A TIME-DEPENDENT MODEL FOR RAILGUN PLASMA ARMATURES

In this paper a one-dimensional, time-dependent model is described for the analysis of railgun plasma armatures. The model assumes that the armature is isothermal, and that the electrical conductivity and degree of ionization in the plasma are uniform and constant in time. The model is applied to the analysis of three problems-armature initiation, armature response to a change in current, and armature response to a change in mass. In each case, the perturbation induces damped oscillations in the armature length and projectile acceleration about the corresponding steady-state values. The period of the oscillations is, for early times, approximately equal to 3leq/a0, where leq is the equilibrium armature length corresponding to the steady-state solution and a0 is the acoustic propagation velocity in the plasma. The exponential decay time for the cases studied ranges from 140 to 200μsec. Although most calculations are completely numerical, a partly analytic, limiting-case perturbation solution of the governing equations is also carried out. This analysis suggests why the same oscillation period is obtained in all three cases. The impact of transient phenomena on gun performanceand diagnostics, as well as plans for additional analyses, are discussed. © 1988 American Institute of Physics.