Simulations of negative ion extraction from a multi-aperture ion source in the presence of the magnetic filter

The particle-in-cell method based numerical model of negative ion beam extraction from a large volume multi-aperture ion source is briefly described. The model takes into account the influence of the transversal magnetic field and diffusion of electrons across the field. The current-voltage curves for H- ions and electrons are presented. The results are compared for the three cases: without filter field; with the field but without diffusion; and with the field and electron diffusion. The presence of the magnetic filter field increases H− yields significantly (by 200%). A random-walk electron diffusion model enables electrons to travel through the magnetic field, which reduces a nonphysical effect of excessive electron aggregation in the filter region. The changes of filter width do not alter H− current more than 10%.