A Plasma Trap as a Target for Neutralization of the Negative Ion Beam

For neutralization of the H^- beams with an energy of 1 MeV, it is reasonable to use plasma targets with the yield of atoms much higher than that in gas targets. The target plasma is proposed to be confined in a magnetic trap with weak longitudinal magnetic field, the inverse plugs and circular multipole walls. Because of conservation of canonical angular momentum in the axially-symmetric system, the longitudinal confinement of particles by inverse plugs is rather hard. Transversal confinement of plasma is rather good. The target plasma is proposed to be generated by the 100-200 eV electrons.

A possibility to develop the experimental plasma target with a 10 cm aperture is considered for neutralization of the H^- ion beam with a current up to 2 A. A magnetic field is planned to be formed by circular NdFeB magnets and iron screens. Results are given of the computer simulations for the magnetic system and its optimization for the plasma confinement and especially for restriction of its escape through the end wall holes. Numerically calculated trajectories of the ensemble of plasma electrons with various initial coordinates and trajectories of beam ions are given.