Railgun electric fields: theory and experiment

Experiments were conducted and related three-dimensional theoretical predictions were made to identify sources of the electric field (E-field) near the ARL 15 mm and 50 mm square-bore railguns during the pulse discharge. This work was undertaken to better understand the results of earlier studies which reported measured E-field pulse shapes that resembled the muzzle voltage but whose magnitudes were much larger than those predicted on the basis of quasi-static currents flowing only in the rails and armature. In these experiments, an armature was stationary in the bore of the railgun while the E-field was measured. Peak currents for the 15 mm and 50 mm bore railguns were 72 kA and 233 kA respectively. Two types of E-field probes were used to provide the measured data. The transient E-field data were measured at various locations along the length of the rail and with and without the power supply shorted at its output. As such, the dominant features of the E-field attributable to the coupling of the railgun with the breech and power supply could be identified. Based on the analytical predictions and the measured E-field data, it is suspected that the high E-fields were caused by current sources within the power supply and railgun breech conductor systems.