Investigation of high X-ray conversion efficiency Kr filled gas sources at the National Ignition Facility

Abstract

We report on the performance of high x-ray fluence Kr K-shell sources that are being developed for high energy density experiments. These targets are 4.1 mm in diameter 4.4 mm tall hollow epoxy tubes having a 40 μm thick wall holding 1.5 atm of Kr gas. For these shots, the National Ignition Facility laser delivered a nominally constant total energy of ≈750 kJ of 351 nm (3ω) light at the three power levels [e.g., ≈120 (low), ≈145 (medium), and ≈210 TW (high)]. The Kr K-shell (Ephoton = 8–20 keV) x-ray radiant intensity and radiant energy (kJ/sr) of these sources were found to increase as a function of laser power but began to plateau at the highest laser power. The Kr K-shell radiant energy increased from ≈1 kJ/sr at ≈120 TW to ≈2 kJ/sr at ≈210 TW. Radiation hydrodynamics simulations predict radiant energies to be always higher than these measurements. The increase in K-shell emission is attributed to its strong dependence on the electron temperature. Electron temperature distributions were inferred from measured Heα and Lyα line emission through the use of a genetic algorithm and Scram modeling. The inferred temperatures from the experiment are 20% to 30% higher than those predicted from modeling.

Testing thermal conductivity models with equilibrium molecular dynamics simulations of the one-component plasma

“…[47] or Ref. [48] for recent examples). The model attempts to include the effects of electron degeneracy as well as the increased collisionality at strong coupling while reproducing the classical Spitzer conductivity scaling in the non-degenerate λ D > a limit [32].…”

A genetic algorithm approach to reconstructing spectral content from filtered x-ray diode array spectrometers

“…While physically meaningful spectra are not necessary to demonstrate the capabilities of the approach, we note that the filtered diode array spectrometers employed on such facilities are meticulously designed to diagnose similar spectral content. For the purposes of this study, we consider 3 test spectra of increasing spectral complexity: (i) non-Planckian continuum emission from a direct-drive exploding-pusher 23 , (ii) non-LTE Xe L-shell (∼ 4 − 7 keV ) source 24 , and (iii) non-LTE Kr K-shell (∼ 13 keV ) source 25 .…”