Peter Hansen/Getty Images

Nuclear fusion is deemed the next big thing in the field of energy harvesting for humanity, but creating a reactor that can achieve continuous electricity generation has proved to be a massive technical headache. One of the biggest challenges is the plasma, the superhot state of matter, that is necessary for particles to collide and release energy. Confining this plasma and maintaining the extreme temperature is a crucial step, and also one that has puzzled researchers for years. Now, the National Institute for Fusion Science (NIFS) in Japan claims to have made a breakthrough that enables us to understand the behavior of plasma movements in a nuclear fusion reaction.

Just like airflow turbulence for airplanes, the plasma in a fusion reactor also shows turbulence. Ideally, heat in the plasma should spread evenly, going from the center to the peripheral regions in the containment chamber. However, due to turbulence, the heat can also move to other regions in a rather haphazard manner. For the first time, the team at NIFS detailed the transporter and connector role of plasma turbulence. When gas is heated and turned into plasma, the transporting turbulence carries the heat gradually from the center to the border. The connector plasma turbulence, however, can connect the entire plasma in the chamber in roughly 1/10,000 of a second.

The researchers also noticed that there is an inverse relation between the applied heat and the effects of this connector plasma behavior. Simply put, the shorter the heating time, the stronger the connector plasma turbulence, and as a result, the heat spreads faster. The observations were made within the Large Helical Device (LHD), marking the first time that scientists have been able to experimentally prove the “heat carrier” and “heat connector” roles of plasma in a fusion reactor.

Heat, or high temperature, is the secret sauce for nuclear fusion reactions. The plasma, heated to a temperature of 100 million degrees, must be maintained at that state using superconducting magnets. If it touches the walls of the reactor, it will immediately cool down. Simply put, confining it and maintaining the temperature are extremely important. This is where plasma turbulence can spoil the party. As per experts at the NISF, turbulence can “weaken the confinement by carrying heat outward.” Just over a year ago, the U.S. Department of Energy also highlighted the importance of erratic temperatures in the plasma. The agency described how temperature gradients lead to the creation of plasma islands that can “destroy” the magnetic field. The message is clear. The heat behavior of the plasma must be understood properly. And this is where the latest breakthrough by the NISF comes into the picture. 

Now that the team has a deeper understanding of how heat spreads in the plasma, they can account for the changes brought by the connector and carrier turbulences. And more importantly, they now understand how heating times affect this behavior. This gives scientists a crucial insight that can help more accurately predict the temperature changes in plasma, and accordingly develop heat control methods. Improved control over plasma temperature and heating is a fundamental aspect of achieving a controlled and stable nuclear fusion. 

“This research provides the first unambiguous experimental evidence for the long-hypothesized mediator pathways, validating key theoretical predictions in plasma physics,” the team wrote in a research paper published in the Communications Physics journal. The team says their findings will help predict and control the heat propagation in fusion reactors more effectively, and that they’re now developing a method that can allow more effective control over plasma turbulence.