Effect of driving current profile on acceleration efficiency of electromagnetic railgun

In this paper, the effect of driving current profile on efficient utilization and conversion of stored electrical energy into kinetic energy of the projectile has been investigated for electromagnetic railgun systems. It has been experimentally evidenced and also corroborated by simulation results that the acceleration efficiency of railgun launcher is much higher for the case when the driving current feed has an over-damped unidirectional profile vs the case when an under-damped sinusoidal current of same amplitude is fed. To analyze this effect, a mathematical model has been developed incorporating dynamic resistance scaling and velocity dependent frictional effects. For the typical case of projectile weighing ∼8 g and input driving current amplitude of ∼220 kA, the estimated average force from the mathematical model simulation acting on the armature projectile increases from 1.4 to 3.83 kN, consequently resulting in an increase in velocity from 489 to 931 m/s and overall efficiency from 0.55% to 2% for the sinusoidal and unidirectional current profiles, respectively. Experimentally, a maximum velocity of ∼1024 m/s was obtained when a unidirectional over-damped current of similar amplitude was fed using a pulse shaping inductor in conjunction with a crowbar switch. The obtained experimental results of trials with different masses of armatures complement the results of the conceived mathematical model used in simulations. The marginal underestimation of the simulated velocity is due to the inevitable lacking in precise estimation of the frictional force and mass loss that dynamically occur in the projectile during acceleration.