Design and operation of high energy liner implosions at 16 MA for studies of converging shocks

Abstract

Electromagnetically-driven implosion of soliddensity, cylindrical liners can launch shocks with excellent precision at impact speeds exceeding 5 km/s. We discuss the design and operation of liner implosions driven at peak currents of 16MA, using the Shiva Star capacitor bank at the Air Force Research Laboratory. Liners of 1100 aluminum, with initial length, radius and thickness of 4 cm, 5 cm and 1 mm, respectively, implode under the action of an axial current, rising in 8 �s. Fields on conductor surfaces exceed 0.6 MG. The inner surface of the liner achieves a speed of 6.25 km/s when it impacts a concentric target cylinder of tin at a radius of 2 cm. Magnetic probes and radially-aligned X-radiography follow the motion of the liner and its impact on the tin cylinder. This cylinder holds a solid cylinder of acrylic of 1.5 cm radius in which the motion of a converging shock is followed by optical shadowgraphy and axiallyaligned, X-radiography.Design issues that were successfully addressed include: Pulsed Power -current joints at high magnetic fields in the vicinity of the liner and glideplane/electrodes, where magnetic pressures quickly exceed values for mechanical pre-stress, requiring dynamic solutions; surface temperature enhancements at changes in current direction; possibility of electrical breakdown at connection of liner cassette insulator to bank insulation; need for magnetic inhibition of breakdown (MIB) between liner surface and insulator; Liner Physics -angle needed to maintain current contact between liner and glide-plane/electrode without jetting or buckling; nonlinear magnetic diffusion into liner and associated melting; Diagnostics -X-radiography through cassette insulator and outer conductor without shrapnel damage to film.