Static and quasi-static models for the magnetic field of a railgun

A computational model for the electromagnetic (EM) environment generated by a railgun is of interest for considering EM effects on electronic circuits early in the design phase. Static models are used to investigate the magnetic (H-) field of current-carrying conductors. The quasi-static H-field, for a filament rail current, is compared to experimental data for a railgun shorted at the muzzle. Quasi-static or dynamic models are required to predict the transient H-field associated with an accelerating armature, which require determining the force on the armature. The transient H-field for current filaments is calculated assuming either a constant armature acceleration (i.e., DC rail current) or a time-varying acceleration. In both cases the model is quasi-static in that the transient H-field is calculated from the rail current waveform. Good agreement with experimental data is obtained close to the rails. The effect on the H-field of an efficiency factor, to account for that part of the rail inductance involved in the armature acceleration process, is demonstrated. The results indicate that a filament current model with a quasi-static armature acceleration provide an engineering tool for transient EM environment predictions.<>