Seeded Magneto-Rayleigh Taylor experiments on planar foils using a 1-MA Linear Transformer Driver

Abstract

Summary form only given. Recent work on the 1-MA Michigan Linear Transformer Driver, MAIZE, has focused on the Magneto Rayleigh-Taylor (MRT) instability and validation of analytic theory, developed at UM (see abstract by Lau et al.). MAIZE is a nominal 1-MA, 100 ns, 100 kV driver, capable of driving 0.1 Ω matched loads. We present here the results of a series of shots using different techniques to seed the MRT instability on planar or pseudo-planar foils. The planar geometry is unique in that it eliminates the complication of the m=0 and m=1 instabilities, allowing extricated analysis of the MRT instability. This work was conducted on 400-nm thick, 1-cm wide aluminum foils placed between two planar or pseudo-planar current return plates. The driver charge was limited to ±70 kV, giving ~700 kA with a risetime of ~150 ns. This reduced charge voltage improved machine and hardware lifetime. Experiments were performed employing various methods to seed the MRT instability on either the foil (cathode) or return current plates (anode). Cathode seeding was performed by imposing a periodic ripple in the foil. Anode seeding was performed by using electrodes with a periodic structure machined into them. The progress of these experiments is presented here. Analysis of MRT was derived from laser shadowgraphic images, obtained using a sub-ns, frequency doubled Nd: YAG laser.