| The goal of a plasma armature railgun is to accelerate the projectile to hypervelocities (i.e., to velocities beyond 5 km/s). Despite extensive research, projectile velocities achieved in the plasma armature railgun experiments were under 6-8 km/s--unfortunately, far less than predicted theoretical values. Experimental and numerical studies did not bring a full understanding of the factors limiting performance of the plasma railgun. The numerical studies so far have been limited to 1-D and 2-D computer models. In this dissertation, it is demonstrated that these models inadequately predict the main physical features of railgun plasma flow. To understand the railgun physics, 3-D magnetohydrodynamic (MHD) modelling is necessary.; To perform a 3-D MHD time-dependent computer simulation of the plasma armature railgun, a new code MAP3 (MHD Arc Plasma) was developed at University of Tennessee Space Institute (UTSI). MAP3 provides the first qualitative and quantitative understanding of 3-D physical phenomena in the plasma armature railgun. The results of the 3-D computer simulation for 1-cm and 2-cm bore railguns with ablating walls, are presented.; A profound influence of the inherently 3-D nature of the railgun electromagnetic field on the plasma flow is demonstrated. A strong spatial nonuniformity of the electromagnetic force generates a flow of plasma towards the projectile near the rail and away from the projectile along the center of the bore. This plasma flow is exactly the opposite to flow provided by the previous 2-D numerical models. A zone of high-shear flow near the rail surfaces can increase viscous losses, which are not accounted for in the usual performance estimates.; A satisfactory qualitative agreement was demonstrated between numerically obtained B-dot signal and typical experimental data. This process may play an important role in the formation of secondary arcs. MAP3 can be extended to analyze conditions believed to be accountable for the development of the secondary arcs and to provide reliable quantitative simulation. |
