Experimental Demonstration of Dynamical Similarity of the Preseeded Magneto-Rayleigh-Taylor Instability in Scaled Z-Pinch Implosions.

With the achievement of thermonuclear ignition, there is interest to increase the performance of inertial-confinement-fusion (ICF) systems to reach high fusion yields and high-energy gain for energy-production purposes. One approach to achieve this is magnetic-direct-drive (MDD) ICF, where magnetic fields are used to compress ICF targets to thermonuclear conditions. To study the scaling of MDD ICF to high yields, we performed experiments on the 20-MA, 100-ns Z machine to study the invariant behavior of the magneto-Rayleigh-Taylor instability when changing the magnetic-field drive. Similarity-scaled aluminum cylindrical shells with preseeded axial perturbations were imploded at two different maximum currents: 14.7 and 19.2 MA. Consistent with dynamical similarity within experimental uncertainties, the magneto-Rayleigh-Taylor growth history measured via x-ray radiography exhibits agreement at the 16% level or better for late-time growth factors of 10x to 50x. However, the early instability development is not dynamically similar due to Ohmic-heating effects, which are not conserved by the proposed scaling prescriptions. This Letter exemplifies the application of similarity scaling to rigorously investigate the scaling of MDD ICF to high yields.