Evaluating the residual inductance of a Ranchero coaxial flux-compression generator as storage inductance for powering imploding hydrodynamic liner loads

The Ranchero coaxial flux-compression generator system is an explosive-driven generator designed for high current (up to 100 MA per module) applications. A single module consists of a 15.2 cm diameter armature that is detonated simultaneously along its axis, to expand a factor of two out to the coaxial stator. Most, but not all, tests have used a taper on the stator to minimize flux trapping as the armature closes the generator volume. The authors have experimentally evaluated the residual inductance for a variety of stator insulation thicknesses, and reported some of these results in previous work. For a 1.4 m-long module, the residual inductance is ∼3.6 nH using 0.5 mm thick polyethylene insulation along the stator. Thicker insulation increases the residual inductance. Since some of that residual inductance is due to flux that has diffused into the generator conductors, not all of it can be considered storage inductance for driving short time scale experiments. In addition, the armature is shocked by the explosive, extruded to half its original thickness, then shocked on impact with the stator, all while carrying a large current. These factors lead to increased diffusion, further reducing the amount of flux available for microsecond time scale experiments. Experimental data and MHD calculations are compared to evaluate the usefulness of flux in the residual inductance for transfer to loads of interest