Magnetic Diffusion in Railguns: Measurements Using CMR-Based Sensors

Magnetic diffusion is of great importance in the domain of electromechanical energy conversion since it can be a performance-limiting mechanism. This paper deals with magnetic diffusion in the case of the rails of a railgun. The experiments benefit from the use of a new type of high magnetic-field sensor based on thin ( < 1 mum) manganite films, which exhibits a colossal magnetoresistance (CMR) effect and has very small sensitive areas (e.g., 0.5 mm times 50 mum). Some basics about CMR and the design of the sensor are given. Several sensors were used and calibrated in the course of static transient railgun experiments. Here, varying spatial field distributions due to the use of different rail materials were recorded. Magnetic-field measurements during railgun operation with projectile velocities exceeding 1000 m/s have been successfully performed. By comparison with 3-D finite-element calculations, interesting results concerning magnetic diffusion have been worked out.