An empirical model for plasma armature voltage (in EM launchers)

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 electromagnetic launchers. The experimental data for railguns with plastic/composite insulation is shown to fit a scaling relation of the form V/sub m/=V/sub e/+E(j)d, where V/sub m/ is the muzzle voltage, V/sub e/ is the total electrode drop, and the electric field dependence on current density is given by E(j)=E/sub 0/+j/ sigma . This scaling relation predicts 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.>