Impact of helix geometry on MCG flux losses [magneto cumulative generators]

Explosively driven magnetic flux compression has been the object of research for more than three decades. Recently heightened interest has been focused on the basic physical mechanisms that determine the performance of helical magneto cumulative generators (MCGs). Two single-pitch helical flux compression generators of different sizes have been tested using current-voltage probes and optical diagnostics. The main parameters used to characterize the experimental performance of the flux compression generators were the flux conservation and theoretical current gain of each type of generator. Helices with constant pitch and differing separation between wires as well as wires with different insulation thickness were tested and analyzed with respect to their flux conservation and theoretical current gain. Preliminary results show that the insulation thickness plays only a minor role for a change in flux conservation due to geometry in the range from 0.01 to 0.5 mm provided that no internal breakdown occurred. Additionally, the overall physical dimension of the generator was modified to allow for a substantial increase in initial inductance. The outer diameter of the generator armature was held constant at 1.5 inches and the coil diameter was varied from 2.6 to 3.5 inches (expansion ratio of 1.7 or 2.3, respectively). The results gained from the conservative expansion ratio of 1.7 were used as a base to compare to the generator performance at the more aggressive expansion ratio of 2.3. First results show that an expansion ratio of 2.3 produces viable results for a partially annealed Aluminum armature with a Gurney angle of approximately 15 degrees.

I. Introduction

Helical Magneto Cumulative Generators (MCGs) have been the subject of extensive study for nearly half a century. It is thought that these types of devices, while capable of amplifying energy significant amounts, have yet to maximize their potential performance due to intrinsic flux losses. While several theories exist as to the cause of the flux loss, insufficient studies on generic MCGs are available to be able to pinpoint its exact nature. The interest in the flux loss associated with and overall performance of helical MCGs prompted their study as part of a Multi University Research Initiative (MURI).