Beryllium, a hard, silver metal that has long been used in X-ray and spacecraft, plays a new role in finding the power that drives the sun and stars to Earth. Beryllium is one of the two major wall materials in ITER, a multinational fusion facility built in France to demonstrate the practicability of fusion power. Now physicists at the US Department of Energy's Princeton Plasma Physics Laboratory (PPE) and General Atomics have concluded that injecting tiny beryllium pellets into ITER could help stabilize the plasma that drives fusion reactions.
Experiments and computer simulations have shown that the injected granules help create conditions in the plasma that can trigger small eruptions called edge-localized modes (ELMs). If fired enough times, the tiny ELMs prevent huge eruptions that could stop fusion reactions and damage the ITER facility.
Scientists around the world are trying to replicate the fusion on Earth to get a virtually inexhaustible power supply for power generation. The process involves plasma, a very hot soup of free-floating electrons and atomic nuclei or ions. The fusion of the cores releases an enormous amount of energy.
In the present experiments, the researchers injected granules of carbon, lithium and boron carbide ̵
These experiments were the first of their kind. "This is the first attempt to find out how these contaminant pellets penetrate the ITER and whether they can make a sufficient change in temperature, density, and pressure to trigger an ELM," said Rajesh Maingi, head of plasma-edge research at the PPPL and co-author of the paper. "And it actually looks like this granule injection technique would be helpful with these elements."
In this case, injection could lower the risk of large ELMs in ITER. "The amount of energy injected into the first walls of ITER by spontaneous ELMs is enough to severely damage the walls," Lunsford said. "If nothing were done, you would have an unacceptably short life of the components, which might need replacing every few months."
Lunsford also used a program written by himself, which showed that injecting beryllium granules 1.5 millimeters in diameter about the thickness of a toothpick so penetrating the edge of the ITER plasma that small ELMs are triggered could. At this size, sufficient surface area of the granules would evaporate or be removed so that the beryllium can penetrate to sites in the plasma where ELMs can most effectively be triggered.
The next step is to calculate whether density changes are caused by the contaminant pellets in ITER would indeed trigger an ELM, as the experiments and simulations show. This research is currently being carried out in collaboration with international experts at ITER.
The researchers envision the injection of beryllium granules as one of many tools, including the use of external magnets and the injection of deuterium pellets, to manage the plasma in tocamoid plants, such as ITER. Scientists hope to be able to conduct similar experiments with the Joint European Torus (JET) in the United Kingdom, currently the largest tokamak in the world, to confirm the results of their calculations. Lunsford: "We believe that everyone has to work with a variety of different techniques to really get the ELM problem under control."
Device reduces instabilities that can damage the interior of fusion equipment
R. Lunsford et al., Supplemental ELM Control in ITER by Beryllium Granule Injection, Nuclear Materials and Energy (2019). DOI: 10.1016 / j.nme.2019.02.005
Tiny Granules Can Help Bring Clean and Abundant Fusion Force to Earth (2019, July 2)
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