X-ray spectroscopy of L-shell krypton emission*

X-ray spectroscopy of direct- and indirect-drive implosions is a powerful diagnostic of the core plasma conditions achieved in experiments. We discuss the temperature and density dependence of the x-ray line emission of L-shell krypton ions afforded through the characteristic sensitivities of the atomic level populations and charged state distributions and detailed Stark-broadened spectral line shapes due to plasma electric microfields, respectively. We have found that krypton-tracer atomic concentrations in the range from 0.02{\%} to 0.04{\%} of the main fill gas produce krypton L-shell n$=$4-2 line emission with values of optical depth that are less than 1 and intensity comparable to previous observations of argon K-shell spectra. In particular, modeling calculations suggest that L-shell emission of Be- and Li-like krypton ions can be used to diagnose electron temperatures in the 1.5keV to 3keV range in dense implosion cores. Furthermore, since the photon energy ranges of krypton L-shell and argon K-shell emissions are comparable, streaked and imaging spectrometers employed for argon spectroscopy$^{\mathrm{1}}$ can be used for krypton L-shell as well. $^{\mathrm{1}}$D. T. Cliche and R. C. Mancini, Applied Optics \textbf{58}, 4753 (2019).