3D fluid model analysis on the generation of negative hydrogen ions for negative ion source of NBI

A radio-frequency (RF) inductively coupled negative hydrogen ion source (NHIS) has been adopted in the China Fusion Engineering Test Reactor (CFETR) to generate negative hydrogen ions. By incorporating the level-lumping method into a three-dimensional fluid model, the volume production and transportation of H⁻ in the NHIS, which consists of a cylindrical driver region and a rectangular expansion chamber, are investigated self-consistently at a large input power (40 kW) and different pressures (0.3–2.0 Pa). The results indicate that with the increase of pressure, the H⁻ density at the bottom of the expansion region first increases and then decreases. In addition, the effect of the magnetic filter is examined. It is noteworthy that a significant increase in the H⁻ density is observed when the magnetic filter is introduced. As the permanent magnets move towards the driver region, the H⁻ density decreases monotonically and the asymmetry is enhanced. This study contributes to the understanding of H⁻ distribution under various conditions and facilitates the optimization of volume production of negative hydrogen ions in the NHIS.