Flux and magnetized plasma compression driven by Shiva Star

Abstract

The AFRL Shiva Star capacitor bank (1300 microfarads, up to 120 kilovolts) operated typically with 4 to 5 megajoules of electrically stored energy, with axial discharge currents of 10 to 15 megamps, and current rise times of approximately 10 microseconds, has been used to drive metal shell (solid liner) implosions in several geometries, including long cylindrical designs, which are suitable for compression of axial magnetic fields to multi-megagauss levels. Such imploding liners are also suitable for compressing magnetized plasmas to magneto-inertial fusion conditions. Magneto-Inertial Fusion (MIF) approaches take advantage of embedded magnetic field to improve plasma energy confinement by reducing thermal conduction relative to conventional inertial confinement fusion (ICF). MIF reduces required implosion speed and convergence ratio relative to ICF. AFRL, its contractors and collaborating institutions LANL, UNM, and UNR have developed one version of magnetized plasmas at pre-compression densities, temperatures, and magnetic fields that may be suitable for such compression. These are Field Reversed Configurations (FRCs). This effort reliably formed, translated, and captured FRCs in magnetic mirrors inside10 cm diameter, 30 cm long, mm thick metal shells or liners in preparation for subsequent compression by liner implosion; imploded a liner with an interior magnetic mirror field, obtaining evidence for compression of 1.36 T field to approximately 500 T; performed a full system experiment of FRC formation, translation, capture, and imploding liner compression operation; identified by comparison of 2D-MHD simulation and FRC capture experiments factors limiting the closed- field lifetime of FRCs to about half that required for good liner compression of FRCs to multi-keV, 1019 ion/cm3, high energy density plasma (HEDP) conditions; and designed and prepared hardware to increase that closed field FRC lifetime to the required amount. Those lifetime extension experiments have obtained imaging evidence of FRC rotation (which is a phenomenon that limits such closed field lifetimes), and of initial rotation control measures slowing and stopping such rotation. These and the results of subsequent closed field plasma lifetime and compression experiments and related simulations will be discussed.