Boundary-layer effect on railgun muzzle voltage

Measured values of railgun muzzle voltage exceed those predicted from simple armature models by several tens of volts. This excess voltage is called the contact potential and may represent a substantial fraction of the power dissipated in the armature. A simple two-dimensional model for the conductivity and velocity boundary layers has been used to calculate the electric field in the region near the rail surfaces. Calculations were performed for parameters characteristic of the University of Tennessee Space Institute (UTSI) 1-cm square-bore railgun. These calculations showed that the electric field decreased across the boundary-layer thickness and predicted contact potentials from 12.5 to 88.7 V, depending on the choice of boundary-layer parameters