Computational Studies on an Induction Coilgun

Abstract

Induction coilgun works on the principle of electromagnetic induction between an array of coils, which are wound on a long insulating barrel of appropriate length, and an electrically conducting projectile placed inside the barrel. Previously charged high voltage capacitor banks are sequentially discharged into the coils through high voltage solid-state switches leading to the generation and flow of high magnitude impulse currents through the coils. Time-varying magnetic flux thus produced by the pulsed currents through the coils interact with the projectile inside and induce a resultant current on it. The electromagnetic force exerted on the projectile is a product of the excitation current through the coil (i <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> ), induced current on the projectile (i <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</inf> ), and the mutual inductance gradient (dM <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cp</inf> /dx, i.e., the change in mutual inductance between the coil and the projectile as the projectile travels through the coil). The induced current on the projectile depends on the level of magnetic coupling between the coil and the projectile, which is governed by their geometric property, viz., diameter, number of winding layers in the coils, and number of winding turns per layer of the coils; diameter, length, shape, and material of the projectile as well as the projectile’s position w.r.t. the coils as it moves along the barrel. In this paper, the following parameters, viz., number of winding layers of the coil, number of winding turns per layer of the coil, and the projectile length are varied, keeping the pulsed power source (PPS) parameters as well as the projectile’s outer diameter and mass fixed. The analysis is performed using a commercially available Finite Element Method (FEM)-based software, Ansoft Maxwell. Results obtained from the analysis are used to design and develop a two-stage induction coilgun in the author’s laboratory.