Simulation of magnetic field produced by RF antenna and cusp magnets for RF driven H- ion source

This paper present simulation results obtained using Opera-3D for magnetic field generated by an external RF antenna and permanent magnets for plasma confinement, dipole filter field and electron suppression field for RF based H- ion source. C-type ferrite cores were introduced around the antenna to enhance the multi-cusp magnetic field. The size and geometry of antenna was optimized to produce the maximum magnetic field at the Centre of the plasma chamber. The magnetic field generated by the antenna driven by 400 Amps current is 1200 Gauss peak near to the conductor body and ∼ 480 Gauss at the center of antenna. An Octa-pole multi-cusp permanent magnetic field with outer iron cylinder has been proposed to confine the plasma along the axis of cylindrical plasma chamber. Electrons with 5 eV energy were plotted to show confinement trajectories to see the effect of cusp leak width. The permanent magnet dipole filter field strength of ∼ 150 Gauss at the Centre divides the plasma into two zones i.e. hot and cold electron zones. Cold electrons are responsible for generation of H- ions by volume production. The extracted beam contains both electrons and H- ions. The electrons were deflected by the pair of dipole magnets with ∼ 330 Gauss field and dumped on the extraction electrode, by bending at 90 degree to the beam axis. The magnetic fields of the RF antenna and multi-cusp were optimized with computer simulation to help in optimization of H- ion beam extraction. (author)