Seeded Magneto Rayleigh-Taylor instability driven by a 1-MA Linear Transformer Driver

Abstract

Experimental, theoretical and simulation research investigations are underway on the Magneto Rayleigh-Taylor instability driven by the Mega Ampere Linear Transformer Driver at the University of Michigan. Since the Linear Transformer Driver operates at 100- kV output, inductance minimization was crucial in design of the coaxial and radial magnetically insulated transmission line that transmits power to the load. Experiments ablate a 400 nm-thick, 1 cm wide, planar, aluminum foil located between two parallel-plate anodes. The initial position of the foil relative to the anodes controls the foil-plasma acceleration. Laser-micromachined, periodic hole patterns on foils are utilized to seed the wavelength of Magneto Rayleigh-Taylor growth. Sub-ns laser shadowgraphy diagnoses the instability growth at the edges of the ablation plasma. Early instability is believed to originate from the Electro-Thermal instability. Later exponential growth rates have been measured whose trends are consistent with Magneto Rayleigh Taylor theory. As expected, the fastest Magneto Rayleigh-Taylor growth rate corresponds to the largest foil-plasma acceleration. Effects of magnetic shear on Magneto Rayleigh-Taylor growth have been predicted theoretically.