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Experimental Results on a 7-m-Long Plasma-Driven Electromagnetic Launcher

The Institute for Advanced Technology (IAT) at The University of Texas at Austin has been conducting research aimed at achieving muzzle velocities in excess of 7 km/s using a plasma-driven electromagnetic launcher. Plasma-driven railguns are susceptible to bore effects that limit muzzle speeds to about 6 km/s. The velocity ceiling is believed to be the result of the viscous drag of material ablated from the bore of the launcher. Ablation of bore materials, especially the insulators, is caused by the intense heat radiated by plasma armatures, especially at low speeds. The experiments reported in this paper are focused on overcoming the velocity ceiling of 6 km/s. A proof-of-principle experiment has been designed to launch 5-10 g polycarbonate projectiles to muzzle velocities in excess of 7 km/s with modest acceleration loads of 500 kG. Our approach to controlling bore ablation involves the following elements: (1) using magnetic augmentation to reduce power dissipation in the plasma; (2) using high-purity alumina insulators to raise the ablation resistance of the bore; (3) using pre-acceleration to prevent ablation of the bore materials at low velocity; and (4) using a synchronously driven distributed power supply to electrically isolate stages. This paper describes the consequences of excessive bore ablation, the rationale for the IAT experiment, and the results obtained during testing in 2009.