On the Results of an Experiment with a Megajoule Class Helical Flux Compression Generator Operating at Above Nominal Levels of Current and Voltage Stress

An experiment conducted with a megajoule class helical flux compression generator (HFCG), operating into a primarily inductive load, is described. The motivation behind the experiment was to benchmark the performance of the generator at higher currents and voltages than were tested in prior experiments. The intention was to push operation into a regime where flux loss was likely to become nonlinear, thereby gaining some insight into performance limitations of the design. Another goal was the desire to benchmark the suite of computational tools used to predict the performance of the design, especially in regimes of nonlinear flux loss. In the experiment, the HFCG was seeded with 105 kA (1.05 Wb), and produced 8.6 MA (0.28 Wb) into the load. This result differed significantly from computational models of the experiment, which predicted greater than 10 MA into the load. While more than one source of flux loss was observed in the waveforms, the dominant source of loss appears to be associated with joule heating and magnetic diffusion, which were found to have the most impact during the latter stages of HFCG operation. Details of the experiment design, setup and execution will be given. Analysis of the captured data, along with comparison of these data with model predictions and past experimental data, will be shown.

I. Introduction

In early 2010, Lawrence Livermore National Laboratory (LLNL) conducted the first of many experiments with the “Mini-G” or “MG” explosive flux compression generator (FCG) system. The MG platform was designed to produce upwards of 60 MA and 8 MJ into an inductive load [1]. The MG platform is composed of two FCG stages - one helical FCG stage which feeds a coaxial FCG. The helical FCG, which is the focus of this paper, is used to boost the output of a capacitor bank in order to seed the coaxial FCG with 8 MA of current, or roughly 1 MJ. An overview of the helical FCG design has been given previously in [1].