AN EMPIRICAL-MODEL FOR PLASMA ARMATURE VOLTAGE

Scaling of armature voltage with bore diameter is an important issue since it affects the predicted efficiency and the predicted velocity performance of proposed large-bore EM launchers. In this paper the experimental data for railguns with plastic/composite insulation is shown to fit a scaling relation of the form V(m) - V(e) + E (i) d, where the electric field dependence on current density is given by E(i) - E(a) + j/d. This scaling relation prodices a linear increase in armature voltage with bore diameter for d > 0.1 m. The model is in better agreement with the limited data on large bore railguns than earlier models.