Application Of Optical-Fiber Pins To Explosive, Pulse-Power Generators

Arrays of optical-fiber pins, known as microballoon optical pins, have been used to diagnose the dynamic deformation of an explosive pulsed-power generator. The pin data determine the effects of multimegampere electrical current loading on generator performance. The pins are required to work in the adverse environment of the generator, consisting of explosives and explosive products and very large, rapidly-changing electrical currents that give rise to intense electromagnetic interference. The optical pin is a shock arrival-time sensor consisting of an optical fiber tipped with a gas-filled microballoon about 200 microns in diameter. When a strong pressure pulse impinges on the microballoon, the shock-heated gas within the spherical shell emits a bright flash. The light is transmitted via the optical fiber to an electronic streak camera which simultaneously records signals from many pins. The signals from an array of these sensors measure the time profile of the impact of the explosive-driven armature with the stationary conical stator. Details of the microballoon pin are described at this meeting by Benjamin and Mayer. The microballoon pin was compared with the conventional flash-gap technique in which air, confined in a much larger space, is shock-heated to produce a time-of-arrival flash. The two methods gave essentially identical results on the first shot. Since the microballoon was more convenient to use and indicated a greater range of usefulness in future applications, we used it exclusively on the subsequent shots. The microballoon optical-fiber pin gave us the data necessary for the next generator design iteration and will be used extensively in the future.