Oxford Centre for High Energy Density Science (OxCHEDS)

Abstract:

Use of the National Ignition Facility to also output frequency-doubled (.53μm) laser light would allow significantly more energy to be delivered to targets as well as significantly greater bandwidth for beam smoothing. This green light option could provide access to new ICF target designs and a wider range of plasma conditions for other applications. The wavelength scaling of the laser plasma interaction physics is a key issue in assessing the green light option. Wavelength scaling theory based on the collisionless plasma approximation is explored, and some limitations associated with plasma collisionality are examined. Important features of the wavelength scaling are tested using the current experimental data base, which is growing. It appears that, with modest restrictions, .53μm light couples with targets as well as .35μm light does. A more quantitative understanding of the beneficial effects of SSD on the interaction physics is needed for both .53μm and .35μm light.

Abstract:

We present an improved analytical expression for the x-ray dynamic structure factor from a dense plasma which includes the effects of weakly bound electrons. This result can be applied to describe scattering from low to moderate Z plasmas, and it covers the entire range of plasma conditions that can be found in inertial confinement fusion experiments, from ideal to degenerate up to moderately coupled systems. We use our theory to interpret x-ray scattering experiments from solid density carbon plasma and to extract accurate measurements of electron temperature, electron density and charge state. We use our experimental results to validate various equation-of-state models for carbon plasmas.