[en] The Autoresonant Accelerator (ARA) offers great promise for collective ion acceleration provided large amplitude cyclotron waves can be generated with long coherence scales and controllable propagation characteristics. Numerical simulations have been performed to examine cyclotron wave growth in a helical slow-wave structure. No inhibition of growth was observed, short of an intrinsic space charge limitation. Extraction of such waves from the amplifying section through realistic terminations has been performed. The radial structure and propagation of these large, extracted cyclotron waves has been studied and comparisons with linearized waves have been drawn. The effect of nonlinear wave properties on ARA designs are presented