Redesigning the electric gun: Launching thick flyers to hypervelocity with high efficiency

Abstract

To investigate pressure states as extreme as those involved in inertial confinement fusion using projectile-driven impact, the projectile must be both moving at hypervelocity and thick enough to introduce a shock pulse sufficiently long as to be measured. The electric gun is a highly efficient pulsed-power projectile launcher: its unique drive mechanism has been reported to convert over 25% of a capacitor bank’s stored electrical energy to flyer kinetic energy (Osher et al., 1990). This high efficiency allows the gun to accelerate thin dielectric flyers to hypervelocity using relatively low energy machines (Weingart et al., 1979). However, the technique was unable to accelerate thick flyers (>0.5 mm) without causing the flyers significant damage, rendering it unsuitable for investigating extreme states of matter. In this work, previously existing results from the launch of a thin flyer on a low energy machine were analysed using a 0D electric gun model (Fitzgerald et al., 2023). The pressure states experienced by the flyer during this shot, performed in a well understood region of the electric gun parameter space, were used to inform the design of a new electric gun load, capable of launching thick flyers to hypervelocity. The experimental results of the testing of this load design on a 140 kV, 2.0µs rise-time machine are presented. The load was found to successfully accelerate intact flyers up to 2.0-mm-thick, introducing shock speeds of over 10 km/s in a PMMA target block, inducing pressures of 80 GPa. This is twice as thick as those reported previously (Song et al., 2018). The outcomes of the study suggest the results from previous low-risk shots can be used to develop electric gun loads in new regions of the design space using simplified modelling tools.