The installation of the first piece of the ITER tokamak reactor. (ITER Organization/EJF Riche)
Energy generated from nuclear fusion holds plenty of potential as a clean and almost limitless source of power, but many obstacles need to be overcome before it’s a practical reality – and scientists may have just clambered over another one.
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 stop it from happening.
As construction work on the fusion reactors of the future continues, that’s good knowledge to have in the public domain.
The findings apply to a specific doughnut-shaped type of fusion reactor design called a tokamak, like the one being built at ITER in southern France. These reactors rely on a delicate balance between external magnetic fields and the moving plasma’s own writhing magnetism to keep the entire fusion process flowing.
“For any fusion device to work, you need to make sure that the highly energetic particles within it are very well confined within the plasma core,” says physicist Vinícius Duarte from the Princeton Plasma Physics Laboratory (PPPL).
“If those particles drift to the edge of the plasma, you can’t sustain the steady-state burning plasma needed to make fusion-powered electricity a reality.”
Chirping occurs when the frequencies of the high-energy plasma waves change, causing 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 researchers, some of the mechanisms behind that behaviour have been identified.
The models showed fast-moving particles in the core of the plasma hitting undulating waves flowing through the ionised gas. When this happens, clumps form that move towards the edge of the plasma stream.
Reassuringly, the models match up with previous simulations, though the new research adds extra depth and detail to what’s actually going on inside the reactor. The ultimate effect is to reduce the efficiency of the tokamak, which isn’t something you really want when you’re trying to get a next-gen power source up and running.
“If you understand it, you can find ways to operate fusion facilities without it,” says physicist Roscoe White.
What scientists are trying to do with the tokamak and other nuclear fusion designs is to mimic the reactions happening on the Sun – no small challenge. If we get it right, this process of fusing 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 a great one, getting it to work in a way which is reliable, affordable, and accessible to everyone is still some way off. Nonetheless, there are hopes that fusion energy could be contributing to the grid within the next 10 years.
The simulations and software processing tools developed by the researchers here were custom-made for the job – like “building a microscope” to capture one specific phenomenon in White’s words – and the same models can be used again in the future to further analyse and improve the tokamak design.
“The tools developed in this research have enabled a glimpse into the complicated, self-organised dynamics of the chirps in a tokamak,” says Duarte.
The research has been published in the Physics of Plasmas.