The Path to 100 MJ Ranchero Experiments

Ranchero is the name given to a class of Los Alamos coaxial flux compression generators (FCGs) that are detonated simultaneously along the cylindrical axis. An experiment was reported at MG-XIV in which a Ranchero FCG produced 76 MA peak current, and in MG-XV a design was presented which was intended to overcome a weakness uncovered in the 76 MA test. The name used for the new Ranchero configuration is “Ranchero-S”, and that improvement has now been successfully tested. The results of the test are presented in detail in another paper in this conference. This paper reports on scaling studies that are benchmarked by recent experiments, and which demonstrate the approach that would be taken to extend the Ranchero-S performance to levels of 100 MJ and 1.5 Weber. The primary scaling parameter for achieving larger currents is increasing the circumference of the FCG. Detonation systems are available in lengths of 0.43 m, 0.72 m, 1.0 m, and 1.44 m. The longer FCGs can operate with lower initial current for any given peak current and load, which allows them to be less effected by early time back pressure. However, at very high initial current, the effect of having a substantial field operating on a long armature over a substantial time can be seen. As diameter is increased, the flux compression time is increased if the initial inductance is held constant. The flux compression time can be held constant as radius is increased by keeping the armature to stator gap constant, with the result that the ideal gain is reduced for a given module length. The various possibilities are presented, with an emphasis on operating at current levels that approach the limits imposed by armature kinetic energy versus magnetic pressure. Another key feature in performing 100 MJ experiments is the existence of a booster generator which can produce seed currents well in excess of the three to four MA that can be delivered by the 2.4 MJ capacitor bank available at the Los Alamos explosive pulsed power firing facility. The MK-IX generator, which has been used in many experiments previously reported, has potential for producing the necessary seed current. However, a new booster FCG is being developed for that purpose, which will employ modern machining techniques to replace labor intensive methods required by the MK-IX fabrication. This FCG is called the MK-X, and the first test of this device is imminent. Either the MK-IX or the new MK-X booster will need further experimentation to demonstrate the capacity for delivering the approximately 2.5 Weber flux to a Ranchero FCG that projections in this paper require for the full 100 MJ, 1.5 Weber performance.