Fusion researchers are turning to the element tungsten for fusion reactor components, but the intense heat can cause tungsten atoms to ‘sputter’ off and enter the plasma, cooling it down. Researchers at Princeton Plasma Physics Laboratory have found that sprinkling boron powder into the tokamak can help solve this problem. Boron partially shields the reactor wall from the plasma, preventing tungsten from getting into the plasma. This innovative solution could have significant implications for the future of fusion energy. Fusion power and boron are two key topics explored in this blog post.
Capturing Tame Tungsten: The Protective Power of Boron
Scientists working on nuclear fusion tend to progress towards the element tungsten when they search for an ideal material for in-vessel components of a future fusion power plant, as in this case facing the plasma in a device called tokamak or stellarator. Its shiny-prettiness is not what makes it attractive to us either — tungsten resistance to melting and abrasion are. But in a fusion plasma with the extreme heat, tungsten atoms of these walls can then sputter off into the plasma. Too much tungsten in the plasma would cool it greatly, perhaps rendering fusion reactions impractical.
Enter boron, a potential solution. Researchers using the Experimental Advanced Superconducting Tokamak found that injecting several chemical elements like boron power into the tokamak could be a solution to this issue. The purpose of the boron is to act as a shield for the reactor wall from plasma and to keep atoms of the tok material at bay, such as tungsten. This novel concept supports the unique requirements for long-duration fusion by sustaining the necessary plasma conditions.
Sprinkled Boron Powder — A Specific Approach
The researchers demonstrated with a new computer modeling framework that the boron powder could potentially simply be sprinkled from a single location in order to achieve an adequately uniform distribution across the reactor components. This makes for a major improvement in the targeted manner, needing injection of as few boron agents at is possible.
As Joseph Snipes, deputy head for Tokamak Experimental Science explains it, “The boron is simply sprayed into the tokamak plasma as a powder — kind of like salting your food. The powder is ionized at the plasma edge before it adheres to the inner walls and exhaust region of the tokamak. Will the tungsten light up in the plasma as it has D, once it is thin-coated with boron? One of the key advantages of this system is that it can be integrated into existing or new tokamaks at reactor scale, such as those under development and construction by the ITER Organization while still meeting nuclear safety requirements through minimizing tritium presence.
ADVANCED MODELING OF BORON INJECTION strategies
On a different subject, Florian Effenberg, a research physicist in the PPPL staff, released an all-inclusive computer modeling framework of the boron injection system of DIII-D tokamak. The framework unites three distinct computer models to create a novel numerical tool for illuminating the behavior of boron impurities—at once injected into a fusion plasma and also as they interact with the walls of fusion reactors.
The model of the plasma, which tell us about how the plasma behaves; The powder particles in the plasma, from which we can extract information on how fast and under what conditions boron evaporates; The physics in castellations (ridges around the port) that tells us how powder sticks to and erodes from these same surfaces. They are critical for optimizing the boron-injection scheme for providing effective and uniform wall conditioning in ITER and other fusion reactors. This ongoing research1) will be followed by modeling work that scales to the entire ITER tokamak with its tungsten walls in order to ensure the beneficial protective qualities of boron.
