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Published: 2010

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In the late 1990s, Los Alamos pursued a coaxial flux compression generator (FCG) concept that was described in several publications under the name 'Ranchero.' These FCGs were designed to be cost effective high current generators, and a variety of configurations were 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 as the armature expands a factor of two, the wall thins to H" mm. At the final 300 mm diameter, the circumference is over 900 mm, and this should allow currents to be generated in the 90 MA range. No tests significantly over 50 MA have been performed but an experiment is planned. We have recently begun using Ranchero devices for a new application and we continue to improve the design. In this paper we describe recent tests of Ranchero and its subsystems. The load for our new application is an imploding aluminum liner that would deform due to the magnetic pressure applied during the initial flux loading. It will, however, implode properly when powered only during the H"9?s Ranchero flux compression time. This gives rise to a new system with explOSively formed fuse (EFF) opening switches and an integral closing switch that isolates the load. A capacitor bank delivers 2.8 MA to the Ranchero circuit in H"5?s. During this time, four parallel 63.5 mm wide EFFs, external to the coaxial system, complete the circuit. After armature motion begins, insulation which initially isolates the load is severed, connecting the load to the FCG in parallel with the EFFs. External HE charges are initiated on each of the EFFs to produce a resistance rise timed to not precede closure of the load isolation switch. The EFFs achieve significant resistance, and the flux remaining in the 191 nH generator and 3 nH transmission line is compressed to generate 30.85 MA in a H"2.5 nH static load. On three tests, the EFF system has operated flawlessly, and only H"00kA is driven back into the EFFs during peak voltage of the generator output. A test incorporating a 19.5 nH dual liner dynamic load has also been completed, and these results are also presented. Ranchero generators have been operated with armatures from 43 cm to 1.4 m long, corresponding to initial inductances from 56 to 191 nH. MHD code modeling gives better agreement with experiments using modules 43 cm long than the 1.4 m modules, and these results will also be presented.