Laser Inertial Fusion Energy Power Research Articles

Testing IFE materials on Z

On a single-pulse basis, the tungsten armor for the chamber walls in a laser inertial fusion energy power plant must withstand X-ray fluences of 0.4–1.2 J/cm 2 with almost no mass loss, and preferably no surface changes. We have exposed preheated tungsten samples to 0.27 and 0.9 J/cm 2 X-ray fluence from the Z accelerator at Sandia National Laboratories to determine the single-shot X-ray damage threshold. Earlier focused ion beam analysis has shown that rolled powdered metal formed tungsten and tungsten alloys, will melt when exposed to 2.3 J/cm 2 on Z, but not at 1.3 J/cm 2. Three forms of tungsten – single-crystal (SING), chemical-vapor-deposited (CVD), and rolled powdered metal (PWM) – were exposed to fluence levels of 0.9 J/cm 2 without any apparent melting. However, the CVD and PWM sample surfaces were rougher after exposure than the SING sample, which was not roughened. BUCKY (1D) calculations show a threshold of 0.5 J/cm 2 for melting on Z. The present experiments indicate no melting but limited surface changes occur with polycrystalline samples (PWM and CVD) at 0.9 J/cm 2 and no surface changes other than debris for samples at 0.27 J/cm 2.

Neutron and gamma ray heating in the grazing incident liquid metal mirrors for laser inertial fusion energy power plants

A thin film of liquid metal can serve as final optics of a laser inertial fusion energy (IFE) power plant. Calculations of pulsed neutron and gamma-ray heating are presented for a grazing incident liquid metal mirror (GILMM) used for robust final optics of a laser IFE power plant. Different liquid films (Li, Na, Mg, Al, Si, K, Ga, Ag, Au, Pb, Bi and Flibe “Li 2BeF 4”) are considered at a distance of 30 m from a nominal 1 GJ fusion source as well as different substrate materials (SS-304 and SiC). The effect of neutron heating both in the liquid metal film as well as in the subsrate material will be by around three to four orders of magnitude lower than the laser heating limit. Hence the nuclear heating will not be a limiting factor for grazing incident liquid metal mirror (GILMM) of a laser IFE power plant.

Grazing incidence liquid metal mirrors (GILMM) for radiation hardened final optics for laser inertial fusion energy power plants

A thin film of liquid metal is suggested as a grazing incident mirror for robust final optics in a laser inertial fusion energy (IFE) power plant. The amount of laser light the grazing incidence liquid metal mirror (GILMM) can withstand, called the damage limit is limited by the surface disturbances initiated by rapid laser heating. For 0.35-μm light, the damage limit for a sodium film 85° from normal is calculated to be 57 J/cm 2 normal to the beam for a 20 ns pulse and 1.3 J/cm 2 for a 10-ps pulse (2 and 90 m 2 of mirror area per 100 kJ of laser energy at 20 ns and 10 ps, respectively). Feasibility relies on keeping the liquid surface flat to the required accuracy by a combination of polished substrate, adaptive (deformable) optics, surface tension and low Reynolds number, laminar flow in the film. The film's substrate must be polished to ±0.015 μm. Then surface tension keeps the surface smooth over short distances (<10 mm) and low Reynolds number laminar flow keeps the surface smooth (disturbances less than ±0.01 μm) over long distances (>10 mm). Adaptive optics techniques keep the substrate flat to within ±0.06 μm over 100-mm distance and ±0.6 μm over 1000 mm distances, even after 30 years of cumulative damage via neutron irradiation. The mirror can stand the X-ray pulse when located 30 m away from the microexplosions of nominal yield of 400 MJ (50 MJ of X-rays) when Li is used, but for higher atomic number liquids like Na there may be a significant rise in temperature, forcing the use of other X-ray attenuation methods such as attenuation by xenon gas. The GILMM should be applicable to both direct and indirect drive and pulse lengths appropriate to slow compression (∼20 ns) or fast ignition (∼10 ps). For direct-drive laser beams near the poles (70°, where 90° is vertical), stable thin films become more challenging. Proof of the concept experiments are needed to verify the predicted damage limit and required smoothness.