Effect of rail/armature geometry on current density distribution and inductance gradient

The distribution of current in the conductors which is affected by the geometry of the armature and the velocity of the armature plays an important role in the performance of an electromagnetic launcher. In the early launching stage the current tends to flow on the outer surfaces of the conductors, resulting in high local current densities. Later in the launch, the tendency for current to concentrate on the surface is driven by the velocity skin effect. High current densities produce high local heating and, consequently, increased armature wear. This paper investigates the effects of rail/armature geometry on current density distribution and launcher inductance gradient (L'). Three geometrical parameters are used to characterize the railgun systems. These are the ratio of contact length to root length, relative position of contact leading edge to root trailing edge, and the ratio of rail overhang to the rail height. The distribution of current density and L' for various configurations are compared.