[en] Particle simulations of diode gaps with applied voltages using the 2-D electromagnetic code MAGIC have been done for a variety of configurations and applications. Under some conditions, the system is found to be electromagnetically unstable. These instabilities may be useful, as in the magnetron or emitron microwave generators, or detrimental, as in magnetically insulated sheaths or certain ion diodes. In this report, we discuss the present status of this work and indicate how the code output compares with the results of theory or experiment, in cases where such results exist. Some problems have also been studied with the 2-D quasistatic codes, and we discuss the differences between these results and those of MAGIC