Newsweek By Hannah Osborne On 9/12/18
Nuclear fusion has the potential to offer almost unlimited clean energy, but harnessing it is extremely difficult. Plasma reaching temperatures of 150 million degrees Celsius needs to be produced by fusing two lighter atomic nuclei to form a heavier nucleus—the same process that powers the Sun.
But like the Sun, the plasma can produce bursts similar to solar flares. This makes confining it stably inside a reactor extremely difficult. If one of these bursts hit the wall of the reactor, they can cause damage and terminate the production of plasma.
Scientists at the Princeton Plasma Physics Laboratory have now found a way to help solve this problem, by eliminating a common instability seen in plasma—known as edge localized modes, or ELMs.
In a study published in Nature Physics, the team looked at ways to control the ELM bursts by disturbing the plasma with magnetic ripples. This reduces the pressure and helps prevent ELMs from happening. To do this they had to find the exact level of magnetic distortion—too little and you get ELMs, too much you end up with other instabilities that potentially cause even more damage.
Jong-Kyu Park and colleagues predicted a set of distortions that could control ELMs without any additional instabilities. They then tested these distortions at the Korean Superconducting Tokamak Advanced Research (KSTAR)—a ring-shaped magnetic fusion confinement device. Their experiments worked.
“We show for the first time the full 3D field operating window in a tokamak to suppress ELMs without stirring up core instabilities or excessively degrading confinement,” Park said. “For a long time we thought it would be too computationally difficult to identify all beneficial symmetry-breaking fields, but our work now demonstrates a simple procedure to identify the set of all such configurations.”
This breakthrough means scientists will be able to better predict the distortions for a far larger tokamak—the ITER, the world’s largest fusion experiment that will take place inside the most complex machine ever built. Being able to control the plasma inside the ITER Tokamak will be essential if fusion energy is to be produced from it. At the moment, scientists believe the ITER Tokamak will start producing plasma in December 2025.
In an interview with Newsweek last year, John Wright, from MIT’s Plasma Science and Fusion Center, said we can expect to see fusion becoming a reality in the coming decades: “With luck, and societal will, we will see the first electricity generating fusion power plants before another 30 years pass. As the plasma physicist [Lev] Artsimovich said: ‘Fusion will be ready when society needs it.’”