Gianluca Gregori

Abstract:

This paper presents 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. The theory is used to interpret x-ray scattering experiments from solid density carbon plasmas and to extract accurate measurements of electron temperature, electron density, and charge state. The experimental results are applied to validate various equation-of-state models for carbon plasmas. (C) 2004 American Institute of Physics.

Abstract:

We have measured the production of by 4.7 keV x-rays from low-density Ti-doped aerogel (rho approximate to 3 mg/cc) targets at the OMEGA laser facility (University of Rochester), with the goal of maximizing x-ray output. Forty OMEGA beams (lambda(L) = 0.351 mum) illuminated the two cylindrical faces of the target with a total power that ranged from 7 to 14 TW. The laser fully ionizes the target (n(e)/n(crit) less than or equal to 0.1), and a laser-bleaching wave excites, supersonically, the high-Z emitter ions in the sample. Heating in the target was imaged with gated x-ray framing cameras and an x-ray streak camera. Ti K-shell x-ray emission was spectrally resolved with a two-channel crystal spectrometer and also with a set of filtered aluminum x-ray diodes, both instruments provide absolute measurement of the multi-keV x-ray emission. We find between 40 - 260 J of output with 4.67 less than or equal to by less than or equal to 5.0 keV. Radiation-hydrodynamic calculations predict late time enhancement of the x-ray power due first to axial stagnation of the heating waves, then, ablatively-driven radial compression from the target walls.

Abstract:

We present simplified expressions for the dynamic structure factor, or form factor S(k, omega), which is the quantity describing the inelastic x-ray scattering cross section from a dense plasma or a simple liquid. Our results, based on the random phase approximation (RPA) for the treatment on the charged particle coupling, are compared with analytical expressions for the free electron dynamic structure factor which include effects of strong coupling in both classical and degenerate plasmas. We will show that these modifications introduce minimal corrections to the RPA for typical conditions found in recent non-collective x-ray Thomson scattering experiment on solid density isochorically heated laser plasmas. On the other hand, strong collective scattering may exhibit significant deviations from the RPA. The results shown in this work can be applied to interpreting future x-ray scattering in warm dense plasmas occurring in inertial confinement fusion experiments or for the modelling of solid density matter found in the interior of planets.

Abstract:

A study on the x-ray scattering from solid density plasmas was presented. By applying spectrally resolved multi-keV scattering, the measurements of the microscopic properties of dense matter were demonstrated. The scattering spectra from solid density beryllium demonstrated the inelastic Compton-down shifted feature that is spectrally broadened when heating the solid density plasmas isochorically and homogeneously to temperatures of several times the Fermi energy.

Abstract:

We present the first spectrally resolved x-ray scattering measurements from solid-density plasmas. The scattering spectra show the broadened Compton down-shifted feature allowing us to determine the electron temperature and density with high accuracy. In the low temperature limit, our data indicate that the ionization balance reflects the electrons in the conduction band consistent with calculations that include quantum mechanical corrections to the interaction potential.