Effects of the weak magnetic field and electron diffusion on the spatial potential and negative ion transport in the negative ion source

A two-dimensional electrostatic particle simulation was performed for investigating the effects of the weak magnetic field on the negative ion extraction in a negative ion source. The motion of the charged particles was simulated in their self-consistent electric field using a particle-in-cell model. A simple random-walk model determined the effect of the electron diffusion across the weak magnetic field. The weak magnetic field magnetized most of the electrons some of which were lost along the field line. In a region close to the plasma grid, more negative ions arrived instead of electrons for ensuring plasma neutrality.