Simulation study of 3–5 keV x-ray conversion efficiency from Ar K-shell vs. Ag L-shell targets on the National Ignition Facility laser

Abstract

Tailored, high-flux, multi-keV x-ray sources are desirable for studying x-ray interactions with matter for various civilian, space and military applications. For this study, we focus on designing an efficient laser-driven non-local thermodynamic equilibrium 3-5 keV x-ray source from photonenergy-matched Ar K-shell and Ag L-shell targets at sub-critical densities ($n c /10) to ensure supersonic, volumetric laser heating with minimal losses to kinetic energy, thermal x rays and laser-plasma instabilities. Using HYDRA, a multi-dimensional, arbitrary Lagrangian-Eulerian, radiation-hydrodynamics code, we performed a parameter study by varying initial target density and laser parameters for each material using conditions readily achievable on the National Ignition Facility (NIF) laser. We employ a model, benchmarked against Kr data collected on the NIF, that uses flux-limited Lee-More thermal conductivity and multi-group implicit Monte-Carlo photonics with non-local thermodynamic equilibrium, detailed super-configuration accounting opacities from CRETIN, an atomic-kinetics code. While the highest power laser configurations produced the largest x-ray yields, we report that the peak simulated laser to 3-5 keV x-ray conversion efficiencies of 17.7% and 36.4% for Ar and Ag, respectively, occurred at lower powers between $100-150 TW. For identical initial target densities and laser illumination, the Ag L-shell is observed to have տ10Â higher emissivity per ion per deposited laser energy than the Ar K-shell. Although such low-density Ag targets have not yet been demonstrated, simulations of targets fabricated using atomic layer deposition of Ag on silica aerogels ($20% by atomic fraction) suggest similar performance to atomically pure metal foams and that either fabrication technique may be worth pursuing for an efficient 3-5 keV x-ray source on NIF. V C 2015 AIP Publishing LLC.

Beam-path alignment system for high-power laser setups

“…It is also necessary to ensure high accuracy of beam pointing in the far-field. For example, the divergence of beams by 20 μrad leads to a shift in the position of the beam focus on the target by about 180 μm, which is about 2% for an average target size of 10 mm [43] .…”

L-shell X-ray conversion yields for laser-irradiated tin and silver foils

“…In this paper, we report measurements of L-shell emission for Ag foils [17] and compare these to results for Sn foils under the same irradiation conditions. The measurements were taken as a part of experiments on the VULCAN laser at the UK Central Laser Facility, sited at the Rutherford Appleton Laboratory in Oxfordshire.…”

L-Shell X-Ray Conversion Yields for Laser-Irradiated Tin and Silver Foils

“…In this paper, we report measurements of L-shell emission for Ag foils [17] and compare these to results for Sn foils under the same irradiation conditions. e measurements were taken as a part of experiments on the VULCAN laser at the UK Central Laser Facility, sited at the Rutherford Appleton Laboratory in Oxfordshire.…”