Pathways to Energy from Inertial Fusion: Materials Beyond Ignition

Fusion R&D suffers from lack of materials able to withstand conditions expected in fusion reactors. Hence, this CRP provided the possibility for development and qualification of advanced candidate materials for future nuclear fusion reactors, namely nanostructured W, heavy tungsten alloys, double forged tungsten and double forged W Ta alloy, CNT for first wall, diverse high quality steels (ODS, AISI 316L stainless and Eurofer) for structural material, SiO2, fused silica, embedded nanoparticles in Silica, high-purity calcium fluoride for final optics, and nanostructured W and SiC coatings for permeation and corrosion barrier.
Numerical models describing the nonlinear processes of laser energy absorption and electron transport were implemented in the large-scale radiation hydrodynamic code CHIC thus providing a reliable basis for the improved target designs in direct drive ignition schemes. Performance of newly designed targets can be verified on the existing high energy laser facilities.
The fuel Free Standing Target (FST)-layering within free-standing and line-moving targets presents a credible pathway to a reliable, consistent, and economically efficient target supply for Inertial Fusion Energy (IFE) power plants. A fundamental difference of the method from the generally accepted approaches is that it works with line-moving targets, and the targets cooperate all production steps in the FST-Transmission Line (FST-TL) of repeatable operation. The method provides the fuel filling and then cryogenic layering in an isotropic ultrafine state because the fuel must be isotropic in order to assure that fusion takes place.
In the SI IFE approach the main driving pulse of ~ 10^14 W/cm2 intensity and of several tens of nanosecond pulse (long pulse) is followed by a powerful final spike of hundred picoseconds duration (short pulse) with a peak intensity ~ 10^16 W/cm2, which uploads a convergent shock wave and ignites the collapsed thermonuclear fuel. An appropriate laser pulse form is rather difficult to maintain in a quasi-steady amplification of the pulse stack in an angular multiplexing scheme due to its high saturation of KrF amplifiers by high-power spikes. As a result, the alternative way that was developed combines short and long pulses immediately on a target while being simultaneously amplified in the same amplifier chains due to the short gain recovery time of KrF laser. Then, to ensure reliable and efficient long-time repetition rate operation of e-beam-pumped KrF laser driver, nonlinear effects of high-power radiation self-focusing can be avoided by using Kerr defocusing of filaments in Xe. Last, coloration of amplifier windows under irradiation by fast electrons and bremsstrahlung x-rays can be reduced by colour centre temperature annealing or bleaching by UV irradiation.
Equally important, Stimulated Brillouin Scattering (SBS) Phase Conjugate Coherent beam combination has an effect on the way to develop real laser driver module to produce 25 kJ/10 ns/10 Hz output for IFE implosion by combining 25 modules of 1 kJ/10 Hz laser that is currently available to produce with current laser technology. Besides, this technique is also applicable to ultra-high-power ns, ps, and fs laser development that can be used for particle acceleration, laser peening, laser machining, and laser space debris removal.
Additionally, the obtained results in free standing cryogenic target fabrication and transmission line will allow engineering and mosaic building of the FST-TL for testing reactor technologies., which are applicable to mass target production and their repeatable delivery into the reaction chamber, and to identify the key issues in IFE commercialization. Implementation of the FST-TL program will be useful for working-out and substantiating the technical requirements needed for future IFE power plants.
Furthermore, results from PF-6 contributed to the understanding of neutron irradiation effects at IFE reactor-relevant level.
Finally, table top repetitive irradiators based on miniature plasma focus technology, are low cost devices useful to study plasma facing materials for both types of reactors: inertial and magnetic fusion. With this kind of table top and low-cost irradiator, the plasma facing materials research could be highly enhanced.