High current performance of the 43 cm long Ranchero generator

A Ranchero flux compression generator (FCG) was recently tested at the 76 MA level. Ranchero generators were designed to be cost effective high current devices, and a variety of configurations have been tested. The Ranchero armature is a 152 mm diameter aluminum cylinder with a 6 mm thick wall. The high explosive (HE) is detonated simultaneously on axis, and the armature is expanded by a factor of two. At the final 300 mm diameter, the circumference is over 950 mm, which has been anticipated to accommodate currents approaching 100 MA. The test was performed with a 43 cm long module having an initial inductance of 56 nH, and a load inductance of 0.55 nH, consisting of a short load feed slot and probe grooves. A 12 mF capacitor bank at ~16.5 kV provided the initial 3.75 MA seed current. The performance of the generator with this load was calculated using a 2D MHD ALE code, and agreement was excellent. Generator design, test data, and details of the MHD calculations are given. The most important aspect of the results is verification of codes at the 76 MA level. The same codes do not show excessive losses up to the 100 MA level, and it is a much smaller extrapolation to that level at this time.