Fig. 1. Basic flow chart of the numerical simulation with IBSimu code

Fig. 2. Structure of negative ion source of CRAFT NNBI

Fig. 3. Aperture structure and voltage relation of the negative ion source for CRAFT NNBI

Fig. 4. Trajectories of negative ions (red line) and electrons (yellow line) during extraction and acceleration under different ion current densities

Fig. 5. Characteristics of the beamlet divergence at the GG aperture exit under different extracted current densities

Fig. 6. Characteristics of the beamlet divergence at the GG aperture exit under different simulation conditions

Fig. 7. Characteristics of the beamlet divergence at the GG aperture exit under different acceleration gaps

Fig. 8. Character of the beamlet divergence at the GG aperture exit under different extraction gaps