A new vision could advance fusion energy

Scientists at the U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL) (PPE) have fostered an understanding of a barrier that can prevent threaded fusion facilities known as tokamaks from operating with high efficiency by losing vital heat.

Led by physicist PPPL Roscoe White, the research team used computers to simulate a type of plasma movement that can strike highly energetic particles from the core to the edge, a phenomenon that could occur at ITER, the multinational tokamak being built. in France to demonstrate feasibility of fusion as an energy source.

“For any fusion device to work, you need to make sure that the highly energetic particles inside it are very well confined within the plasma core,” said PPPL physicist Vinícius Duarte, a member of the research team that reported the results in Plasma Physics. “If those particles move to the edge of the plasma, you can’t keep the plasma in the stable state that is needed to make fusion-powered electricity a reality.”

Duarte refers to a phenomenon called “screeching” that occurs when the frequency of plasma waves that interact with highly energetic particles suddenly changes, causing energy to escape from the plasma core and produce rapidly changing tones. The new findings, which clarify aspects of how the chirp forms in a tokamak, could help researchers figure out how to thwart chirps and maintain vital heat. Preventing sudden frequency changes could also protect the tokamak walls from the sudden release of concentrated and damaging energy bursts.

Fusion combines elements of light in the form of plasma (the hot, charged state of matter composed of free electrons and atomic nuclei) and generates massive amounts of energy in stars. Scientists aim to replicate the fusion in devices on Earth for a virtually endless supply of safe and clean energy to generate electricity.

The researchers used computer simulations that show highly detailed views of the motion of plasma particle clusters to reveal some of the mechanisms responsible for the chirp, giving hope that scientists can find ways to improve its effects. The scientists used the PPPL ORBIT code to calculate how the position and velocity of plasma particles change over time in three dimensions. The simulations showed that the chirp begins when the rapidly moving particles in the nucleus interact with the waves that ripple through the plasma and spontaneously form groups that migrate to the edge of the plasma. The findings confirm previous results based on simplified tokamak configurations; They also reveal richer and more complex dynamics than ever before.

This interaction with the plasma particles causes the frequency of the so-called plasma Alfvén waves to increase and decrease simultaneously, catapulting the groups towards the edge of the plasma and sometimes towards the wall. “The tools developed in this research have provided a glimpse of the complicated and self-organizing dynamics of chirps in a tokamak,” said Duarte.

Scientists had to create new virtual tools to observe the movement of the simulated waves in the necessary details. “The hardest part was inventing diagnostics that would cleanly show what was happening,” said White. “In a sense, it’s like building a microscope that will allow you to see what you need to see.”

The new findings continue a long-standing effort by members of the PPPL Theory Department that focuses on understanding singing, especially within the PPPL Spherical Tokamak National Experiment Update (NSTX-U). “If you understand it,” says White, “you can find ways to operate the fusion facilities without it.”