U.S. Department of Energy/Princeton Plasma Physics Laboratory

Picture: PPPL physicists Robert Lunsford (left) and Rajesh Maingi (right) 

Beryllium is a hard silver metal that has long been used in X-ray machines and spacecraft. It is looking for new roles in its quest to bring the energy that drives the sun and stars to the earth. Beryllium is one of the two main materials used for walls in ITER. ITER is a transnational fusion facility built in France to demonstrate the practicality of fusion capabilities. Now, physicists from the U.S. Department of Energy (DOE) Princeton Plasma Physics Laboratory (PPPL) and General Atomics have concluded that injecting tiny beryllium particles into ITER can help stabilize the plasma that fuels the fusion reaction.

Experiments and computer simulations have found that the injected particles help create conditions in the plasma and can trigger small bursts called edge localized modes (ELM). If triggered frequently enough, the micro ELM can prevent huge eruptions that could stop the fusion reaction and damage the ITER facility.

Scientists around the world are seeking to replicate nuclear fusion on Earth to obtain an almost inexhaustible supply of electricity to generate electricity. The process involves plasma, a very hot soup consisting of free floating electrons and atomic nuclei or ions. The merger of atomic nuclei will release a huge amount of energy.

In the current experiment, the researchers injected carbon, lithium, and boron carbide particles (light metals with various properties of beryllium) into the General Atomics' DIII-D national fusion facility operated by the US Department of Energy in San Diego. "These light metals are commonly used materials in DIII-D and have multiple properties with beryllium," said Robert Lunsford, a PPPL physicist who is the first author of the paper, which reports the results of nuclear materials and energy. Because the internal structure of these three metals is similar to that of beryllium, scientists inferred that all of these elements will affect the ITER plasma in a similar way. Physicists also used magnetic fields to make the DIII-D plasma similar to the plasma predicted in ITER.

These experiments are the first of their kind. "This is the first attempt to figure out how these impurity particles penetrate into the ITER, and whether you will sufficiently change the temperature, density and pressure to trigger the ELM," said Rajesh Maingi, head of plasma edge. Co-author of PPPL research and papers. "In fact, this kind of particle injection technology with these elements will really help."

If so, injection can reduce the risk of large ELMs in ITER. "The energy driven into the first wall of the ITER by the spontaneous ELM is sufficient to cause serious damage to the wall," Lunsford said. "If you do nothing, your component life will be unacceptably short, and you may need to replace parts every few months."

Lunsford also used a program he wrote, which showed that beryllium particles injected with a diameter of 1.5 mm (about the thickness of a toothpick) penetrate to the edge of the ITER plasma in a way that can trigger a small ELM. At that size, enough particle surfaces will evaporate or ablate to allow the beryllium to penetrate into the plasma where it can most effectively trigger the ELM.

The next step will be to calculate whether the density change caused by the impurity particles in the ITER actually triggers the ELM, as shown in experiments and simulations. This research is currently being carried out in cooperation with ITER's international experts.

The researchers imagine that the injection of beryllium particles is just one of many tools, including the use of external magnets and the injection of deuterium pellets to manage plasma in annular tokamak facilities such as ITER. Scientists hope to conduct similar experiments on the United European Torus (JET) in the United Kingdom, the world's largest tokamak, to confirm their calculations. Lunsford said, "We think it takes everyone to use a series of different technologies to truly control ELM problems."

The research was published online in February 2019, and was finally printed and published in May 2019.

Support for this work comes from the Office of Science of the U.S. Department of Energy.

Located at the Forestal campus of Princeton University in Princeboro, New Jersey, PPPL is committed to creating new knowledge about plasma physics-supertropical electric gases-and developing practical solutions for the generation of fusion energy. The laboratory is managed by the Office of University Science of the U.S. Department of Energy, which is the largest supporter of basic research in the physical sciences of the United States and is dedicated to solving some of the most pressing challenges of our time. For more information, please visit https://energy.gov/science

The DIII-D National Fusion Facility is the largest magnetic fusion research facility in the United States and has made many pioneering contributions to the development of fusion energy science. DIII-D continues to promote practical fusion energy through key research conducted in collaboration with more than 600 scientists representing more than 100 institutions around the world. For more information, please visit http://www.ga.com/diii-d.

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Rafael Rosen rrosen@pppl.gov Office: 609-243-3317

U.S. Department of Energy/Princeton Plasma Physics Laboratory

Copyright © 2021 American Association for the Advancement of Science (AAAS)

Copyright © 2021 American Association for the Advancement of Science (AAAS)