Researchers at the Princeton Plasma Physics Laboratory (PPPL) are zeroing in on one cause of the damaging flare ups, or heat bursts, that periodically occur inside fusion reactors known as tokamaks.

This phenomenon, called an “edge localized mode” (ELM), has for years been a major stumbling block in the quest to develop fusion as a viable energy source. It happens when the pressure of hot plasma gas inside the tokamak reaches a critical peak, resulting in an eruption that can damage these intricate and very expensive machines.

But what exactly triggers these ELMs has long been a mystery.

Drawing on data provided by the largest fusion facility in the U.S., the researchers  discovered that the heat bursts sometimes can occur during the recovery phase of a previous ELM burst. A network of energy waves accumulates at the edge of the plasma after an ELM event and exchange energy, releasing damaging bursts of heat.

This research provides fresh insight into what triggers the bursts and how researchers might control them. It also goes a long way in helping scientists to develop fusion as an economically viable, renewable and carbon-free source of energy.