Analysis of the Differences in the Optimum Triggering Positions and Projectile Velocities in Multistage Induction Coilguns for Different Arrangements of the Drive Coil Current Directions

The direction of the excitation current through the drive coils (or simply the coils) of the successive stages in a multistage induction coilgun can either be maintained the same (i.e., same direction) or reversed alternatively (i.e., alternating direction). The optimum triggering position of the armature (or the projectile) inside each stage coil changes accordingly in these two launcher configurations to achieve the highest muzzle velocity, which is also different for these two launcher configurations. This article presents a finite-element method (FEM)-based analysis on the differences in the projectile’s optimum triggering positions inside each stage coil and the achieved muzzle velocities for the same and the alternating directions of the drive coil currents in a four-stage induction coilgun. The reasons for the differences in the projectile’s optimum triggering positions inside each coil for the two launcher configurations are explained in this article in two ways: 1) by comparing the mutual inductance gradients between the projectile and each coil of the two types of launchers as the projectile travels from coil 1 to coil 4 and 2) by comparing the optimum propelling force profiles of the projectile in both types of launchers. Furthermore, this article shows that the muzzle velocity of the projectile increases by alternatively reversing the direction of the excitation current through the coils of the successive stages in a multistage induction coilgun rather than maintaining the current in the same direction. The reasons behind the enhancement in muzzle velocity are explained in this article by analyzing the armature capture effect and active duration of the accelerating force on the projectile for the two types of launcher configurations.