National Ignition Facility laser performance status

Abstract

The National Ignition Facility (NIF) is the world's largest laser system. It contains a 192 beam neodymium glass laser that is designed to deliver 1.8 MJ at 500 TW at 351 nm in order to achieve energy gain (ignition) in a deuterium-tritium nuclear fusion target. To meet this goal, laser design criteria include the ability to generate pulses of up to 1.8 MJ total energy, with peak power of 500 TW and temporal pulse shapes spanning 2 orders of magnitude at the third harmonic (351 nm or 3omega) of the laser wavelength. The focal-spot fluence distribution of these pulses is carefully controlled, through a combination of special optics in the 1omega (1053 nm) portion of the laser (continuous phase plates), smoothing by spectral dispersion, and the overlapping of multiple beams with orthogonal polarization (polarization smoothing). We report performance qualification tests of the first eight beams of the NIF laser. Measurements are reported at both 1omega and 3omega, both with and without focal-spot conditioning. When scaled to full 192 beam operation, these results demonstrate, to the best of our knowledge for the first time, that the NIF will meet its laser performance design criteria, and that the NIF can simultaneously meet the temporal pulse shaping, focal-spot conditioning, and peak power requirements for two candidate indirect drive ignition designs.

Cryogenic thermonuclear fuel implosions on the National Ignition Facility

“…The first layered implosion experiments with thermonuclear fuel [15,16] have followed commissioning of the National Ignition Facility (NIF) [17,18] and the demonstration of hohlraum symmetry [19][20][21] with adequate soft x-ray drive [5,22]. In addition, a suite of tuning experiments have been commissioned [6,[23][24][25][26][27][28][29][30] to measure and control [31,32] four key capsule performance parameters: drive symmetry during the foot and the peak of the laser pulse, shock timing, peak implosion velocity, and hydrodynamic mix.…”

“…The fuel is layered in 2.26 mmdiameter CH capsules in a (68 ± 1) µm thick layer; currently, more than 40 % of the layered experiments have been performed with fuel ice layer characteristics that meet the specifications for ignition [33]. Fielding these layers with adequate laser power balance and laser pulse shaping [18] have resulted in near symmetric compression to a sphere with a central hot-spot diameter of 50 µm and a fuel shell of about 80 µm. These indirectdrive implosion demonstrate the highest neutron yields of (7.5 ± 0.1) × 10 14 and areal densities of (1 ± 0.09) g cm −2 achieved to date in laser experiments.…”

Demonstration of Ignition Radiation Temperatures in Indirect-Drive Inertial Confinement Fusion Hohlraums

“…Optical laser backscatter measurements show that these hohlraums absorb 90 % of the incident laser power resulting in radiation temperatures of TRAD = 284 eV and a symmetric implosion to a 100µm diameter hot core. The 192 laser beams of the National Ignition Facility (NIF) [1] have recently been commissioned [2] to deliver the laser energy and power required for heating ignition-scale hohlraums to indirect-drive inertial confinement fusion conditions. Efficient coupling of the laser beams and efficient heating of the hohlraum to radiation temperatures of 270 eV ≤ T RAD ≤ 300 eV are design goals for compressing the fusion capsule in the center of the hohlraum in a rocket-like spherical implosion.…”

Symmetry tuning with megajoule laser pulses at the National Ignition Facility

“…The total laser energy and power delivered by each quad is measured with ±2% and ±3% accuracy, respectively. The beams were smoothed using polarization smoothing, 45 GHz Smoothing by Spectral Dispersion (SSD), and Continuum Phase Plates (CPPs) [14,15]. The incident cone fraction is set to be ∼.33 during the main laser pulse while the actual incident laser pulse is calculated via hydrodynamic simulation.…”