Three-dimensional fluid simulation of radio-frequency negative hydrogen ion source with the addition of noble gases

Abstract As an essential part of the neutral beam injection system for the magnetic confinement fusion devices, radio-frequency (RF) ion source is responsible for generating negative hydrogen ions. The addition of argon and xenon is an alternative approach to enhance the volume generation of negative hydrogen ions. A 3D fluid model of RF negative hydrogen ion source is developed to investigate the effects of adding argon and xenon gases on the spatial distributions of electron density, electron temperature and negative hydrogen ion density. The 3D fluid model is validated by comparing the numerical results with experimental results in pure hydrogen discharge. With the addition of argon and xenon, the electron density increases and the electron temperature reduces due to their low ionization threshold energy and large electron impact ionization cross section. Additionally, the results show that the largest enhancement of negative hydrogen ion density at the bottom of expansion chamber is achieved under the xenon admixture fraction of 20% and gas pressure of 0.3 Pa, exhibiting an increase of 1.6 times compared to pure hydrogen discharge. The model can be applied for the optimization of RF negative hydrogen ion source.