Preliminary design of an augmented railgun: Influence of the dimensions of the outer rails on the forces acting on the projectile and the rails

For the preliminary design of an augmented railgun, the electromagnetic repulsive forces on the rails and the self and mutual inductance gradients were determined by simulation. This design is meant for the realization of an augmented railgun at the French-German Research Institute in Saint-Louis, France. The simulated railgun has a 25 mm × 25 mm square calibre and both the inner and outer rails have a rectangular cross-section. In our study the geometry of the inner rails is fixed while the dimensions of the outer rails were altered. A 2D transient analysis for the determination of the magnetic forces on the rails was carried out with the finite element method program ANSYS. The EM force on the projectile is analytically calculated with the force-equation based on values of the inductance gradients determined with 3D AC-analyses. The influence of the ratio between the currents in the inner and outer rails on the electromagnetic forces has also been investigated. We have shown that the EM force acting on the projectile increases when the height of the outer rails and the distance between the inner and outer rails decrease. However this also leads to higher repulsive forces between the rails. For the theoretically best geometry, based on the electromagnetic forces, a 3D transient analysis was carried out. The electromagnetic force determined directly with the 3D transient analysis is then compared with the one obtained with the analytical method. A good agreement was found.