Mixing in ICF implosions on the National Ignition Facility caused by the fill-tube
C. R. Weber, D. S. Clark, A. Pak, N. Alfonso, B. Bachmann, L. Berzak Hopkins, Thomas L. Bunn, J. W. Crippen, L. Divol, Thomas Dittrich, A. L. Kritcher, O. L. Landen, S. Le Pape, A. G. MacPhee, E. V. Marley, L. Massé, J. L. Milovich, A. Nikroo, P. K. Patel, L. Pickworth, N. Rice, V. A. Smalyuk, Michael Stadermann
Abstract
The micrometer-scale tube that fills capsules with thermonuclear fuel in inertial confinement fusion experiments at the National Ignition Facility is also one of the implosion's main degradation sources. It seeds a perturbation that injects the ablator material into the center, radiating away some of the hot-spot energy. This paper discusses how the perturbation arises in experiments using high-density carbon ablators and how the ablator mix interacts once it enters the hot-spot. Both modeling and experiments show an in-flight areal-density perturbation and localized x-ray emission at stagnation from the fill-tube. Simulations suggest that the fill-tube is degrading an otherwise 1D implosion by ∼2×, but when other degradation sources are present, the yield reduction is closer to 20%. Characteristics of the fill-tube assembly, such as the through-hole size and the glue mass, alter the dynamics and magnitude of the degradation. These aspects point the way toward improvements in the design, some of which (smaller diameter fill-tube) have already shown improvements.