Analysis of ion beam optics of tetrode accelerator for neutral beam injector on the experimental advanced superconducting Tokamak

The ion optics is very important for an accelerator. The tetrode accelerator with slot apertures was employed on the neutral beam injector (NBI) for the Experimental Advanced Superconducting Tokamak (EAST). The ion optics of ion source accelerator was simulated using the IGUN code. The results have shown that the accelerator with diamond cross section plasma grid can get lower divergence angle comparing with the one with circular cross section plasma girds. In this paper, the voltage applied on the gradient grid (80%, 83% and 86% of plasma grid voltage) and the gap between plasma grid and gradient gird, gradient grid and suppression grid were also changed to estimate the ion extraction efficiency and ion beam trajectory. The results are helpful for the development and optimization of EAST-NBI ion source.