370 IEEE TRANSACTIONS ON MAGNETICS, VOL. 43, NO. 1, JANUARY 2007 Highly Local Measurements of Strong Transient Magnetic Fields During Railgun Experiments Using CMR-Based Sensors M. Schneider , R. Schneider , V. Stankevi˘ c , S. Balevi˘ cius , and N. ˘ Zurauskien˙ e French-German Research Institute ISL, Saint Louis F-68301, France Semiconductor Physics Institute, Vilnius Gediminas Technical University, Vilnius LT-01108, Lithuania 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 ( 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 50 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 ( MJ, m, mm 30 mm). Transient magnetic field profiles with rise times of approximately 50 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. Index Terms—Magnetoresistance, railguns, sensors, skin effect. I. INTRODUCTION T HE ACCURATE measurement of high transient magnetic fields during electromagnetic launch experiments is both ambitious and necessary. It is ambitious because the experi- mental conditions during these kinds of experiments are such that sophisticated metrological systems can easily be disturbed or even damaged. It is necessary, because existing codes are not yet capable of modeling corresponding transient “multiphysics” problems. Therefore, accurate measurements might improve the development of appropriate simulation tools. The velocity–skin effect is seen as being one of the major problems in railguns [1], [2]. The question, if and how far this effect is responsible for the limited performance of solid arma- tures is still the subject of research [3], [4]. The main goal of this preliminary study is to accurately measure the spatial dis- tribution of the magnetic field close to the rails after a projectile passes. A new kind of magnetic field sensor, the working prin- ciple of which was only discovered a decade ago and which can have very small measurement volumes, is seen as a promising tool in this context. II. EXPERIMENTAL SETUP The experiments were performed using the EMA3, an ISL-railgun (Figs. 1–2), whose main parameters are listed Digital Object Identifier 10.1109/TMAG.2006.887706 Fig. 1. The projectile consists of a GRP-sabot and 6 Cu–Cd brushes, the arrow indicates shot direction. in Table I. During the study presented in this paper, the EMA3 was equipped with rectangular rails with a caliber of 15 mm 30 mm and a length of 3 m. Two entirely different kinds of experiments were conducted using the colossal magne- toresistance (CMR) sensors (in this study, only sensors based on LSMO films were used, for explanation see Section III): static and dynamic experiments. Static experiments were carried out by short-circuiting the railgun at the muzzle. The sensors were placed at five different positions, P1–P5, near to the rails as sketched in Fig. 3 and a current pulse with a maximum of around 200 kA was delivered to the closed cir- cuit. The time-dependent profile of the magnetic induction was recorded. Note that the loop sensor, also shown in Fig. 3, was mounted at the same height as position P3, but only with 1-mm distance from the rails. 0018-9464/$20.00 © 2006 IEEE