A team of scientists are trying to determine the “fundamental behaviour of plasma-facing materials with the goal of better understanding degradation mechanisms so we can engineer robust, new materials,” says materials scientist Chad Parish of the Department of Energy’s Oak Ridge National Laboratory. He is senior author of a study in the journal Scientific Reports that explored degradation of tungsten under reactor-relevant conditions.
Because tungsten has the highest melting point of all metals, it is a candidate for plasma-facing materials. Owing to its brittleness, however, a commercial power plant would more likely be made of a tungsten alloy or composite. Regardless, learning about how energetic atomic bombardment affects tungsten microscopically helps engineers improve nuclear materials.
“Inside a fusion power plant is the most brutal environment engineers have ever been asked to design materials for,” Mr Parish says. “It’s worse than the interior of a jet engine.”
Researchers are studying the interaction of plasma and machine components to make materials that are more than a match for such harsh operating conditions. Materials reliability is a key issue with current and new nuclear technologies that has a significant impact on construction and operating costs of power plants. So it is critical to engineer materials for hardiness over long lifecycles.
For the current study, researchers at the University of California, San Diego, bombarded tungsten with helium plasma at low energy mimicking a fusion reactor under normal conditions. Meanwhile, researchers at ORNL used the Multicharged Ion Research Facility to assault tungsten with high-energy helium ions emulating rare conditions, such as a plasma disruption that might deposit an abnormally large amount of energy.
Using transmission electron microscopy, scanning transmission electron microscopy, scanning electron microscopy and electron nanocrystallography, the scientists characterized the evolution of bubbles in the tungsten crystal and the shape and the growth of structures called “tendrils” under low- and high-energy conditions. They sent the samples to a firm called AppFive for precession electron diffraction, an advanced electron crystallography technique, to infer growth mechanisms under different conditions.