Electrothermal instability evolution on Z-pinch rods and imploding liners pulsed with intense current

• Published in: 2016 IEEE International Conference on Plasma Science (ICOPS) p. 1
• Main Authors: Awe, T. J., Yu, E. P., Yelton, W. G., Peterson, K. J., McBride, R. D., Sinars, D. B., Gomez, M. R., Jennings, C. A., Martin, M. R., Rosenthal, S. E., Sefkow, A. B., Slutz, S. A., Vesey, R. A., Yates, K. C., Bauer, B. S., Hutchinson, T. M., Fuelling, S.
• Format: Conference Proceeding
• Language: English
• Published: IEEE 01-06-2016
• Subjects: Diamond; Laboratories; Magnetic confinement; Magnetic resonance imaging; Plasma temperature; Rough surfaces; Surface roughness
• DOI: 10.1109/PLASMA.2016.7534167

Summary form only given. Magnetically imploded liners assemble high-energy-density plasmas for radiation effects and inertial confinement fusion experiments. The stagnation pressures and temperatures achieved are limited by the Magneto-Rayleigh-Taylor (MRT) instability, which can grow to large amplitude from a small seed perturbation. While the metallic liners used for experiments on the Sandia National Laboratories Z Facility are typically diamond turned to 10-30 nm rms surface roughness, the observed MRT amplitude is unexpectedly large. Early in the current pulse an electrothermal instability (ETI), driven by non-uniform runaway Ohmic heating, may provide a mass perturbation on the liner's surface which exceeds the machining roughness; ETI may then provide the dominant seed from which MRT grows. First, data from Z experiments (20 MA in 100 ns) are presented which demonstrate enhanced implosion stability for magnetically accelerated liners that are coated with 70 μm of dielectric. While ETI is not directly observed in these experiments, data and simulation support that the dielectric tamps liner-mass redistribution from ETI, thus limiting the seed amplitude for MRT growth. Second, data from experiments on the U. of Nevada, Reno Zebra Facility (1 MA in 100 ns) are presented. Experiments directly observed the non-uniform temperature and phase-state evolution of the current-carrying surface of 1.0-mm-diameter solid Al rods. The self-emission from micron-scale surface temperature variations were observed directly through high-resolution (3 μm spatial, 2ns temporal) gated optical imaging. Data from aluminum alloys (6061 and 5N) and a variety of fabrication techniques (conventionally machined, single-point diamond turned, electropolished) enable evaluation of which imperfections most effectively seed non-uniform heating and phase changes.