Plasma armatures in large bore launchers

Summary form only given, as follows. Almost all experimental observations of plasma armatures in railguns have been made in bores less than 20 mm in diameter. A serious velocity-limiting interaction with the bore walls has been identified. The plasma radiates to the bore walls at power levels of several GW/m/sup 2/. The bore walls ablate and the ablated material enters the armature, resulting in an apparent drag. The author examined the ablation-induced drag as bore size is increased. Using a three-dimensional computational model, he determined plasma temperature and pressure distributions. Bore wall ablation and drag were then computed. It was found that plasma armature length and resistance increase only slowly with bore size. Radiant power densities do not change significantly, and the deleterious effects of ablation-induced drag decrease.<>