Examination of Initial Strike and Restrike Modes in Exploding Metallized Films

Abstract

The discharge modes of a capacitive exploding metallized film setup are discerned. Long exposure still images of the plasma formation during the initial strike and restrike are presented.Index Terms-Aluminum metallized film, exploding film, plasma imaging, pulsed power. E LECTRICAL exploding films have been used in a wide variety of applications, including fast opening switches, ceramic joining, and production of nanopowders and initiators. An exploding conductor event is separated into two distinct regions. The initial strike is typified by Joule heating of the conductor to a superheated liquid state. If there is sufficient energy remaining after the initial strike, a restrike occurs, where a highcurrent thermal plasma forms and produces a shockwave [1]. The drawn out initial strike required to remove the concussive shock of a restrike in ceramic joining applications [2] is clearly detrimental to a fast opening switch, and so, the nature of the explosion must be understood and matched to the application.To better visualize the formation of the plasma channels that form across the surface of the film, still images of an exploding film event were taken. A 10.2-cm-long sheet of capacitor grade aluminum metallized film (255-Å-thick aluminum layer deposited on a polypropylene substrate) was connected to copper electrodes spaced 7.6 cm apart. A 2-μF capacitor charged to 2.5 kV was then discharged through the film. A digital SLR camera (Canon EOS 300D with Canon EF-S 18-55-mm lens) set with a 5-s exposure time was used to capture the entirety of the event. Because there was no ambient lighting of the film, the resulting photographs represent the time-averaged light intensity output of the plasma. Since the event is bright, a neutral density filter (ND4) was used in addition to the low aperture settings so that the sensor was not overexposed.It has been established that the discharge circuit's parameters and the specific action integral of a material determine if the energy stored in the capacitor is consumed in the initial strike.Manuscript