Investigation on the spatial distribution of H⁻ ions in RF ICP source with Faraday shield

Abstract For the realization of magnetic confinement fusion, the negative hydrogen ions produced by an radio frequency (RF) ICP (inductively coupled plasma) source are employed for neutralization process of the neutral beam injection system. A 3D fluid model tailored for the RF ICP source has been developed to explore the negative hydrogen ion distribution. The negative hydrogen ion source consists of the cylindrical driver containing Faraday shield (FS) and the expansion chamber equipped with permanent magnets. The study is focused on the influences of FS, pressure (0.5–2.0 Pa) and permanent magnet remanence (0–1.03 T) on the negative hydrogen ions distribution. When the FS is applied in the driver, the negative hydrogen ion density is low owing to the high electron temperature. The maximum density of the negative hydrogen ions rises monotonically and shifts to the driver with the increased gas pressure. The distribution of negative hydrogen ions is dominated by transport processes at low pressures, while the collision processes become significant at high pressures. The density of negative hydrogen ions near the plasm grid increases with the transverse magnetic filter (TMF) strength as a result of the decreased temperature of electrons. The asymmetry in the density of negative hydrogen ion is enhanced with the increased TMF strength. Our current model offers valuable insights into the behavior of negative hydrogen ions within RF ICP source, thereby advancing our comprehension of this critical component in fusion engineering.