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.

Abstract:

We describe experiments investigating the simultaneous backscattering from 351 nm (3w) and 527 nm (2w) interaction beams in a long scalelength laser-produced plasma for intensities I ≤ 1×1015 W/cm 2. Measurements show comparable scattering fractions for both color probe beams. Time resolved spectra of stimulated Raman and Brillouin scattering (SRS and SBS) indicate the detailed effects of laser intensity, smoothing and plasma parameters on the scattering amplitudes.

Abstract:

We have developed PW(0.5ps/500J) laser system to demonstrate fast heating of imploded core plasmas using a hollow cone shell target. Significant enhancement of thermal neutron yield has been realized with PW-laser heating, confirming that the high heating efficiency is maintained as the short-pulse laser power is substantially increased to near equivalent power to the ignition condition. The efficient heating could be caused by the efficient guiding of heating pulse with the hollow cone and self-organized relativistic electron transport. According to the experimental results, we are now developing a 10kJ-PW laser system to study the ignition-equivalent temperature heating physics.

Abstract:

We have developed a PW (0.5 ps/500 J) laser system to demonstrate fast heating of imploded core plasmas using a hollow cone shell target. Significant enhancement of thermal neutron yield has been realized with PW-laser heating, confirming that the high heating efficiency is maintained as the short-pulse laser power is substantially increased to a value nearly equivalent to the ignition condition. It appears that the efficient heating is realized by the guiding of the PW laser pulse energy within the hollow cone and by self-organized relativistic electron transport. Based on the experimental results, we are developing a 10 kJ-PW laser system to study the fast heating physics of high-density plasmas at an ignition-equivalent temperature.