We report measurements of x-ray scattering cross sections for dense plasmas created by subjecting aluminum foils to strong laser-driven shocks. A narrow cone of quasimonochromatic x-rays at approximately 4.75 keV was used to probe the shocked part of the foil and scattered photons were detected with a CCD camera. The scattering cross section shows a clear peak, indicating diffraction from the plasma. Analysis and simulation of the data suggest that radiative heating and electron-ion energy exchange are important factors in the plasma production.

A method for the self-consistent solution of the hydrodynamic, excitation and ionization equations describing a laser-produced plasma is presented. The coupling of atomic processes and the free electron energy balance equation in a one-dimensional Lagrangian model is described. Transitions between excited as well as the ground states are included within the average-atom approximation. The resulting model is used to calculate ionization and population inversion in Delta n not=0 recombination X-ray laser experiments. With the addition of a steady-state collisional radiative model for Delta n=0 transitions, collisional X-ray lasers have also been modelled.

Fast electron generation and propagation were studied in the interaction of a green laser with solids. The experiment, carried out with the LULI TW laser (350 fs, 15 J), used K(alpha) emission from buried fluorescent layers to measure electron transport. Results for conductors (Al) and insulators (plastic) are compared with simulations: in plastic, inhibition in the propagation of fast electrons is observed, due to electric fields which become the dominant factor in electron transport.

No abstract

Exploiting the high absorption efficiency of intense, ultrashort laser pulses in gases of atomic clusters we have created plasma filaments with temperatures of .1 keV and electron densities in excess of 10 20 cm 23 . Using picosecond laser pulses, we have interferometrically measured the temporal and spatial evolution of the electron density in these plasmas on a fast ͑,50 ps͒ time scale. Our measurements indicate that nonlocal heat transport by hot electrons drives a fast ionization wave, and the data agree well with a nonlocal heat transport model. [S0031-9007(97)

We have developed and implemented the Relational Grid Monitoring Architecture (R-GMA) as part of the DataGrid project, to provide a flexible information and monitoring service for use by other middleware components and applications.R-GMA presents users with a virtual database and mediates queries posed at this database: users pose queries against a global schema and R-GMA takes responsibility for locating relevant sources and returning an answer. R-GMA's architecture and mechanisms are general and can be used wherever there is a need for publishing and querying information in a distributed environment.We discuss the requirements, design and implementation of R-GMA as deployed on the DataGrid testbed. We also describe some of the ways in which R-GMA is being used.

We analyze recent experimental results on the increase of fast electron penetration in shock compressed plastic [Phys. Rev. Lett. 81, 1003 (1998)]. It is explained by a combination of stopping power and electric field effects, which appear to be important even at laser intensities as low as 10(16) W cm-2. An important conclusion is that fast electron induced heating must be taken into account, changing the properties of the material in which the fast electrons propagate. In insulators this leads to a rapid insulator to conductor phase transition.

The time-integrated x-ray emission from a hot, dense iron plasma has been recorded. The iron plasma was created when a target with a 1000-Å-thick iron layer buried beneath 1000 Å of plastic was irradiated by a 300 fs pulse of 249 nm laser light at an intensity of approximately 1017 W cm−2. Two models have been used to construct a synthetic x-ray spectrum. The first employs detailed, spectroscopically accurate atomic data and the second uses a local thermodynamic equilibrium opacity model. The detailed model shows fairly good agreement with experiment whereas the opacity model only shows agreement in the gross features.