Effect of Rail Tapering on the Inductance Gradient Versus Armature Position by 3D-FEM

Abstract

The increasing of projectile final velocity and the uniformity of current density in the special regions of the armature and rail such as the root of the armature which is in melting are some of the purposes of the railgun design. In railgun, the applied force to run an armature is resulted from the interaction of the current passing from the armature with the magnetic field in that place. Therefore, to increase the running force and gain bigger projectile velocities, we have to increase the input current or the magnetic field between two rails per a constant current. The increasing of input current can cause more heat losses in the structure of the railgun and may cause failing of the projectile procedure because of the melting of some points of the armature or rail. High magnetic fields between rails without input stimulation increasing are possible with the application of the geometrical and structural variations in rails. The current paths in rails will be closer to each other (increasing the amount of magnetic fields between them), and so, narrowing the rail using a constant current, the current density will be bigger in the cross section of the rail. We will evaluate the effect of rail narrowing in the projectile path length with consideration of a rail length of 1 m. The narrowing procedure of the rail is defined as decreasing its cross section in the projectile path length until, in the output gate, its amount reaches zero (the height of the rail is constant). The result of simulation shows that the gradient inductance will be increased with the narrowing of the cross section of the rail in the projectile path length, and this will increase the amount of the final projectile velocity.