.(5)Vacuum and High-voltage design of negative ion source.The design of vacuum system and high-voltage system of HUST negative ion source are emphasized in this thesis.Pressure distributed differently between driver and backward chamber need to be achieved through the optimizations of the vessel and the vacuum pump.High-voltage system is considerd to insulate the driver,expansion chamber,extraction powers and other devices.Based on the research results of this thesis,the design of HUST RF negative ion source has been finished.All the components are under manufacturing,and expected to be assembled and adjusted in the first half of 2018.This source will be an experimental facility for further research of negative ion sources in the future.