Characteristics of Electromagnetic Radiation of a Railgun at the Final Firing Stage

Abstract

The navy railgun prototype propels its projectile with Lorentz force and is capable of delivering $\sim $ Mach 7 speed for $\sim 15$ -kg projectiles. The source of the Lorentz force is a gigawatt-class pulsed power supply (PPS) that delivers $\sim 1$ MA current with $\sim 10$ kV voltage into the railgun load. The energy efficiency of the railgun is usually less than 40%: a considerable amount of energy is released as heat, and a small amount as electromagnetic energy. The electromagnetic radiation of the railgun, although mostly shielded by its metallic cover before firing, may leak out at the final stage when the projectile leaves the barrel and can be a potential electromagnetic compatibility issue for onboard electronics. We analyze the electromagnetic (EM) radiation coming from the rails and armature of the railgun with commercial software using the multilevel fast multipole method or higher order basis functions in the method of moment and evaluate the effects on electromagnetic radiation by adding one key component at a time in four models. Three field probes are set up 10 m from the muzzle, and four near fields are plotted on top of the muzzle. The near-field intensities and far-field radiation patterns at the final firing stage are presented and the frequency response is simulated. We found that most far-field patterns are directed toward the breech direction due to impedance mismatch between the PPS and railgun, and $E$ -field probes show stronger intensity on the $z$ -axis. Outer metal casing helps concentrate the electromagnetic energy inside the gun, and dielectric material absorbs the field within. The $E$ -field inside the gun is well below the breakdown threshold of common dielectric insulators. Strong radiation may occur if the railgun voltage spectrum contains a large megahertz component.