A triggering mechanism for secondary arcs [railguns]

It is postulated that there is local change in the magnetic field, associated with the rail joint connections, which causes a variation in the breech voltage and in the J×B force applied to the armature. Experimental data suggest that this change in force can trigger secondary arcs. A model was developed for the breech voltage variation based on the length of the perturbed region, the magnitude of the local field in the vicinity of the joints, and the length and velocity of the armature. The model suggests that the magnitude of the perturbation at both the 4-m and the 8-m joints is about the same. However, a secondary arc is formed at the 4-m joint, but not at the 8-m joint. The significant difference in the two situations is that the armature length at the 8-m joint is half that at the 4-m joint. The scenario repeats itself at the 12-m and 16-m joints with the same results. It is concluded that the development of secondary arcs in the presence of local magnetic field variations is sensitive to the armature length