Fully electromagnetic particle‐in‐cell simulations of Applied‐Bion diodes have been performed using themagiccode. These calculations indicate that Applied‐Bdiodes can be nearly 100% efficient. Furthermore, the simulations exhibit an impedance relaxation phenomenon due to the buildup of electron space charge near the anode which causes a time‐dependent enhancement of the ion emission above the Child–Langmuir value. This phenomenon may at least partially explain the rapidly decreasing impedance that has been observed in Applied‐Bion diode experiments. The results of our numerical simulations will be compared to experimental data on Applied‐Bion diodes and to analytic theories of their operation.