A diagnostic platform for measuring mix in inertial confinement fusion experiments using narrowband self-emission imaging

Understanding hydrodynamic mix in inertial confinement fusion (ICF) experiments is vital to improving fusion performance. Spectroscopy of tungsten-doped high-density carbon capsules on the National Ignition Facility shows L-shell emission features associated with different mix mechanisms. This paper describes the development of a diagnostic platform that uses multiple spherically bent crystal optics to produce high-resolution (∼10μm) narrowband (∼7 eV) x-ray images of emission from the capsule hotspot. This technique isolates L-shell emission corresponding to tungsten dopant in different ionization states, providing a high-resolution (≤10μm) image of the tungsten distribution. Since tungsten dopant is initially a component of the capsule ablator, the ability to image the presence of tungsten within the hotspot or the compressed fuel provides a new method of measuring mix. Data are presented from a 1 MJ (laser energy) proof-of-principle experiment, demonstrating that the measurement technique is capable of imaging both tungsten injected deep into the hotspot by the capsule fill-tube and tungsten released into the exterior of the hotspot from the inner region of the doped ablator. Simulation work is presented that explores how this measurement technique might be combined with down-scattered neutron imaging to understand the effect of ice–ablator mix on the burn wave in high-performance ICF experiments.