high-Z Plasmas Research Articles

Dynamics of high-Z plasmas produced by a short-wavelength laser.

The dynamics and energy flow in Au plasmas produced by a 0.35-\ensuremath{\mu}m laser have been studied with layered targets with 6- and 24-beam spherical illumination from the Omega laser, to understand the processes leading to sub-keV x-ray emission. A significant enhancement in x-ray conversion at low intensities is observed for the 24-beam irradiations with higher energy, greater uniformity, and larger targets. Results are interpreted by comparison with hydrodynamics code calculations. The depth of energy penetration and x-ray emission in the plasma appears to be well understood, but some details of the x-ray time signatures and spectra are not.

Collisional-radiative and average-ion hybrid models for atomic processes in high-Z plasmas.

A new time-dependent atomic model is presented. In the model, called the hybrid-atom model (HAM), the energy-functional form of the population probability obtained from the average-ion model is used to estimate the level population of ions having charge different from the average ion. In medium-Z plasmas HAM gives results similar to the collisional-radiative (CR) model. The required computation time is comparable to the average-ion model even for high-Z plasmas. In these plasmas the CR model becomes impracticable. Though the model partly uses the average-ion model, the x-ray emission calculated is significantly different.

Scaling of high-Z laser plasmas with energy and pulselength

The authors have used LASNEX modelling, which matches most current experiments, to study the scaling of high-Z laser-target interactions to the higher laser energies and longer pulses appropriate to future inertial fusion targets. Results are presented for the irradiation of gold disk targets with 0.26 μm light at a normal incident intensity of 3 × 1014W·cm−2 and incident energy varying from 102J to 107J. For both low- and high-energy cases, steep plasma profiles develop near the critical density of the laser light. In the absence of filamentation, the combination of large electron density gradients at densities substantially below the critical density and strong collisionality due to the high-Z plasma appears to suppress stimulated Raman backscattering and the 2ωpe instability. There is some possibility of stimulated Raman sidescatter in the high-energy case. Using one-dimensional plasma contours, filament generation is strongest at early times for the 107 J case, and weak at all times for the 102 J case. The radiation emission is largely generated near the critical surface, and the conversion efficiencies are of the order of 0.6 and constant to within ±0.1. There is weak variation with energy in global flow parameters.

Opacities of high temperature highZ plasmas

A procedure is described for computation of opacities for highZ plasmas. Bound-bound, bound-free, free-free and scattering processes are considered. The inputs for these have been obtained by solving IEEOS form of Saha’s equation. Detailed calculations of opacities have been done for tungsten and uranium up to 10 keV of temperature.

Current status of laser fusion research at Battelle.

The central research discussed is the analysis and control of laser-produced high-Z plasmas. Research consisting mainly of laser development, model and code development, and target irradiations is described. Some medical applications of the research are also mentioned. (MOW)

Degree of ionization of a high-temperature plasma

An approximate method, originally proposed by Raizer for solving the Saha equations, is extended to both the corona limit, as well as to the more general, non-LTE case, in which both radiative and collisional recombination are important. The method should be useful for obtaining a reliable estimate of the degree of ionization of high-temperature high-Z plasmas.