Evidence of multi-species ion effects in National Ignition Facility hohlraums using a DT gas-filled platform

Interpenetration and multi-species (MS) ion physics have long been theorized to be important in gas-filled hohlraums on the National Ignition Facility (NIF) [1]. However, until recently, there has been limited ability to diagnose and quantify the dynamics of the hohlraum gas. Not only are MS physics of general scientific interest, understanding hohlraum dynamics is critical to the success of inertial confinement fusion (ICF). Ion behavior influences laser beam propagation, laser-plasma interactions, and capsule implosion symmetry. In this work, we will present results from a novel NIF platform where the hohlraum is filled with fusionable, DT gas. As the hohlraum case, capsule and window ablate and expand, they compress and heat the DT gas within the hohlraum. This generates fusion conditions in the DT gas and produces neutrons. Given that the neutrons are kinematically mapped from the ion distribution, neutron diagnostics are used to infer the ion dynamics. The location of ion stagnation is measured with a novel wide-field-of-view neutron imager, the timing of the stagnation is determined through the burn duration, and ion energy/velocity/temperature distribution functions are inferred through neutron time-of-flight spectrometry. These data constrain our radiation-hydrodynamic hohlraum simulations, which now include a MS physics package, updated opacity models, and higher fidelity hohlraum engineering features. We will show synthetic data from the simulations that illustration how these more physically accurate models are a better representation of the hohlraum dynamics. The neutron observables act as constraints on the simulations and allow us to build confidence in our predictive capabilities. Prepared by LLNL under Contract DE-AC52-07NA27344.

[1] Berzak Hopkins et al., “Near-vacuum hohlraums for driving fusion implosions with high density carbon ablators” Phys. Plasmas 22, 056318 (2015)