Evaluation of Solid Armature\´s In-Bore Position, Velocity, and Current Distribution Using $B$ -Dot Probes in Railgun Experiments

In this paper, the measurement of the in-bore position and velocity of the armature is performed using B-dot probes. Nine B-dot probes are installed in the rail-to-rail insulator at different distances from the breech. Based on some simplifications of the current flowing in the armature, the magnetic flux formula of the probe is derived. It is found that when the armature passes by the probe, the ratio of magnetic flux of the probe and armature current reaches to its peak value. Thus, using the integrated B-dot probe signals and armature current, we can obtain the armature´s position as a function of time, and then the velocity can be obtained. Compared with zero-crossing method, this method considers the influence of di/dt to the signals of B-dot probe, and is more theoretically precise. The B-dot probe signals are also used to analyze the distribution of the armature current in launch process.