Modeling of a Small Helical Magnetic Flux-Compression Generator

In order to gain experience in explosive pulsed power and to provide experimental data as the basis for computer modeling, a small high-explosive-driven helical magnetic flux-compression generator (FCG) was designed at the Swedish Defence Research Agency. The generator, of which three have been built, has an overall length of 300 mm and a diameter of 70 mm. It could serve as the energy source in a pulse-forming network to generate high-power pulses for various loads. This paper presents a simulation model of this helical FCG. The model, which was implemented in Matlab-Simulink, uses analytical expressions for the generator inductance. The model of resistive losses takes into account the heating of the conductors and the diffusion of the magnetic field into the conductors. The simulation results are compared with experimental data from two experiments with identical generators but with different seed currents, influencing the resistive losses. The model is used to analyze the performance of the generator.

I. Introduction

Small helical magnetic flux-compression generators (FCGs) are attractive energy sources for compact pulsed-power systems [1], [2]. A helical FCG usually consists of a conducting cylindrical coil (stator) and a conducting cylindrical tube (armature) filled with high explosives. The stator and armature are, in most cases, connected via an inductive load into which the magnetic flux is to be concentrated. The stator is magnetized by a seed current with a return path via the load and armature. When initiated, the explosives in the armature will rapidly expand the armature in a conical fashion. When the armature contacts the crowbar (here, it is a time which will be referred to as the crowbar time), it will short out the seed current and trap the magnetic flux in the shrinking volume between the stator and the armature. As the detonation moves forward, the stator coil is shorted out turn by turn by the armature, reducing the inductance of the circuit. If the flux is conserved, the current in the circuit will increase and can be used for various applications. Of special interest is using an FCG together with a pulse-forming network to provide a high-voltage pulse for the generation of high-power microwaves [3].