Experimental and Computational Studies on the Efficiency of an Induction Coilgun

Armature design plays a significant role in determining the performance of an induction coilgun. In this article, aluminum projectiles of 10.5-mm length and 21.7-mm outer diameter but of different shapes and thicknesses are fired from different initial positions inside the barrel having an outer diameter of 25 mm and a thickness of 1.5 mm with the coil wound over it. The coilgun is powered by charging a 504-μF capacitor bank up to 800 V and discharging it through the coils of a three-stage induction coilgun. Experiments are also performed at different initial charging voltages of the capacitor bank. For each firing, muzzle velocity of the projectile and efficiency of the induction coilgun are studied. Positions and muzzle velocities of the projectiles are measured using infrared sensors. A maximum muzzle velocity of 23.86 m/s with a projectile of mass 2.8 g and a maximum efficiency of 0.76% with a projectile of mass 8.5 g have been achieved with the present hardware setup in the laboratory. Experimental results are analyzed using the transient solver of the commercial software, ANSOFT Maxwell. From the analyses presented in this article it is found that the projectile having the highest muzzle velocity has a thickness equal to the skin depth and has a uniform current density distribution along its thickness as well. This article concludes that projectile thickness being equal to the skin depth of the projectile results in significant increase in its muzzle velocity and reduction in its mass which is an important design consideration of the induction coilgun. Secondly, each projectile has an initial firing position which is the best to achieve the highest muzzle velocity i.e., the highest efficiency of the induction coilgun and this position depends on the dimension and shape of the projectile.