Spatial characteristics of the EML plasma armature and the dependence on plasma composition

A simplified picture of a radiation-dominated plasma armature of an electromagnetic launcher (EML) is developed to evaluate in quasi-steady-state its spatial characteristics and their dependence on plasma composition, applied electric and magnetic fields, and possible temporal changes. A graphical solution of the energy balance equation is found which permits quick visualization of the effects of changing rail voltage or bore diameter. It is found that metallic vapor armatures will have plasmas extending to the highest expected pressures near the projectile. However, armatures consisting of the ablation products of G-9 or Lexan insulators or other nonmetallic plasmas such as hydrogen or argon cannot satisfy the energy balance conditions at high pressures unless the electric field is sufficiently high. Such armatures may not develop the desired magnetic pressure gradient in their leading edge to accelerate the projectile, with possible performance degradation. At low pressures (1-10 atm) in the trailing edge of the armature, the electrical conductivity can be significantly reduced by the high transverse magnetic field. It is concluded that this extended tail of low temperature plasma could be of importance in restrike phenomena