Magnetic Diffusion in Railguns: Measurements Using CMR-Based Sensors

Abstract

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 m) manganite films, which exhibits a colossal magnetoresistance (CMR) effect and has very small sensitive areas (e.g., 0 5 mm 50 m). 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.

Measurement of the Magnetic Field Distribution in Railguns Using CMR-B-Scalar Sensors

“…The comparison to experiments with steel and Dural rails (see Figs. 11 and 12 of [2]) shows that the highest B-field is concentrated at the edge of the copper rails. It agrees with theory that the diffusion time increases with increasing conductivity hindering the B-field to expand into the conductor [7].…”

“…A new generation of CMR-B-Scalar sensors, used for the experiments presented in this paper, has a very small volume and is therefore suitable to measure the B-field distribution close to the rails. An earlier paper [2] reported about the use * corresponding author; e-mail: oliver.liebfried@isl.eu of these sensors in measuring magnetic field diffusion in railgun equipped with different material. Different rail material influences the current distributions due to the interplay between conductivity and skin effect.…”

Single-Shot Performance of RAFIRA

“…First of all, the rails can be relatively easily mounted and removed. More importantly, the setup has proved to be very suitable for testing and developing diagnostic tools such as Doppler radar technology [6], current distribution measurements [7], or magnetic field sensors based on colossal magnetoresistance [8]. The type of projectile used during the experimental campaign is shown in a side view in Fig.…”

Diagnostics for Kinematics on MTF at NRL

“…Colossal magnetoresistance sensors are solid-state and very sensitive field detectors [2]. An array of such probes would give position-time data.…”