7.1.1 Historical Overview

The use of a fuse as an opening switch was first reported in scientific literature in the late 1950s and early 1960s. They were used in conjunction with controlled nuclear fusion experiments, fast pinches, or hypervelocity guns. These types of experiments require a typical current rise of the order of 10 ¹³ A/sec. Conventional practice had been to use high voltage capacitors in series with a closing gap (spark gap). However, it should be emphasized that we can only achieve a limited rate of current rise with this standard approach.

Starting with the basic voltage-current relationship for inductors

(7.1)

and assuming ideal conditions where the capacitor is the sole provider of inductance, also assuming modern high voltage capacitors with a typical self-inductance in the order of > 10 ^-8 H, the maximum dI/dt is limited to < 10 ¹² A/sec for a peak voltage of 100 kV. In order to increase peak current rise times H. C. Early and F. J. Martin devised a system that makes use of a "fast opening fuse" in a pulse shaping system to deliver a large dI/dt to a load. The fuse consisted of a copper foil sandwiched between copper terminals, arranged in a parallel plate transmission line setup. Fiber glass cloth was used as a quenching medium and thin Mylar sheets as additional insulators. With this inductive energy storage system with fuse opening...