Ablation Dynamics and Instabilities of Metallic Plasmas Generated UsingMega-Ampere-Scale Current Drivers.

[摘要] This dissertation represents an experimental investigation quantifying the degree of azimuthal correlation between ablating wire cores in wire array Z-pinch loads, as well as a theoretical and experimental investigation of the disruptive magneto-Rayleigh-Taylor (MRT) instability that affects wire array and magnetized fusion concepts.Two experimental configurations were used to investigate correlated ablation between Z-pinch wire cores. The first configuration spaced wires 240 μm apart, a representative spacing for wire array loads fielded on the 26 MA ;;Z-Machine” at Sandia National Laboratories. The second configuration spaced wires 2.47 mm apart or greater, a representative spacing for ~1 MA university scale accelerators. The closely-spaced wires were found to ablate in a strongly correlated manner in both real space and in spatial frequency space. The widely-spaced wires were found to ablate with a similar spatial frequency mode structure, but these modes did not lock in phase. Azimuthal currentshunting and magnetic compression are two possible physical mechanisms for the observed correlation when the wires were spaced closely together.A generalized theoretical treatment of the MRT instability is presented for a planar geometry containing three regions using the ideal magnetohydrodynamic model. Magnetic fields parallel to the interfaces with parallel orientations are included. The densities and magnetic field magnitudes for each region are arbitrary. The generalized dispersion relation, growth rates, feed-through factors, stability conditions, and anisotropy effects are presented. The pressure may originate from an arbitrary combination of kinetic and magnetic pressures. Instability modes with wavevectors parallel to the magnetic field experience a stabilization effect from magnetic tension, whereas modes with wavevectors perpendicular to the magnetic field are unaffected.MRT growth was experimentally investigated using laser images of planar foil loads on the MAIZE facility at the University of Michigan. The construction of this 1 MA linear transformer driver (LTD) facility is documented, as well as experimental measurements of MRT growth on 400 nm aluminum targets. The foil was placed between two current return plates and the position varied to adjust foil acceleration. The measured e-folding times were approximately 100 ns for all cases, approximately 5.6x above theoretical predictions due to plasma expansion.

[发布机构] University of Michigan

[效力级别] Rayleigh-Taylor Instability

[关键词] Plasma Physics;Rayleigh-Taylor Instability;Magneto-Rayleigh-Taylor Instability;Linear Transformer Driver;Electrical Engineering;Nuclear Engineering and Radiological Sciences;Physics;Engineering;Science;Nuclear Engineering & Radiological Sciences