Previous investigations have shown that an array of novel CMR-B-scalar sensors based on the colossal magnetoresistance effect can be used to measure the magnetic field distribution in the vicinity of the rails of a railgun. However, the data obtained suffered from electromagnetic interference. Therefore, the measurement system was considerably improved to obtain better signal quality. In this paper, the results obtained during the dynamic operation of the ISL railgun RAFIRA are presented. The magnetic field distribution in the vicinity of the rails was measured at different armature velocities. Additional information was obtained using high-speed camera snapshots. The experimental results are compared with simulations performed with the finite element code COMSOL Multiphysics. In particular, the influence of the armature current on the measurements is discussed. It is concluded that the magnetic field distribution in the vicinity of the rails clearly indicates an increased current concentration in the rear part of the armature-rail contact interface. Moreover, the current concentration depends on the speed of the armature. Velocity-dependent skin depths at the surface of aluminum (Dural) rails for projectile velocities ranging between 750 and 1500 m/s are investigated.

The bore of a railgun is a harsh environment with high transient magnetic fields, temperature gradients, and forces. Most common payloads in railgun launch are made from conductive materials. In this article, we consider the effects of the transient magnetic field on a conducting payload during an electromagnetic launch by a serial augmented hexagonal railgun. The magnetic field distribution in the proximity of a solid aluminum payload was investigated by numerical calculations and experimentally by using a CMR-B-scalar sensor array.

Railguns can reach higher muzzle velocities and fire rates than conventional guns. Muzzle velocities up to 2400 m/s and fire rates of more than 50 Hz have already been demonstrated with projectiles having a mass of 140 g and a square caliber of 25 mm. We investigated if a close-in weapon system (CIWS) based on a railgun performs better against incoming antiship missiles than a conventional CIWS such as the goalkeeper and propose solutions to optimize the performance of such a railgun. CIWSs are operational systems that defend a ship against incoming subsonic antiship missiles. However, the future antiship missiles will be supersonic and more difficult to defeat with conventional gun systems. Railguns are expected to perform better against these future threats thanks to their higher muzzle velocity and fire rate. Furthermore, the muzzle velocity within a single burst can be varied easily from shot to shot, generating a so-called intelligent burst. It allows varying the velocity of each projectile such that all projectiles arrive on the target at the same time. The number of projectiles, and thus the electrical energy required to achieve a target kill with an intelligent burst is expected to be lower than for railguns firing at constant muzzle velocity. In the first part, the performance of an electromagnetic CIWS is discussed using simulation models calculating the hit probability of a burst of projectiles fired with muzzle velocities ranging from 1200 to 2400 m/s and fire rates ranging from 75 to 300 rounds/s. The geometry of the target is that of a typical antiship missile, its velocity ranges from subsonic (300 m/s) to supersonic (600 m/s). The influence of the projectile mass on the performance of the system and the required electric energy was also investigated. We confirmed that the concept of intelligent burst reduces the required electric energy, especially against supersonic targets. The second part deals with some technical aspects of high fire rate railguns. We have shown experimentally that an automatic loading system allows increasing the fire rate of a medium caliber railgun from 50 to 75 Hz.

The use of brush armatures for accelerating railgun projectiles allows muzzle velocities in excess of 2.5 km/s and contact transition velocities of at least 1.8 km/s in middle-caliber launchers to be obtained. The technology developed at ISL is based on the use of multiple brush armatures. Asymmetric wear has been observed in dynamic launch experiments when the brushes were separated in shot direction. This indicates the presence of asymmetric current distribution. In this paper, mechanisms determining the current distribution of multiple brush armatures are investigated using a static approach. Experiments were performed using a section of the ISL EMA3 railgun with 270-mm-long rails. It had a caliber of 15 mm x 30 mm and was connected to a 150-kJ capacitor bank. Three series of experiments focusing on specific parameter variations are presented. The current distributions were recorded using small Rogowski coils placed around the brushes. Magnetoresistive sensors were used for highly local measurements of magnetic fields in the vicinity of the brushes. Results reveal insight into the contact behavior of multiple brush armatures. More specifically, phase transitions at the brush-rail interfaces can be observed. This is typical in dynamic experiments when the current commutates from one brush to another. The experiments are discussed with the help of PSPICE simulations.

A new single-axis gas thermal gyroscope without proof mass is presented in this paper. The device was designed, manufactured and experimentally characterized. The obtained results were compared to numerical simulation. The working principle of the gyroscope is based on the deflection of a laminar gas flow caused by the Coriolis effect. A bidirectional hot air flow is generated by alternating activation of two suspended resistive micro-heaters. The heated gas is encapsulated in a semi-open cavity and the gas expands primarily inside the cavity. The thermal expansion gyroscope has a simple structure. Indeed, the device is composed of a micromachined cavity on which three bridges are suspended. The central bridge is electrically separated into two segments enabling to set up two heaters which may be supplied independently from each other. The two other bridges, placed symmetrically on each side of the central bridge, are equipped with temperature detectors which measure variations in gas temperature. The differential temperature depends on the rotational velocity applied to the system. Various parameters such as the heating duty cycle, the type of the gas and the power injected into the heaters have been studied to define the optimal working conditions required to obtain the highest level of sensitivity over a measurement range of around 1000°/s. The robustness of the device has also been tested and validated for a shock resistance of 10,000 g for a duration of 400 µs.

The rapid fire railgun (RAFIRA), a unique railgun that can be operated in multishot mode, is well suited for the study of the influence of different rail materials on velocity and electrical contact of the armature and/or the wear of different rail materials. That is why we performed experiments with RAFIRA operated in multishot mode (firing rate of 50 Hz), using different rail materials (CuCr and Dural) and various shot energies. For these experiments, the shot energy for RAFIRA was raised, for the first time, up to the maximum energy at a disposal of 1.45 MJ per shot with projectile masses of over 120 g. In this way, we were able to show that the influence of the rail material depends on the applied shot energy: for low shot energies (<;1 MJ), CuCr rails show better results in terms of velocities and exit times of the projectiles. This effect vanishes for high shot energies (> 1 MJ). Whereas in terms of electrical contact, Dural rails show both less erosion and the capability to maintain a solid sliding contact until shot out for all energies applied.