Species Separation and Hydrogen Streaming upon Shock Release from Polystyrene under Inertial Confinement Fusion Conditions

Persistent Hot-Spot Mix in Cryogenic Direct-Drive Fusion Experiments

We show that an x-ray emission signature associated with acceleration phase mass injection [R. C. Shah et al., Phys. Rev. E 103, 023201 (2021)PRESCM2470-004510.1103/PhysRevE.103.023201] correlates with poor experimental hot-spot convergence and a reduced neutron production relative to expectations. It is shown that with increased target mass as well as with higher-design adiabats, this signature is reduced, whereas with increased debris on the target, the signature is increased. We estimate that the vapor region in typical best designs may have up to 2× the assumed hydrogen mass at the start of deceleration.

Experimental Measurements of Ion Diffusion Coefficients and Heating in a Multi-Ion-Species Plasma Shock

Collisional plasma shocks generated from supersonic flows are an important feature in many astrophysical and laboratory high-energy-density plasmas. Compared to single-ion-species plasma shocks, plasma shock fronts with multiple ion species contain additional structure, including interspecies ion separation driven by gradients in species concentration, temperature, pressure, and electric potential. We present time-resolved density and temperature measurements of two ion species in collisional plasma shocks produced by head-on merging of supersonic plasma jets, allowing determination of the ion diffusion coefficients. Our results provide the first experimental validation of the fundamental inter-ion-species transport theory. The temperature separation, a higher-order effect reported here, is valuable for advancements in modeling HED and ICF experiments.

Full particle-in-cell simulation of the formation and structure of a collisional plasma shock wave

The formation and structure of a collisional shock wave in a fully ionized plasma is studied via full particle-in-cell simulations, which allows the complex momentum and energy transfer processes between different charged particles to be treated self-consistently. The kinetic energy of the plasma flow drifting towards a reflecting piston is found to be rapidly converted into thermal motion under the cooperative effects of ion-ion collisions, ion-electron collisions, and electric field charged-particle interactions. The subsequent shock evolution is influenced by the "precursor" ion beam before a quasisteady state is reached. The shock wave structure is then analyzed from a two-fluid transport viewpoint, which is found to be affected by "flux-limiting" electron transport, the nonthermal ions, and the charge separation electric field.

Observations of anomalous x-ray emission at early stages of hot-spot formation in deuterium-tritium cryogenic implosions

In deuterium-tritium cryogenic implosions, hot-spot x-ray self-emission is observed to begin at a larger shell radius than is predicted by a one-dimensional radiation-hydrodynamic implosion model. Laser-imprint is shown to explain the observation for a low-adiabat implosion. For more-stable implosions the data are not described by the imprint model and suggest there are additional sources of decompression of the dense fuel.