Experiments with Multi-Megampere Explosively Formed Fuses in Cylindrical Geometry

摘要

Taking advantage of the high energy density attainable in the magnetic field of an inductor requires a prime power source capable of producing very large currents and a means of extracting the energy as a fast current pulse from the inductive store. Many existing high current sources have pulse risetimes of hundreds of microseconds, while most pulsed power applications have submicrosecond pulse requirements. In principle, high current opening switches represent a good solution to the problem. An inductor is charged over a long period of time by a relatively slow current supply with a closed switch completing the circuit. At a desired time, the switch is opened and the voltage produced transfers current rapidly to a load circuit. In practice, building opening switches that will carry multimegampere currents for hundreds of microseconds and then open on a submicrosecond time scale has posed an extremely difficult problem. Explosive-driven opening switches have been used in long-pulse applications for some time, but until recently the explosives systems used to drive these devices would not produce a rapidly opening switch. We have developed a fast technique for interrupting large currents by using explosives to extrude short sections of relatively thick conductors into long thin fuse-like conductors. Although the formation of the fuse requires about 2 mu s, the switch will sustain considerable voltage as its resistance rises, and it is feasible to deliver pulses with approx. 1 mu s risetimes to low inductance loads. We discuss here the small scale proof of principle experiments and 2-D hydrodynamics calculations that have led to an optimized cylindrical opening switch design. In addition, we will describe the results of testing a cylindrical switch at currents up to 4.6 MA, and give extrapolations for device designs for the 15 to 20 megampere range. (ERA citation 11:048232)