The focusing properties of an Inverse Reflex Tetrode (IRT) used for ion beam generation have been investigated experimentally. Focusing is achieved by replacing the planar (0°) electrodes of a standard IRT with moderately inwardly tapered electrodes (7.5, 10, and 15°). The greatest degree of focusing is obtained with the 15° electrodes as determined by beam profile measurements using streak photography and nuclear activation techniques at various axial target positions. A scissoring effect is observed, due to temporal variations in generator voltage and current, that is manifested by an axial variation in the focal point with time. Calculations of proton trajectories confirm the experimental results and demonstrate the importance of self‐fields within theA‐Kgap in determining the characteristics of an ion beam generated by an IRT.