Recent experimental findings indicate that adding boron to a tokamak might help protect the fusion vessel’s walls and stop wall atoms from contaminating the plasma. A new computer modeling approach shows that boron powder may only need to be dispensed from a single point. These findings and the modeling framework will be shared this week during the 66th Annual Meeting of the American Physical Society Division of Plasma Physics in Atlanta.
Researchers working on fusion technology are increasingly favoring tungsten as a prime material for components that interact directly with plasma within fusion reactors known as tokamaks and stellarators. However, the extreme heat from fusion plasma can cause tungsten atoms to break off from the walls and enter the plasma. An excess of tungsten in the plasma can significantly cool it, complicating the maintenance of fusion reactions. Researchers at the U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL) have found that introducing boron powder into the tokamak could address this issue.
Boron provides a partial barrier that shields the reactor walls from the plasma, thereby reducing the influx of wall atoms into the plasma. A new computer modeling framework, developed by PPPL researchers, indicates that applying the boron powder from just one point might be sufficient. The experimental findings and the modeling framework will be discussed this week at the 66th Annual Meeting of the American Physical Society Division of Plasma Physics in Atlanta.
Joseph Snipes, the deputy head of Tokamak Experimental Science, expresses optimism regarding the solid boron injection system based on experiments that showed decreased tungsten sputtering after injecting solid boron. These experiments were performed in three tungsten-walled tokamaks located in Germany, China, and the U.S.
“The boron is sprinkled into the tokamak plasma as a powder, similar to shaking salt from a shaker, which gets ionized at the edge of the plasma and then adheres to the inner walls and exhaust region of the tokamak,” he explained. “Once the walls are coated with a thin layer of boron, it prevents tungsten from entering the plasma and dissipating plasma energy.”
Snipes and his team are developing the boron injection system with the ultimate aim of using it in the ITER Organization’s reactor-scale tokamak. This system is particularly suitable because it allows for boron addition while the machine is running and can accurately manage the quantity of boron injected. The inserted boron layers also retain tritium, a radioactive element whose levels must be controlled in the ITER tokamak to meet nuclear safety standards. This project has seen collaboration from scientists and engineers at ITER and Oak Ridge National Laboratory.
In a separate initiative, Florian Effenberg, a staff research physicist at PPPL, led a project that developed a computer modeling framework for the boron injection system designed for the DIII-D tokamak. Findings from this framework suggest that applying boron powder from one position could produce an adequate distribution of boron across the reactor components simulated.
“We have devised a new way to comprehend how the injected boron interacts within a fusion plasma and its effects on the walls of fusion reactors, aiming to keep them in optimal condition during operation,” Effenberg stated.
The approach adopted by the researchers brings together three different computer models to form a comprehensive framework and workflow. “One model simulates plasma behavior; another tracks the movement and evaporation of boron particles within the plasma, and the third explores how these particles interact with the tokamak walls, including adhesion, degradation, and mixing with other materials,” Effenberg elaborated.
“These insights are essential for refining boron injection methods to ensure effective and uniform conditioning of the walls in ITER and other fusion reactors,” Effenberg noted.
The modeling framework focused on DIII-D, which is managed by General Atomics in San Diego, while future research aims to adapt this framework to ITER. Given that the walls of DIII-D are built from carbon and ITER will use tungsten, investigating the differences in how boron protects the walls will be critical.
Several researchers contributed to the work highlighted by Snipes, including Larry Robert Baylor, Alessandro Bortolon, Florian Effenberg, Erik Gilson, Alberto Loarte, Robert Lunsford, Rajesh Maingi, Steve Meitner, Federico Nespoli, So Maruyama, Alexander Nagy, Zhen Sun, Jeff Ulreich, and Tom Wauters. Funding for this research was provided by the ITER Organization.
Klaus Schmid, Federico Nespoli, and Yühe Feng were involved in developing the modeling framework referenced by Effenberg. Additional contributions to the application of this framework were made by Alessandro Bortolon, Jeremy Lore, Tyler Abrams, Brian Grierson, Rajesh Maingi, and Dmitry Rudakov. The project received funding from DE-AC02-09CH11466, DE-FC02-04ER54698, and DE-AC05-00OR22725.
