Products from Nuclear Fusion will Make Fusion Easier

High energy ions in plasma generated for fusion energy production will help confine energy produced by fusion by stabilizing turbulence inside that plasma

Article | Spring 2022

“Can we achieve fusion energy in our lifetimes?” Nuclear fusion energy has long been considered the ultimate energy source because it would be clean, safe, and almost unlimited. However, fusion energy is still in the research stage. Some even joke that this energy resource will always be 30 years in the future. However, it now is indeed possible that fusion will be fully and finally realized within the next 30 years.

Last year, for the first time, fusion scientists generated plasma with a 100 million K ion temperature for 30 seconds in the KSTAR Tokamak, a fusion device operated by the Korea Institute of Fusion Energy (KFE). 100 million K is the temperature required for successful commercial fusion energy production. KAIST researchers in collaboration with research teams from Seoul National University and KFE have determined that this high temperature can be achieved through nonlinear interaction between high energy ions and the turbulence inside fusion plasmas.

For fusion energy production, as many high energy particles as possible should be confined for as long as possible. The temperature necessary to achieve fusion is approximately 100 million K, at which all particles become ionized, and fusion occurs in the plasma state. Once sufficient confinement is achieved, the next requirement is self-sustainment of high-density hot plasma using fusion products, i.e., high energy ions. In the ideal case, these high energy ions generated by fusion will heat the plasma via collisions.

However, there is no guaranteed way to slow down this process because two opposite effects are expected. First, high energy ions can induce instability, which will enhance transport. Second, these ions can stabilize turbulence, the main transport mechanism in fusion plasmas, thereby reducing transport. A simulation run by the KAIST team led by Professor Sung demonstrated that the latter effect was dominant in the KSTAR experiment, reducing transport and thereby allowing the high temperature plasma to last for 30 seconds.

The movie shows that the high temperature region is formed near the center of the plasma and is sustained because the energy is confined inside the plasma. In other words, a transport barrier forms inside the plasma. The simulation shows that as the temperature of the high energy ions increases, the turbulence structure is chopped in a radial direction. This chopping occurs due to nonlinear interaction between high energy ions and turbulence existing in the fusion plasma. Experimental results also show a transport barrier inside the plasma.

This finding implies that fusion products may actually facilitate the condition required for fusion energy production, which is indeed major news for those awaiting the era of fusion energy. One European group showed similar findings; however, their plasmas were heated by waves, while the KSTAR plasmas were heated by a neutral beam. The KSTAR results thus show great promise for achieving fusion energy in the near future. Further, the experimentally consistent results support the current predictive capability of fusion plasma performance.