This chapter introduces some potential applications of ion beam in high-current ion linacs, and discusses two key issues in such applications including the formation mechanisms of beam halo-chaos and its control methods. It is known that ion beam halo-chaos can be generated via different mechanisms, and recently some successful feedback methods have been developed for halo-chaos control, such as nonlinear feedback control, wavelet-based feedback control, switching manifold methods and time-delayed feedback self-control. Both analytical and numerical results have shown that these control methods are effective for suppressing beam halo-chaos.