Following 50 years of development of the physics and technology required for the initial demonstration of ignition and the recent construction and commissioning of the National Ignition Facility (NIF) in the USA, it is now timely to pursue more focused studies on the many issues associated with post ignition development of Inertial Fusion Energy (IFE) power plants. One key set of areas requiring substantial further study are the myriad issues surrounding the choice of materials to be used within the unique environment of a high temperature, high flux pulsed inertial fusion power plant. Whilst there has been much study into the materials required for advanced nuclear and magnetic fusion energy facilities there is a lack of data, modelling and understanding associated with pulsed operation and the extreme particle fluxes. This CRP seeks to coordinate and encourage focused effort in this area in readiness for inertial fusion plasma ignition.
The overall objective of this coordinated research project is to provide an assessment of the material requirements, consequences and characteristic behaviours in pulsed, repetitively cycled inertial fusion energy systems.
To assess chamber gas/exhaust compositions and the resulting chamber gas wall interactions, with a view to defining self-consistent solutions for an IFE power plant.
To define materials issues associated with integrated facility design, construction, operation, decommissioning and waste management.
To define range of material options and source term implications for IFE capsules using both existing and advanced designs.
To define options for fuel target material choice and mass manufacturing methods, requirements, development pathways and potential solutions.
To define options for first wall thermo-mechanical response and lifetime requirements, development pathways and potential solutions.
To define options for the performance of final optics and lifetime requirements, development pathways and potential solutions.
To investigate the feasibility of existing and newly to be developed irradiation sources to provide testing capabilities in an adequate environment for inertial fusion studies.
To assess material options for Tritium systems with regard to confinement, storage and fuel cycle management.
To specify material requirements for blanket design, their development pathways and impact on the integrated power plant.
To specify material requirements for drivers and their development pathways.
To assess chamber gas/exhaust compositions and the resulting chamber gas wall interactions, with a view to defining self-consistent solutions for an IFE power plant
To assess material options for Tritium systems with regard to confinement, storage and fuel cycle management
To define materials issues associated with integrated facility design, construction, operation, decommissioning and waste management
To define options for final optic performance and lifetime requirements, development pathways and potential solutions
To define options for first wall thermo-mechanical response and lifetime requirements, development pathways and potential solutions
To define options for fuel target material choice and mass manufacturing methods, requirements, development pathways and potential solutions
To define range of material options and source term implications for IFE capsules using both existing and advanced designs
To investigate the feasibility of existing and newly to be developed irradiation sources to provide testing capabilities in an adequate environment for inertial fusion studies
To specify material requirements for blanket design, their development pathways and impact on the integrated power plant
To specify material requirements for drivers and their development pathways
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.
The lack of materials able to withstand the conditions expected in laser-fusion experiments and future reactors, is a major obstacle to achieving thermonuclear ignition. Hence in this CRP, materials more resistant to irradiation and thermal loads were developed and their operational limits were determined, which is of great importance for both IFE and Magnetic Fusion Energy (MFE) reactors, e.g. thermal loads at the divertor in MFE reactors are similar to those expected at the first wall of the IFE reactor.
Likewise, the engineering solutions developed under this CRP in the area of final optics and breeder can be incorporated in advanced IFE reactors.
The computer codes which were developed and validated for measuring the radiation-induced damage in the material, can also be used by the international community for predicting the behaviour of materials under different irradiation conditions.
In addition, the Shock Ignition (SI) scheme is considered to be very promising. Experimental demonstration of shock pressures exceeding 300 Mbar and validation of relevant numerical tool was an important step towards fusion energy production. This project promoted international collaboration within the European IFE community and strengthened collaboration with the US scientists in the framework of the direct drive IFE program. This is an important benefit for the community providing capabilities to design advanced fusion schemes and test them in experiments.
Furthermore, a reliable and economically efficient mass target production technology is one of the major bottlenecks in IFE research. All developed techniques may be integrated into an FST-TL capable of producing about 1 million targets per day. Advanced methods such as the FST-layering technique are important for technology development.
In future IFE reactors, all techniques must be integrated into a Free-Standing Target-Transmission Line (FST-TL) capable of producing about 1 million targets per day. For such purpose, FST-TL was designed operating as a means of a steady-state target-mass-manufacturing device, which is compatible with a noncontact levitating schedule of the target delivery. In this context, the next step will be the creation of the FST-TL for mass manufacturing of IFE targets and their repeatable delivery into the reaction chamber. Then, minimal time and space scales for fabrication and injection processes would allow one to reduce the tritium inventory and to supply targets at the low cost required for economical energy production. This work would also help address some of the key issues for IFE power plant commercialization.