Observations on the limit velocity of plasma armatures [for railguns]

Free-plasma armatures leak plasma back into the bore. The plasma is subjected to the high rail-to-rail voltage behind the armature and conducts current. As velocity is increased the rail-to-rail voltage increases and these secondary currents increase. The flow of secondary current dramatically reduces the accelating force on the armature. At velocities of 5 to 6 km/s, the secondary currents reduce the acceleration to zero. Increasing the drive current or the barrel length has little effect on velocity. The two most promising methods of overcoming the problem are reduction of rail-to-rail voltage and elimination of the residual plasma in the breech region. Preliminary experiments on both approaches show considerable promise