An insulator-metallic phase transition cascade for improved electromagnetic flux-compression in /spl theta/-pinch geometry

During an initial phase of an ongoing research program at Loughborough University, ultrahigh magnetic fields of up to 300 T (3 MG) have been generated. These have been produced using only 63 kJ from a fast capacitor bank to implode an aluminum liner in a /spl theta/-pinch geometry, and 14.7 kJ from a slow capacitor bank to provide an initial magnetic field. The paper analyzes various ways of improving both the /spl theta/-pinch magnetic flux-compression efficiency and its reproducibility. As a practical illustration, experimental evidence is presented to demonstrate the benefits obtained from the use of an insulator-metallic phase transition cascade made from powder aluminum.

I. Introduction

The FIRST experimental and theoretical investigations of electromagnetically driven magnetic flux-compression (commonly abbreviated as electromagnetic flux-compression) were related to the early nuclear fusion programs of the late 1950s and early 1960s [1], [2]. By analogy with plasma experimentation, both -pinch and -pinch geometries may be used, and many research programs using the later technique have electromagnetically accelerated a hollow metallic cylinder (a liner) to compress a hot plasma target (see [3] and the references therein). Driving a liner in geometry requires however a specialized power source having a very low impedance, which has led to many research groups undertaking their investigations in geometry [4]–[5] [9]. It was not until 1966 that successful electromagnetically driven magnetic flux-compression experiments reported by Sandia National Laboratories (SNL) [10] established that very high magnetic flux densities can be produced inside a thin liner, both with and even without the injection of any initial field (the Cnare effect). Results subsequently presented from similar investigations by the other research groups [11]– [13] were all, however, obtained without an initial field. Fig. 1. Electromagnetic flux-compression arrangement with initial field injected cumulatively. Direction of liner current corresponds to the first phase of compression.