Efficiency, performance limits and scaling of rail launchers

The fundamental parameters that influence the performance and efficiency of rail launchers are shown to be: mechanical energy/bore volume (p₀), effective magnetic flux density (B₀) and the total mass/effective bore area (m). To achieve a high electrical efficiency these parameters should be minimized by increasing the bore diameter and reducing the bore length, subject to other design constraints such as increasing launch package mass. The efficiency of rail launchers is limited by energy losses in the rail and armature, arcing losses following transition and the barrel residual magnetic energy at exit. These are derived analytically including the effect of field diffusion, velocity skin-effect (VSE), predicted transition velocities and arcing phenomena. A range of aluminium alloy armatures with breech-fed copper rails are considered with kinetic energies up to 20 MJ and bore diameters from 40 to 180 mm. Electrical efficiencies for 10 and 20 MJ kinetic energy launchers with minimum diameters are estimated to be 52 and 62% respectively. An increase in efficiency to 67% is predicted for larger diameter launchers with transition velocities increased to >2.0 km/s due to lower energy density and electrical action