Arcing phenomena in transitioned solid armatures

In this study of arcing phenomena in transitioned solid armatures it is proposed that following forward acceleration of the arc plasma, re-strikes occur towards the rear of the contact surface resulting in commutation of current to the re-strike arcs. Thus a repetitive sequence of current conduction is predicted at a frequency dependent on the arc transit time along the armature surface. An analytical solution of the proposed theoretical model for the arcing phase evaluates the transient rail/armature gap voltages due to arc voltage, rail and armature resistances and magnetic flux changes. Comparison of the predicted rail/armature gap voltages at the front of the armature with measured muzzle voltage waveforms for a typical 90 mm armature shows sufficiently close agreement to support the validity of the theoretical model. The additional resistive losses as a result of transition are estimated to be >30% of the exit kinetic energy of 10 MJ. The deposition of most of this as thermal energy in the rail/armature gaps is expected to have a significant impact on structural design requirements