Shiva Star: Pioneering megagauss science and technology

Abstract

The Shiva program at the Air Force Weapons Laboratory developed radiation sources for the purpose of assuring nuclear survivability for defense systems. The program pioneered the use of MJ-class pulsed power systems for simulation of the x-ray radiation environment from a nuclear detonation. The high energy pulsed power development arc culminated in the 9.4 MJ Shiva Star capacitor bank, commissioned in 1982. The reconfiguration drove advancements in capacitor energy density and high-current rail-gap switch design. Modestly updated capacitors and rail-gap switches were integrated into Atlas more than a decade later. Shiva Star enabled many firsts in megagauss high energy density science. With its microsecond rise-time, Shiva Star was designed to function as a laboratory stepping stone to facilitate load development for explosive pulsed power generators producing 50 MA or greater peak current. High-current and high pulse energy were seen as the key performance enablers for weapons simulation, while the machines currently employed in this task reflect recognition of the importance of the radiation pulse duration. High energy density plasma (HEDP) science on Shiva Star initiated with soft x-ray source development based on Z-pinches of gas puff loads and cylindrical foils. The output reached large fractions of the stored energy with pulse widths on the order of 1 μs. In an effort to compress the pulse supplied to the Z-pinch load and thereby reduce the x-ray pulse length, the wire-array plasma flow switch was developed. The plasma flow switch itself represents an unexploited approach to warm x-ray production. HEDP research continued on Shiva Star, exploring several varieties of magnetized target fusion. Initial efforts centered on the MARAUDER concept to produce a compact toroid for eventual compression. About the same time, the research team pioneered the implosion of solid spherical and cylindrical metal shells; material strength stabilized the liners against the onset of the magneto-Rayleigh-Taylor instability, enabling large compression ratios with negligible material blow-off from the inner surface. This work led to a partnership between AFRL and researchers engaged in field reversed configuration (FRC) plasma development at LANL. The venture concentrated on formation, translation, capture, and compression of the high-density, closed field line FRC. The FRC work culminated in the first-ever compressional heating of a high-density, closed field-line plasma target. Shiva Star occupies a unique place in high energy density capability and the components theoretically have significant shot life remaining.