Microengineered Textured Armor for Plasma-Facing Components

Application of nuclear fusion for cost-competitive energy generation cannot be realized until advanced plasma- facing materials and structures are developed. The specific problem addressed in this project is the mitigation of heat-induced failure, surface erosion, and surface blistering of tungsten-based plasma-facing components as a result of the interaction of tungsten with energetic helium and hydrogen isotopes. Ultramet, teaming with Digital Materials Solutions (DMS), the University of California-San Diego (UCSD), and the University of California, Los Angeles (UCLA), as well as EUROfusion, is developing and demonstrating microengineered textured plasma-facing armor for tungsten-based components that is highly tolerant of thermomechanical stress relative to conventional smooth tungsten, and that can efficiently release implanted helium and deuterium ions without blistering. Specifically, structural open-cell tungsten foam (several mm thick) is diffusion-bonded to the divertor surface, followed by vapor deposition of a high surface area textured tungsten coating throughout the foam ligament structure to volumetrically distribute incident radiation. The performance of Ultramet’s textured tungsten foam armor was evaluated through helium plasma testing at the UCSD PISCES facility and through modeling at DMS. Modeling and confirmatory test results showed that textured foam can withstand substantially greater helium fluence levels with reduced damage and possesses greater thermal stress resistance compared with smooth tungsten. The growth rate of tungsten “fuzz” was shown to be substantially lower, while the net sputtering erosion was drastically reduced by a factor of 7. Following continued optimization, it is anticipated that a divertor armor can be developed to substantially increase component lifetime. Textured tungsten foam armor optimization will include fabrication and evaluation of several variants of foam pore size, total porosity, and texture, as well as bonding of the armor to tungsten and heat sink materials. Multiscale/multiphysics modeling of plasma damage and thermomechanical response will be performed by DMS. Performance testing will include multiple iterations of helium plasma exposure testing in the PISCES divertor plasma simulator at UCSD to evaluate armor surface erosion in a fusion plasma-relevant environment. Development specimens and a prototypical divertor submodule will be fabricated and tested in the UCLA HEFTY facility to determine thermostructural operational limits including the maximum heat flux capability. Development specimens will also be provided to EUROfusion which has expressed significant interest in this work and offered to perform high heat flux testing at no cost. Commercial applications and other benefits: With its low generation of radioactive waste, thermonuclear fusion is ideal for large-scale energy generation. Efforts are already in place to complete construction of the International Thermonuclear Experimental Reactor (ITER) with heavy U.S. participation. Practical demonstration of fusion technology is being pursued in the DEMO (European- led) and FNSF (U.S.-led) studies, and the development of advanced materials that can tolerate extreme plasma- generated heat flux is essential to their success. The proposed advanced materials development will also find application in spacecraft electric propulsion systems. Fast-startup, high-current cathode technology utilizing textured foams and coatings has the potential to provide more than an order of magnitude improvement in cathode lifetime and startup time for high-power, high-efficiency electric propulsion.