A bstruct-Rail guns generate electromagnetic signatures that contain frequencies extending from quasi-dc to tens of kHz.The c h a r a c t e r i z a t i o n of these fields for electromagnetic compatability concerns remains, however, largely unexplored. Accordingly, this paper includes a discussion of the theoretical models used to predict the inductance gradient, the transient behavior of the currents produced in the rail gun structure, the dynamical generation of the external fields, and a comparison of the theoretical model with experimental data.The predicted rail inductance gradient of LL = 0.52 p H / m compares very well with the measured value of 0.522 p H / m . The existence of an inductance gradient efficiency factor, E,,, is demonstrated, with a derived value of 0.75. This produces an effective inductance gradient of L' = E ,,LL = 0.39 p H / m which leads to a predicted muzzle velocity of 525 m/s that is within 5% of the measured value.Predicted magnetic field waveshapes a r e in good agreement with observations close to the bore center.For radial distances greater than a foot, measured peak fields exceed predictions by a factor of two to three. This issue is being investigated. a limited comparison with experimental data. Companion paprs by Cobum et al. [1]-[2] address the observations and experimental configuration in detail.The incorporation of a rail gun into a weapon system requires a quantification of the relationship between the power source, rail gun dynamics, and electromagnetic fields generated by the rail and armature currents. In order to ensure EMC with other equipment, it is necessary to not only characterize the dominant low-frequency (dc to tens of kHz) fields generated by the moving armature, but also the higher frequency emissions generated by continuum arcing along the rails, and the larger arc produced at the muzzle.For predicting the low-frequency magnetic fields it appears that the circuit approximation to the rails, which has traditionally been used to study armature acceleration, is probably adequate. On the other hand, a modal analysis of the rail system model viewed as a transmission line is required at higher frequencies in order to model arcing contributions. In addition, it may be necessary to incorporate the effects of electromagnetic shielding in the evaluation of EMC for an actual system. This paper is the first in a series of reports that eventually will quantify EMC considerations for all frequencies of interest. We concentrate at present only on the low-frequency fields generated by the rail current in a solid mature, for which there is negligible arcing.
CONCEPTUAL ISSUES AND OVERVIEW