In this article, a general study of diffusional effects is made numerically as well as theoretically with the aim to reproduce not only the current scaling of ion diodes but also the divergence of the ion beam and physical features such as virtual cathode movement due to the diamagnetic effect. It has been observed experimentally that the ion current exceeds that quantity which would be expected in the presence of a strong magnetic field. It is demonstrated that with the introduction of a diffusional fieldE&thgr;into the stationary 21/2‐dimensional particle‐in‐cell code based on boundary‐fitted coordinates [T. Westermann, Nucl. Instrum. Methods A263, 271 (1988)] the simulation results agree well with experiment. Thisadhocmodel is supported theoretically by linear stability analysis of the stationary state.