Study and implementation of a new rail geometry for a 10 MJ large caliber electromagnetic launcher

During the launch of a projectile with an electromagnetic accelerator, one of the most critical points to ensure the quality of the conversion of electromagnetic energy into kinetic energy is the sliding contact. In fact, given the order of magnitude of the velocities—around 2 km/s—and electric currents—around 2 MA—involved during a launch, the slightest failure of the electrical contact could cause significant mechanical and electrical damage to the railgun structure. Due to well-known phenomena such as the velocity skin effect and the proximity effect, the current density tends to concentrate at the edges of the rails instead of being distributed homogeneously over the entire rail section. In the case of flat rails, this tends to concentrate the current density and, consequently, the magnetic pressure in the corners of the rails, causing a deterioration in the quality of the sliding contact, which is all the more serious as the caliber increases. In fact, in the case of the NGL-60 60 mm caliber 6 m rail gun recently developed at the Franco-German Research Institute (ISL), which aims to fire larger projectiles, including embedded measurements, previous experiments have shown that flat rails are not entirely satisfactory at high speeds. The aim of this study is, therefore, to prove experimentally and numerically that a railgun structure with convex rails is a viable alternative at high current and high velocity levels, particularly for large calibers (above 40 mm). This geometry is tested on the NGL-60 railgun facility at energies up to 7 MJ: muzzle velocities in excess of 2.3 km/s are demonstrated and compared for flat and convex rail configurations and adapted projectiles. This experimental work is supported by FEM simulations to interpret the observed differences.