Experimental results indicate that the addition of boron powder into a tokamak could potentially shield the wall of the fusion vessel, preventing atoms from the wall from entering the plasma. This innovative approach, along with a new computer modeling framework, will be presented at the 66th Annual Meeting of the American Physical Society Division of Plasma Physics in Atlanta. Fusion researchers have been exploring the use of tungsten for components that directly face the plasma in fusion reactors. However, tungsten atoms can sputter off under the intense heat of fusion plasma, leading to challenges in sustaining fusion reactions. By sprinkling boron powder in the tokamak, the reactor wall can be shielded from the plasma, ultimately preventing tungsten from entering the plasma and cooling it down.
Researchers at the U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL) conducted experiments that showed a reduction in tungsten sputtering after the introduction of solid boron injection. The experiments took place in three tungsten-walled tokamaks in Germany, China, and the U.S. Joseph Snipes, the deputy head for Tokamak Experimental Science, expressed optimism about the solid boron injection system, emphasizing its potential to mitigate tungsten contamination in the plasma. The boron is sprinkled into the plasma as a powder, ionized at the plasma’s edge, and then deposited on the tokamak’s inner walls, effectively preventing tungsten from radiating away plasma energy.
The boron injection system being developed by Snipes and his team aims to be used in the ITER Organization’s reactor-scale tokamak. The system can add boron while the machine is operational, ensuring precise control and regulation of the injected amount. The deposited boron layers retain tritium, a radioactive element that must be minimized in the ITER tokamak for nuclear safety. Collaboration between scientists and engineers from ITER and the Oak Ridge National Laboratory has been instrumental in advancing this project. Florian Effenberg, a staff research physicist at PPPL, led a separate project to develop a computer modeling framework for the boron injection system in the DIII-D tokamak, showing promising results in achieving uniform distribution of boron across reactor components.
The researchers combined three computer models to create a new framework and workflow to understand the behavior of injected boron in fusion plasma and its interaction with fusion reactor walls. This approach involves simulating plasma behavior, tracking boron powder movement and evaporation, and examining how boron particles interact with tokamak walls. These insights are crucial for optimizing boron injection strategies for effective wall conditioning in ITER and other fusion reactors. The modeling framework initially focused on DIII-D, a tokamak with carbon walls operated by General Atomics, with plans to scale the framework to ITER, which will have tungsten walls. Understanding how boron protects walls in different materials is a key area of research moving forward.
Researchers including Klaus Schmid, Federico Nespoli, and Yühe Feng have contributed to the modeling framework described by Effenberg, aiming to scale the framework to ITER. Funding for this work was provided by DE-AC02-09CH11466, DE-FC02-04ER54698, and DE-AC05-00OR22725. Alessandro Bortolon, Jeremy Lore, Tyler Abrams, Brian Grierson, Rajesh Maingi, and Dmitry Rudakov also participated in applying this modeling framework. The collaborative efforts between experimental results and computer modeling highlight the potential for boron injection systems to protect fusion reactor walls and optimize plasma performance in future fusion technologies.