Electrically-launched mm-sized hypervelocity projectiles

Abstract

An electrothermal research gun capable of firing small cylindrical projectiles up to 4 km/s has been developed. While electromagnetic forces certainly exist in the system, it is not an electromagnetic launch system, but rather utilizes an electrical arc to produce a rapidly expanding gas that is used as the working fluid. A pointed copper anode is insulated such that the arc initiates only at the very tip, while the electrical circuit is completed through both the projectile and the barrel. Experiments show that copper vapor from the eroding copper electrode is the most likely working fluid of the gun, however, a portion of the aluminum projectile is also eroded. The design was directly aided by simulations performed using the multiphysics hydrocode ALEGRA developed by Sandia National Laboratories. Simulations included investigating the anode tip shape as well as limiting the expansion of the chamber due to the rapid expansion of gasses caused by the arc. Comparisons of projectile velocity profiles from Photon Doppler Velocimetry, barrel expansion, and pellet erosion with the ALEGRA results were utilized as benchmarks, leading to significant velocity gains for given energy inputs.