Observation of interspecies ion separation in inertial-confinement-fusion implosions

TL;DR

This paper provides the first direct experimental evidence of interspecies ion separation in inertial-confinement-fusion implosions, demonstrating ion thermo-diffusion effects in laser-driven fusion experiments.

Contribution

It reports the first direct measurement of interspecies ion separation in ICF experiments using detailed spectroscopy and advanced simulations.

Findings

Observed Ar-atom-fraction enhancement and depletion

Experimental profiles agree with simulations of ion diffusion

Revealed ion separation dynamics during implosion

Abstract

We report direct experimental evidence of interspecies ion separation in direct-drive, inertial-confinement-fusion experiments on the OMEGA laser facility. These experiments, which used plastic capsules with D$_2$/Ar gas fill (1% Ar by atom), were designed specifically to reveal interspecies ion separation by exploiting the predicted, strong ion thermo-diffusion between ion species of large mass and charge difference. Via detailed analyses of imaging x-ray-spectroscopy data, we extract Ar-atom-fraction radial profiles at different times, and observe both enhancement and depletion compared to the initial 1%-Ar gas fill. The experimental results are interpreted with radiation-hydrodynamic simulations that include recently implemented, first-principles models of interspecies ion diffusion. The experimentally inferred Ar-atom-fraction profiles agree reasonably, but not exactly, with calculated profiles associated with the incoming and rebounding first shock.