The EMET railgun projectile

The EMET projectile uses joule heating to accelerate the projectile in a railgun with a predominantly electrothermal driving force. The structure is designed to conduct armature current within a thin annular band around the shank of the large L/D dumbbell-shaped projectile. Current is initiated by a fuse located around the shank, and an impedance of 8 mΩ is achieved, compared to the 1-2 mΩ observed for electromagnetic (EM) guns. A supersonic nozzle in the projectile tail section expands and cools the armature plasma to raise its resistivity, prevent secondary arcs, and provide additional accelerating thrust. Experimental data are presented for 9.5 mm diameter, 5 gm projectiles, accelerated to nearly 600 m/s at 55 kA in a 0.9 m railgun. The armature remains confined in the projectile structure, and 75% of the acceleration is provided electrothermally. The calculated armature temperature is 3.0-3.5 eV, and significant rail burning is observed, consistent with the 5×10⁸ A/m current density of the contained armature. It is concluded from a current density argument that the EMET projectile is best suited to small-bore gun applications