Simulation of Electron Trajectories in the Multicusp Ion Source Using Geantn4 Monte Carlo Code

To optimize the negative ion source and generate intense beams of negative ions, understanding of transport properties of both electrons and negative ions is indispensable. Transport process of negative hydrogen ions (H⁻) in a multicusp H⁻ source, has been simulated by three-dimensional Femlab simulation software. Multipolar plasma confinement is known to result in enhanced plasma density, homogeneous plasma of a large volume, and quiescent plasmas. The effect of plasma confinement by applying multi-polar magnetic field was investigated. Results are obtained for ten different configurations of permanent magnet and discussed. Full line cusps are found to give optimum plasma density. Negative ions created on the sidewall hardly can reach the center of the source due to trapping by the multicusp magnetic field. As a result, H⁻ ions created on the sidewall do not have a significant effect on the H⁻ current.