Reinforcement of the Magnetic Lens Effect in the Dipole Magnet for a Neutral Beam Injector

Dipole magnet for a neutral beam injector is a magnetic device deflecting residual ions to an ion dump. For the high power neutral beam injection to fusion plasma, the heat load on the surface of the residual ion dump should be under acceptable level. We investigate the magnetic lens effect of the bending magnet for beam expansion cases. To intensify the magnetic lens effect, the height of the field clamp in the magnetic core is adjusted. The COMSOL Multiphysics software is employed to calculate a magnetic flux density for the dipole magnet, to trace an ion beam trajectory, and to evaluate a heat distribution on the beam dump. Simulation results reveal that the longitudinal magnetic field at the magnet entrance has a significant effect on the heat distribution in the ion dump surface, and hence the local heat flux is considerably alleviated by the field clamp with adjusting the height of the clamp.