Direct Measurement of Ice-Ablator Interface Motion for Instability Mitigation in Indirect Drive ICF Implosions
A. Do, C. R. Weber, E. L. Dewald, D. T. Casey, D. S. Clark, S. F. Khan, O. L. Landen, A. G. MacPhee, V. A. Smalyuk
Abstract
In indirect drive inertial confinement fusion (ICF) implosions hydrodynamic instability growth at the imploding capsule ablator-DT fuel interface can reduce fuel compressibility and inject ablator into the hot spot hence reducing hot spot pressure and temperature. As a mitigation strategy, a gentle acceleration of this interface is predicted by simulations and theory to significantly reduce this instability growth in the early stage of the implosion. We have performed high-contrast, time-resolved x-ray refraction enhanced radiography (RER) to accurately measure the level of acceleration as a function of the initial laser drive time history for indirect-drive implosions on the National Ignition Facility. We demonstrate a transition from no acceleration to 20±1.8 μm ns^{-2} acceleration by tweaking the drive that should reduce the initial instabilities by an order of magnitude at high modes.