A 7.2 keV spherical crystal backlighter system for Sandia's Z Pulsed Power Facility*

Many experiments on Sandia's Z facility, a 30 MA, 100 ns rise-time, pulsed-power driver, use a monochromatic Quartz crystal imaging backlighter system at 1.865\,keV (Si He$_\alpha$) or 6.151\,keV (Mn He$_\alpha$) x-ray energy to radiograph an imploding liner (cylindrical tube) or wire array. The x-ray source is generated by the Z-Beamlet Laser (ZBL), which provides up to 4.5 kJ at 527 nm during a 6 ns window. Radiographs of an imploding thick-walled Beryllium liner at a convergence ratio of about 20 $[$CR $ = R_{in.}(0)/R_{in.}(t)]$ were too opaque to identify the inner surface of the liner with high confidence, demonstrating the need for a higher-energy x-ray backlighter between 6 and 10 keV. We present the design, test and first application of a Ge\,(335) spherical crystal x-ray backlighter system using the 7.242\,keV Co He$_\alpha$ resonance line. The system operates at an almost identical Bragg angle as the existing 1.865 and 6.151\,keV backlighters, enhancing our capabilities such as two-color, two-frame radiography, without changing detector shielding hardware.\\ SAND No: SAND2016-6724 A.