Velocity-induced current profiles inside the rails of an electric launcher

Previous investigations showed that an array of novel CMR-B-scalar sensors based on the Colossal Magnetoresistance effect can be used to measure the magnetic field distribution in the vicinity of the rails of a railgun. However, the data obtained suffered from electromagnetic interference. Therefore, the measurement system was considerably improved with respect to the signal quality. In this publication the results obtained during the dynamic operation of the ISL railgun RAFIRA are presented. The magnetic field distribution in the vicinity of the rails was measured at different armature velocities. Additional information was obtained using high-speed camera snapshots. The experimental results are compared with simulations performed with the finite element code COMSOL Multiphysics. In particular, the influence of the armature current on the measurements is discussed. It is concluded that the magnetic field distribution in the vicinity of the rails clearly indicates an increased current concentration in the rear part of the armature-rail contact interface. Moreover, the current concentration depends on the speed of the armature. Velocity-dependent skin depths at the surface of aluminum (Dural) rails for projectile velocities ranging between 750 m/s and 1500 m/s are given.