Kr L-shell spectroscopy as a plasma diagnostic for Inertial Confinement Fusion conditions

X-ray spectroscopy is a powerful diagnostic of electron temperature (T e ) and density (n e ) of Inertial Confinement Fusion (ICF) experiments. Mostly, previous applications have been based on K-shell line emission and an argon tracer. However, argon becomes too ionized at electron temperatures higher than 2keV and its line emission weakens. Our research shows that Kr L-shell emission from n=4 to n=2 (from 2700eV to 3200eV photon energy range) is an attractive alternative as a diagnostic of implosion core plasmas with T e in the range of 1 to 3.5keV and n e in the range of 5x10 23 to 2x10 24 /cc. Specifically, Kr atomic number concentrations of order 0.02% produce intense 4-2 lines characteristic of moderate optical depth. We have used the atomic kinetics code ABAKO 1 and PrismSpect 2 to solve the collisional- radiative rate equations self consistently with the radiation transport effect and study the basic properties of the spectrum. In addition, we have employed detailed Stark broadening calculations performed by MERL 3 to obtain the Kr L-shell line profiles. Combining the atomic rates and the electronic level populations obtained with ABAKO and the spectral line shapes from MERL we have created an extensive emissivity and opacity database for the ranges of T e , n e and photon energy of interest. The implosions have been simulated with the 1D Lagrangian hydrodynamics code HYADES 4 for conditions characteristic of a series of direct-drive shots performed at the OMEGA laser facility. Post-processing the HYADES output with the emissivity and opacity database permits to model synthetic data that approximates the expected observations and shows the sensitivity of the spectrum with respect to T e and n e . Also, analysis of the synthetic data demonstrates the usefulness as a temperature and density diagnostic.