EXPERIMENTAL AND THEORETICAL ANALYSES OF EXPLOSIVELY-FORMED FUSE (EFF) OPENING SWITCHES Douglas G. Tasker, James H. Goforth, Henn Oona, Los Alamos National Laboratory, Los Alamos, NM, USA Gerald Kiuttu, Matthew Domonkos, Air Force Research Laboratory, Albuquerque, NM, USA. ABSTRACT The EFF is used at Los Alamos as the primary opening switch for high current applications. It has interrupted currents from ~10 kA to 25 MA, thus diverting the current into low inductance loads. To understand and optimize the performance of full- scale experiments, many parameters were studied in a series of small-scale experiments, including: electrical conduction through the explosive products; current density; explosive initiation; insulator type; conductor thickness; conductor metal; metal temper; and on. The results show a marked inverse correlation of peak EFF resistance with current density. In this paper we postulate and refute a simple extrusion mechanism of EFF operation; demonstrate that the EFF switch has a near-ideal profile for producing flat-topped voltage profiles; and explore possible mechanisms for the degradation of small scale switch performance. INTRODUCTION The EFF used in high explosive (HE) pulsed power circuits at Los Alamos is a cylindrical switch. The cylindrical design simplifies HE initiation, reduces electrical breakdown problems, and produces a compact device. However, these cylindrical devices are too expensive and complex to use for routine and frequent testing. A small- scale EFF (SSEFF) is used instead for simplicity, and economy. These SSEFFs were designed to match the electrical and physical conditions of the full-scale EFFs. The anvil patterns are identical, and the current densities in most tests are matched to 87 kA/cm. The effects of varying a wide array of parameters have been studied, including: the HE type; the metal foil thickness [1]; the metal type; the metal temper; the current density [2]; the addition of Teflon between the HE and the aluminum; the type of die plastic [1]; the cavity-depth in the plastic die; the cavity shape; the surface finish of the plastic; the time of switch initiation relative to the peak current; and the load inductance [1]. The effects of transient magnetic pressures on SSEFFs will be discussed in this paper. ANALYSIS The SSEFF design comprises the Teflon die, the HE, the aluminum foil, return conductor and insulation, Figure 1. The die is a 19.05 x 165.1 x 165.1.mm Teflon block. A series of 12.7 mm deep, 6.0 mm wide grooves are cut across the block with a center to center spacing of 7.5 mm. This leaves a series of 1.5-mm wide Teflon teeth. The foil is the same as in the large scale EFF, i.e., 812.8-µm thick 6061-T6 aluminum; it is 6.35-cm wide in the SSEFF. The return conductors are 0.5-in. thick, and 6.5-in. wide.