Inductance Gradient Variation With Time and Armature Sliding Along the Rails

The inductance gradient is one of the important parameters on the design and evaluation of railgun performance. The size, shape, and material of rails have effects on the inductance gradient. In 2-D analysis, the length of rails assumed to be infinite and then the effect of the armature ignored and a constant inductance gradient is obtained. In 3-D simulations, with assuming a fixed position for the armature (usually in the middle of rail), the inductance gradient can be determined. However, with the moving of the armature along rail length and the increasing of the current path, the applied force on the projectile will be different when it is constant and in the middle of the structure. Therefore, inductance gradient in the structure length will be changed. In this paper, with considering a railgun with copper rails with 1-m length, according to the input current and the resultant force of the aluminum armature in the rail length it was displaced in every step, the inductance gradient was determined. The results show that the amount of inductance gradient is not constant and will be increased with armature movement toward the muzzle.