New methods of direct-energy conversion from energetic ions through the interaction between ions and electromagentic fields (i.e., Peniotron-type and Gyrotron-type converters,) were proposed, and the performance characteristics of the former are presented in this study. Numerical analyses have shown that the Peniotron-type converter has excellent performance characteristics in energy recovery from the energetic ion energy associated with the velocity component perpendicular to the axially applied magnetic fields in the converter, where ions make helical motions. The energy recovery efficiency is found to be dependent upon the energy spread, the incident angle, and to the deviation of the gyration center from the converter axis at its inlet. Control of the gyration center, in particular, is found to be most important. The analyses have shown that the new methods are essentially feasible in recovering energy from 14.7-MeV protons in a D-3He advanced fusion reactor with high efficiency.