Numerical Simulation Of Surface Production And Extraction Process Of H~-ion In High-power Negative Hydrogen Ion Source

Large magnetically-confined fusion devices,such as ITER(International Thermonuclear Experimental Reactor)require NBI(Neutral Beam Injection)systems for heating and current drive.In order to penetrate into the fusion plasma core and provide an efficient current drive,neutral beams with a particle energy of 1 Me V are required.At such a high energy,the neutralization efficiency of positive hydrogen-ion beams tends to zero,while it is still 60 % in case of negative hydrogen ions.So negative ion beams will be used to produce the neutral beams.There are two kinds of sources used in the NBI system for ITER,RF negative hydrogen ion source and arc discharge filament source.Compared with the arc discharge filament source,the RF negative hydrogen ion source does not require the regular filament replacement,so it has basically maintenance-free operation and will be operated remotely during the ITER discharge.In 2007,the ITER board has decided to adopt the RF driven ion source as the reference source for the ITER NBI.Recently,China has also to start various studies on RF negative hydrogen ion sources such as in the CFETR(China Fusion Engineering Test Reactor).The structure and principle of negative hydrogen ions source are very complex.There are still some unsolved issues,such as the surface creation process of hydrogen negative ions,the optimal design of the extraction system and the analysis of the extraction beam.This thesis focuses on the negative hydrogen ion source project of Huazhong University of Science and Technology(HUST),and studies the surface generation and extraction of negative hydrogen ions by theoretical analysis and numerical simulation.The main content of the thesis is divided into four parts:The first part focuses on the theoretical foundation,introduces the mechanism of surface production and extraction of negative hydrogen ions,and gives the corresponding numerical methods,including the Particle-in-cell Monte Carlo collision(PIC-MCC)algorithm and Vlasov-Poisson iteration algorithm.The second part focuses on the numerical study of the surface production of negative hydrogen ion.This part presents the ion-ion inverse sheath structure and explain the experimental phenomena in the negative hydrogen ion source with this sheath model.The result implicits that increaseing the density of positive ions can increase the extraction efficiency of negative hydrogen ions source.In addition,the cause of the instability of the ion-ion plasma was analyzed using the structure characteristics of ion-ion inverse sheath.The third part focuses on the numerical study of the extraction system.A simple model of Child's law is used to verify the correctness of the whole program,which considered the space charge effect,and the error of simulation is analyzed.In the simulation,the method of adding new nodes is used to simulate the electric field of complex extraction system,and a simulation case of the electric field of the extraction system is demonstrated to verify the accuracy of this method.The fourth part focuses on the analysis of the extraction beam quality of negative hydrogen ions.The main factors affecting the extraction beam parameters are analyzed,such as the deflecting magnetic field and the extraction voltage.Under the given plasma parameters and the structure of the extraction system,the optimal extraction voltage and deflection magnetic field are obtained.This will provide guidance for the engineering design of extraction system of the negative hydrogen ion source driver built by HUST.