Experimental Ballistic Improvement in a Pure Electrothermal (ET) 25-mm Gun

The Soreq Propulsion Physics Division has recently initiated the development of a small-caliber pure electrothermal (ET) weapon. This paper reports the promising results obtained with a 25-mm ET gun. The currently mature gun technology based on conventional ballistic process is mostly limited because: 1) the propellant burning features dictate a curve that is entirely determined by the grain geometry and cannot be changed "online" and 2) the pressure gradient between the breech and the projectile\´s base strongly depends on the molecular weight of the combustion gases, which is almost propellant formulation independent. Removing the first limitation and reducing the second one is the key of the ET technology. ET guns use electric energy as the unique source of propelling energy. It is converted into a high-temperature plasma which interacts in the chamber with an inert cooling fluid that serves also as a propelling working fluid. In this study, two types of working fluids were tested: polyethylene and water. Polyethylene was found unsuitable for our purposes. Experiments, supported by simulations, show that the degree of water dissociation was enough to produce the required working fluid. Using 750 kJ of ET energy, 20% improvement in kinetic energy was obtained with a standard projectile without exceeding the maximum authorized breech pressure. It has been shown that the well-known barrel erosion issue is mostly due to the aggressive abrasion of the cartridge metal by the hot plasma jet. A new cartridge concept has been especially designed to overcome this problem. Results are very satisfactory