Augmentation of Current Ramp-Down Contact Pressure in C-Shaped Armature Railguns

It is necessary to maintain adequate contact pressure between a rail and an armature to avoid transition in a solid armature railgun. The contact pressure of the C-shaped armature at start-up arises from its initial mechanical interference. As armature wear grows and temperature rises, the initial mechanical interference decreases. When the current is established, the electromagnetic (EM) force provides the contact pressure. Transition usually occurs when the current ramps down, except for relatively light situations that have low currents and speeds. In this paper, launch experiments with armatures of the same geometry and material under different driving current amplitudes were performed. Based on the experimental results, the temperature rise of the armature with increasing action was analyzed. Then, the preload during the period of temperature increase was analyzed. In a simplified model, the EM force was also analyzed. The results indicate that the sum of preload and EM force has shown a decreasing trend. To reduce the consequence of EM force that decreases with current ramp-down, a partially augmented railgun, which could maintain adequate contact pressure in current ramp-down, is proposed. The feasibility of this kind of railgun is also analyzed.