To clarify the physical mechanism of the plasma spatial nonuniformity observed in tandem-type negative-ion sources, the primary electron-transport process has been analyzed by a three-dimensional Monte Carlo simulation code. In the model, equations of motion for electrons are numerically solved. The realistic geometry and magnetic-field configuration are taken into account. Various collision processes with neutral particles are also included in the model. The simulation results show that (1) the primary electrons have been lost from the source region to the extraction region due to the magnetic drift in the filter magnetic region and (2) the magnetic drift velocities have opposite directions near the sidewalls. The effect of the magnetic drift is one of the possible causes to explain the spatial nonuniformity observed in the experiment.
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