The energy generated by nuclear fusion has great potential as a clean and almost limitless source of energy, but many obstacles must be overcome before it becomes a practical reality, and scientists may have escaped from another.
New models of an unwanted fusion phenomenon called ‘chirping’, where vital heat can be lost from the reaction process, have given experts a better idea of how it occurs and how to prevent it from happening.
As construction work continues on future fusion reactors, it is good knowledge to have it in the public domain.
The findings apply to a specific type of donut-shaped fusion reactor design called the tokamak, such as the one being built at ITER in southern France. These reactors depend on a delicate balance between the external magnetic fields and the magnetism of the moving plasma to maintain the flow of the entire fusion process.
“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,” says physicist Vinícius Duarte of the Princeton Plasma Physics Laboratory (PPPL).
“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.”
The screech occurs when the frequencies of the high energy plasma waves change, causing the energy and heat to escape, and potentially causing damage to the sides of the tokamak. Thanks to the highly detailed three-dimensional computer simulations produced by the researchers, some of the mechanisms behind that behavior have been identified.
The models showed fast-moving particles in the plasma core hitting rippling waves that flow through the ionized gas. When this happens, groups form that move toward the edge of the plasma stream.
Reassuringly, the models match previous simulations, though the new research adds depth and additional detail to what’s really going on inside the reactor. The end effect is to reduce the efficiency of the tokamak, which is not something you really want when you’re trying to put a next-generation power source to work.
“If you understand it, you can find ways to operate the fusion facility without it,” says physicist Roscoe White.
What scientists try to do with tokamak and other nuclear fusion designs is to mimic the reactions that occur on the Sun, not a small challenge. If we do it right, this process of merging two atomic nuclei into one should give us a way to generate electricity from something as simple as water and salt, with very few waste products.
While the idea is great, it is still a long way from making it work reliably, affordable, and accessible to all. However, there is hope that fusion energy can contribute to the grid in the next 10 years.
The simulations and software processing tools developed by the researchers here were tailor-made for the job, such as “building a microscope” to capture a specific phenomenon in White’s words, and the same models may be used again in the future to analyze and further improve the tokamak design.
“The tools developed in this research have provided insight into the complicated and self-organizing dynamics of chirps in a tokamak,” says Duarte.
The research has been published in the Plasma Physics.
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