Long-duration x-ray source development for x-ray diffraction at the National Ignition Facility *

We study the feasibility of producing x-ray sources over timescales relevant to support time-resolved x-ray diffraction (XRDt) measurements during laser-driven dynamic compression experiments at the National Ignition Facility (NIF) [1]. XRDt probes the atomic structure in-situ of transformations at extreme thermodynamic conditions. To record XRD of phase transitions as they occur, we use high-speed (~1 ns) gated hybrid CMOS imagers [2], which provide multiple frames of data over a timescale of a few to tens of ns. To make effective use of these imagers, the x-ray source needs to be temporally and spectrally uniform as long as the sensors remain active.

 

We produce quasi-monochromatic x-ray sources that are either continuous or pulsed by irradiating a 16 µm thick Ge foil with < ~50 kJ of laser energy at an intended intensity of 2x10¹⁵ W/cm². This method produces He-α-like (10.3 keV) radiation [3]. We quantitatively compare the temporally resolved size, shape and intensity of our long-duration x-ray sources to previous backlighters of shorter duration. We also compare our results to theoretical simulations and outline our plans for future investigations of long-duration backlighters.