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This paper presents experimental solutions developed recently at the French-German Research Institute of Saint-Louis (ISL) railgun facility EMA3 (muzzle velocity [v.sub.o] < 1900 m/s, applied energy per shot [E.sub.prim] < 0.9 MJ, l = 3 m, cal. = 15 x 30 [mm.sup.2]). New quasi-segmented rail configurations: one advantage of multiple brush armatures is the possibility of developing new armature-rail configurations, which vary the width of the rail as a function of the rail length in order to maximize the multiple brush armature performance. Improved Doppler radar measurements of the projectile dynamics in the launcher: the overall performance of a Doppler system might be limited by the decrease of the signal-to-noise ratio due to the formation of plasma arcs during the shot. A new approach, circumventing this problem, is presented. Parasitic mass is considered as a key problem of railgun technology in general, and of the use of brush armatures in particular. A new idea using the force behavior of multiple brush armatures is presented. Whereas X-ray flash radiographs provide useful information about the force distribution between multiple brushes, the measurement of the current distribution is more difficult. A method to measure the latter by benefiting from the discontinuity of the armatures is presented. Index Terms--Armatures, Doppler radar, metrology, railgun.

A precise and continuous measurement of the velocity of projectiles inside the barrel would permit to improve the understunding of the dynamic behavior of railguns. Friction-related questions, the mechanical stability of projectiles, or mass loss of armatures are problems to be mentioned in this context. One possibility to monitor the projectile dynamics is the use of a conventional Doppler-radar. In this paper, the experimental setup of a W-band Doppler system and its application at railgun experiments are described. First results obtained using a 15 x 30 [mm.sup.2] rectangular caliber railgun are presented. The maximum muzzle velocity for the series of experiments is about 1300 m/s. Depending on the quality of the electrical contact between rails and armatures, a very good agreement between the projectile dynamics measured by the Doppler-radar and the information given by several B-dot signals recorded at several positions along the barrel is obtained. If no electrical arcs are formed during the shot, the projectile is properly detected until it reaches the muzzle of the launcher (l = 3 m). Some aspects of friction are discussed to illustrate the evaluation of the data obtained. Index Terms--Armature, Doppler-radar, railgun.

The use of metal fiber brush armatures incorporated in sabots made of insulating low-density materials in distributed energy storage (DES) railguns requires the avoidance of permanent high-current plasma arcs (contact transition). The resulting plasma might damage the sabot and may also lead to the malfunction of the DES system. In order to determine critical parameters concerning the transition of brush armatures, a series of experiments was performed using the ISL-EMA3 railgun (DES, 3 m, 15 x 30 [mm.sup.2], 620 kJ). The maximum muzzle velocity obtained during these experiments was about 1200 m/s. A qualitative model of brush-rail contact, assuming that contact transition is mainly due to mass loss of brushes, is presented. The mechanisms causing mass loss were investigated. It could be shown that joule heating is primarily limiting brush armature performance, while friction is not negligible. Index Terms--Armature, contact transition, railgun.

Using miniaturized Rogowski coils developed at ISL, we are able to measure the currents flowing through moving metallic fiber-armatures in a railgun. The 15 mm square bore railgun is 0.5 m in length and is powered by a 150 kJ capacitor bank. The peak current is about 200 kA and typical launch velocities with this test bed reach 600 m/s. The armature consists of two fiber brushes made of the same metal (e.g. Cu-Cd) or two different metals (e.g. brass and Cu-Cd). The current distribution between the two brushes has been measured during the shot. A special voltage probe placed on one rail provides information about the rail resistance variation during projectile passage. A comparison between the experimental results and the current distribution calculated with a three dimensional finite element code, taking into account thermal effects, is presented.

We have attempted the improvement of several different measuring methods used in railguns. These technics cover several topics like measurement of main current, voltages on switches and inductors and magnetic field distribution with B-dot probes. A Rogowski coil coupled to a new type of electronic circuit (called 'switching gain circuit') allows an accurate measurement of resistance as low as a few m[ohms] in a pulsed power facility. Low voltage measurement in a high voltage circuit (100 V in comparison to 10 kV) have been made on semi-conductors and switching components in pulse power system. Special circuits rejecting the high voltage have been developed. Finally, we describe the measurements of the current distribution along a metallic projectile moving in a railgun by mean of previously calibrated B-dots.

In the following work, sacrificial claddings filled with different brittle materials were investigated, from concrete foam to granular media. They were subjected to blast loading using an explosive driven shock tube, while a sensor measures the load transmission and a high speed camera records the compression of the core. From a macroscopic point of view, concrete foam and granular media can act efficiently as a crushable core but differs greatly in terms of energy dissipation mechanisms. To compare them, granular media was at first treated as a cellular material, and different key parameters (plateau stress, densification strain) were computed using the energy absorption efficiency methodology. The presented tests results, coupled with observation in literature, allow a better understanding on the crushing process of a granular media. In particular, granular media tend to work as a core even for low intensity load, contrary to more classical crushable core.