Computational design of magnetic beamlet deflection correction for NNBI

Abstract Coextracted electrons are inevitable for negative ion based NBI systems. To avoid wastefully accelerating these electrons to the full energy, they are magnetically deflected out of the beamlet onto the extraction grid. The deflection of the electrons creates an unwanted deflection of the ions, which is magnetically corrected in the ITER heating neutral beam. In order to gain experience with magnetic deflection correction, IPP has designed a magnetic deflection correction system in collaboration with the ITER organization, which will be characterized in the BATMAN Upgrade test facility. The ion-optics code IBSimu is used for the design of the magnetic deflection correction system. A comparison of the design candidates shows that the magnetic deflection correction system inherently leads to an increased divergence as result of the magnetic field structure. The divergence increase manifests itself as an increased fraction of a broader halo component.