Experimental investigations of plasma armatures in railgun launchers

Summary form only given. The behavior of the plasma armature, especially during the formation of secondaries, is an important issue in electromagnetic launchers. The structure of the plasma armature is being investigated using a compact B-dot array (separation distance=bore diameter), along with other diagnostics. Ablated material entering the plasma armature can lead to mass accretion, armature lengthening, formation of multiple secondaries through bifurcation or restrike, and other processes that degrade launcher performance. A code has been developed that deconvolves the signals from the B-dot array to yield the spatial and time dependence of the plasma armature. The technique is being used to study the effect insulator ablation has on the structure of the plasma armature. A novel metallic insulator has been designed to reduce the amount of ablation from the insulator surface. Metals have a much higher ablation threshold than the commonly used insulator materials such as G9 and G10. The metallic insulator being investigated is composed of layers of metal separated by thin layers of insulator material. Preliminary tests of composite insulators using copper and stainless steel have shown a decrease in the formation of secondaries and an increase in armature velocity for free are studies. The behavior of plasma armatures during launch of solid projectiles is also being investigated.