Highly local measurements of strong transient magnetic fields during railgun experiments using CMR-based sensors

The accurate measurement of the magnetic field distribution during electromagnetic launch experiments is an ambitious task. Loop sensors are widely used for detecting the change in magnetic flux. However, this technique is mostly used only for qualitative purposes, e.g., for triggering various devices. This paper deals with the use of another type of high magnetic field sensor based on thin (< 1 mu m) manganite films, which exhibit the colossal magnetoresistance (CMR) effect. This sensor measures the magnitude of the magnetic induction and can have very small sensitive areas (e.g., 0.5 mm x 50 mu m). Some basics about CMR and the design of the sensor are given. Several sensors were used in experiments performed with the ISL-launcher EMA3 (E-Prim = 0.6 MJ, t = 3 m, cal = 15 mm x 30 mm). Transient magnetic field profiles with rise times of approximately 50 mu s and amplitudes up to 4 T were recorded. The results obtained with the CMR sensors are compared with those of conventional loop sensors. Also, some metrological peculiarities due to high-frequency coupling to the detector circuit are mentioned. The highly local measurements of these CMR sensors were validated by results obtained from 3-D finite element (FE) calculations of the magnetic field distributions.