Demonstration of a 13 keV Kr K-shell X-Ray Source at the National Ignition Facility

We report 3{\%} conversion efficiency of laser energy into Kr K-shell ($\approx$13~keV) radiation, consistent with theoretical predictions. This is $\approx$10$\times$ greater than previous work. The emission was produced from a 4.1 mm diameter, 4 mm tall gas pipe target filled with 1.2 or 1.5~atm of Kr gas. 160 of the NIF laser beams deposited $\approx$700~kJ of 3$\omega$ light into the target in a $\approx$140~TW, 5.0 ns duration square pulse. This laser configuration sufficiently heated the targets to optimize the K-shell x-ray emission. The Dante diagnostics measured $\approx$5~TW into 4{$\pi$} solid angle of $\geq$12~keV x~rays for $\approx$4~ns, which includes both continuum emission and flux in the Kr He$_{\alpha}$ line at 13~keV. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.