Abstract

A series of experiments and simulations were performed as proof of concept that an electrically powered research gun could propel small cylindrical projectiles to hypervelocities. Although small-caliber electrothermal accelerators and other electromagnetic launch systems have been utilized for some years for laboratory hypervelocity impact and other studies [1-5], we developed a simple, reproducible device that allows impact studies and direct comparison to magnetohydrodynamic (MHD) simulations for design considerations, efficiency improvements, and validation studies. This work focusses on 4.8 mm cylindrical 7075-T6 aluminum projectiles with a length to diameter ratio of one (nominally a mass of 0.24 grams) and a 150-mm long, 25-mm outer-diameter 4043 steel barrel with a 4.8-mm diameter bore and 9.5-mm chamber that acts as the electrical cathode. The anode consists of a 6.3-mm diameter copper rod that is reduced to 2.9 mm then tapered to a point with the tip length over diameter ratio (L/D) varying from 2 to 5. The tip is placed at the chamber/bore junction. The copper anode is insulated by a polyethylene sleeve and epoxy surrounding the electrode such that the arc initiates only at the very tip. A 191 μF capacitor was used as the power source for all experiments. The applied voltage was varied from 10 kV to 20 kV, and the resulting inductance of the system varied from approximately 320 nH to 450 nH (due to varying separation in the copper transmission lines). Fits to the current pulse using an LRC circuit resulted in resistance on the order of 10 mΩ to 15 mΩ. Typically the portion of the electrical pulse responsible for the bulk of the acceleration of the projectile occurs within the first 15 μs; however, the projectile is accelerated during the entirety of the time it remains in the barrel, which is on the order of 40 μs to 50 μs.

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