Optimization of negative ion extractor in a JAERI 400 keV H[sup -] ion source.

The influence of a dipole magnetic field in the extractor on the beamlet deflection has been investigated using a JAER1400 kev H- ion source. The beam deflection angle decreased from 10.2 to 7.0 mrad when the integrated value of the magnetic field was changed from 2530 to 910 Gcm. The measured deflection angle was larger than the estimated value from the ion trajectory considering the magnetic field. To understand the dominant factor that enhances the beam deflection angle, three-dimensional trajectory simulation was performed. It was confirmed that the axis of the beamlet deflected by the magnetic field in the extractor is displaced from the center of the aperture at the grounded grid (GRG). This displacement enhances the beam deflection angle due to the effect of the electrostatic lens at the GRG. This phenomenon is similar to the beam deflection by aperture displacement of the GRG. [ABSTRACT FROM AUTHOR]