Parametric Study of Possible Railgun Radiation in Postfire Stage

Abstract

Railgun represents a game-changing weapon for the U.S. Navy, with its development approaching maturity; the electromagnetic (EM) compatibility with other onboard electronics is becoming interesting. Railgun is powered by a gigawatts class pulsed power supply, and due to the nature of its design, considerable remnant energy is still applied to the railgun when the projectile leaves the barrel. If the plasma or debris formed inside the barrel is ejected along with the projectile, a conductive channel may form, which acts as a virtual antenna, and it can radiate the remaining energy as EM waves into the air. In this paper, we try to investigate the far-field EM radiation pattern and near-field electric field intensity after the projectile leaves the muzzle in four cases: case 1 is a bell-shaped plasma at $\omega _{\mathrm{ pe}} = 1$ MHz; case 2 is the same plasma at $\omega _{\mathrm{ pe}} = 100$ MHz; case 3 is a pillar-shaped plasma at $\omega _{\mathrm{ pe}} = 100$ MHz; and case 4 is the effect of a muzzle shunt resistor. The plasma is assumed to be about 5 m high, and is formed on top of the muzzle and behind the projectile, and a 1-kV voltage excitation source with frequencies ranging from 100 MHz to 1 GHz is located at the breech to excite the railgun and plasma combination. Three field probes located 10 m away from the projectile are set up to record the field intensities. We simulate the frequency response of this system with a finite-difference time-domain code. The results show that the plasma is not a very good radiator, and the field coming out of the muzzle is contained in a region near the muzzle because of the plasma. The EM radiation in the postfire period is not as strong as in the firing process.