Oxford Centre for High Energy Density Science (OxCHEDS)

Abstract:

The inverse bremsstrahlung (IB) heating rates of a plasma as a function of density and laser intensity were calculated using a molecular dynamic (MD) code. The code belonged to the class of particle-particle-particle-mesh codes. The equations solved by the MD code avoided several assumptions which were inherent to alternative methods. The results of the MD code were compared to previous results for plasmas of low coupling. The results of the calculations for dense, moderately coupled plasmas were also presented. An analytic expression for the IB heating rate, based on a fit to the rates calculated by MD code, was also presented.

Abstract:

The structure of the hot electron beams emitted in laser-solid target interactions was analyzed. It was observed that electron beams were emitted from the rear of thin solid targets irradiated by a high-intensity short-pulse laser. It was shown that the most important condition in which electron beam filamentation due to Weibel-like instabilities become a factor were situations where large regions of low-density plasma exist. The results suggest that Weibel-like instabilities might not be important for the fast-ignitor scheme.

Abstract:

A molecular dynamic (MD) code is used to calculate the inverse bremsstrahlung (IB) heating rates of a plasma as a function of density and laser intensity. The code belongs to the class of particle-particle-particle-mesh codes. Since the equations solved by the MD code are fundamental, this approach avoids several assumptions which are inherent to alternative methods, for example those which employ a Coulomb logarithm, and is not restricted to weakly coupled plasmas. The results of the MD code are compared to previously published results for plasmas of low coupling. The results of calculations for dense, moderately coupled plasmas are also presented. An analytic expression for the IB heating rate, based on a fit to the rates calculated by the MD code, is suggested. This expression includes terms nonlinear in the plasma density.

Abstract:

Ion-acceleration processes were studied in ultraintense laser plasma interactions for normal incidence irradiation of solid targets. Neutron spectroscopy was used for the purpose of analysis. It was found that the ions are preferentially accelerated radially. Results show that the laser pedestal generates a 10 μm scale length in the coronal plasma with a 3 μm scale-length plasma near the critical density.