Multi-keV x-ray source development experiments on the National Ignition Facility

Abstract

We report results from a five shot campaign carried out with Ar–Xe gas-filled targets at the National Ignition Facility (NIF). The targets were shot with ≈350 kJ of 3ω laser energy delivered with a 5 ns trapezoidal laser pulse. We report measured x-ray output from the target in different spectral bands both below and above 1.5 keV photon energies: We find yields of ≈20.5 kJ/sr with peak x-ray power approaching 4 TW/sr over all energies, as measured for the unique viewing angle of our detector, and ≈3.6 kJ/sr with peak x-ray power of 1 TW/sr for x-rays with energies >3 keV. This is a laser-to-x-ray conversion efficiency of 13±1.3% for isotropic x-rays with energies >3 keV. Laser energy reflected by the target plasma for both inner and outer-cone beams is measured and found to be small, between 1% and 4% of the drive energy. The energy emitted in hard x-rays (with energies >25 keV) is measured and found to be ≈1 J/sr. Two-dimensional imaging of the target plasma during the laser pulse confirms a fast, volumetric heating of the entire target, resulting in efficient laser-to-x-ray conversion. Postshot simulations with a two-dimensional radiation-hydrodynamics code reproduce well the observed x-ray flux and fluence, backscattered light, and bulk target motion.