Modeling re-ionization and particle trajectories in the neutral beam injectors of the DIII-D Tokamak

J. P. HILDEBRAND, Whitworth University, B. J. CROWLEY, General Atomics. Neutral beam systems for plasma heating in fusion devices require a source of plasma from which to extract ions. These ions are accelerated by a series of grids at high potentials before they pass through a neutralizer and are recombined through collisions with a gas. After this, they are injected into the tokamak to impart their energy into the plasma. However, there are background gas molecules that can cause re-ionization for a portion of the neutral beam and in the presence of a magnetic field, the ions can be deflected into various beamline components and cause damage. Here we present the results of a modeling study where particles are tracked from the ion source until they are either injected into the tokamak or collide with a beamline component. The results are used to predict potential damage and recommend mitigating actions that may include administrative limits or engineering solutions.