A Cross-correlation-based Method For Determining The Position And Velocity Of A Railgun Plasma Armature From B-dot Probe Signals

Abstract

In this paper we present a method for determining the position and velocity of a plasma armature from B-dot probe signals. This method utilizes the physical processes governing the plasma armature current density to model the leading edge of the armature as a unit step function since it has been shown that the current in a railgun plasma armature peaks near the base of the projectile. This model of the current profile is convolved with a previously derived impulse response function for the B-dot probe to give the probe unit step response which is a function of the velocity and the time of passage of the leading edge of the armature. The unit step response of the probe is compared with B-dot probe data via a local-area cross-correlation (LACC) coefficient. Two-parameter iteration determines the time of passage and the velocity of the leading edge of the armature as the values for which the correlation is maximized. This method has been successfully applied to both numerically simulated data and actual B-dot data from railgun firings. Results obtained using this technique indicate that significant improvement in accuracy for time of passage estimates can be obtained over previous ad hoc methods. Velocity estimates from individual B-dot probe signals can also be obtained.