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 1-4% 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. Post-shot simulations with a two-dimensional radiation-hydrodynamics code reproduce well the observed x-ray flux and fluence, backscattered light, and bulk target motion.

Demonstration of a 13-keV KrK-shell x-ray source at the National Ignition Facility

“…We have recently demonstrated [13] a 30% enhancement of the laser-to-x-ray CE for ≈ 4.5 keV x rays from Xe targets at 0.1n cr driven by 70 TW of laser power at the National Ignition Facility (NIF) [14]. The NIF experiments used more than 7× the laser energy and ≈4× the laser power available in previous Xe experiments [11,12] at older lasers.…”

Multi-keV X-ray sources from metal-lined cylindrical hohlraums

“…For the Ti target illuminated by 30 beams, He-and Ly-emission 18002-p. 2 lines are strongly excited showing that both He-like and H-like ionization states were present in the plasma. For the Ti target irradiated by only 10 beams, the Ly-line is still visible but the energy yield Ly-/He-is strongly reduced indicating that the H-like ion fraction is also clearly reduced.…”

“…In particular for ICF related phenomena, x-ray imaging is an important technique to determine density, symmetry, size, interface, and opacity informations concerning high-density objects. Under-dense gaseous targets [1,2] obtained with gas-bags or gas can filled with argon, xenon or krypton, emit multi-keV x-rays with a high laser to x-ray conversion efficiency (CE) but have restricted domains for accessible photon energies. Solid metallic targets [3] enable the creation of sources which span a wider photon energy range but have shown low CE's.…”

Radiochromic film measurement of spatial uniformity for a laser generated x-ray environment

“…[1][2][3][4] We use these and other X-ray sources for materials response studies that require a well-characterized source with respect to energy, time, and space. We report on a simple technique for estimating spatial nonuniformity developed during preparation for recent X-ray source development target shots at the OMEGA laser facility.…”