A team of scientists at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) has developed a new method to measure the amount of heat and particles bombarding the walls of fusion devices, information critical to understanding how to reduce or eliminate the damage to machine components.

The key to the new technique is to measure the amount of light emitted from the walls when they are struck by high-energy particles, such as those found in fusion devices called tokamaks. This method, known as active thermography, will be combined in the future with an infrared thermography camera that already measures how much heat is flowing through the walls.

“For the first time, we can look at heat and particle transport simultaneously on a fusion device,” said PPPL physicist Richard Hawryluk, the project’s principal investigator. “Understanding the heat and particles deposited on the wall materials will help us find out how to optimize reactor performance and lifetime.”

The PPPL scientists collaborated with researchers at the DOE’s Oak Ridge National Laboratory (ORNL), General Atomics, and the Massachusetts Institute of Technology to develop the new technique. The team tested the technique on ORNL’s Joint European Torus (JET), the world’s largest and most powerful tokamak fusion device.

“We were able to use a high-power heating beam to precisely heat a localized spot on the surface of the JET vessel and record the emitted light,” Hawryluk said. “This allowed us to measure the relative contribution of heat and particles to the surface heat loads and determine how the surface heat loads change as we change the plasma conditions.”

The team found that the heat loads were reduced when the plasma was in a high-confinement mode called “H-mode.” This is because the plasma was more stable in H-mode and the heat and particles were more effectively confined to the core of the plasma, reducing the amount of heat and particles reaching the walls.

The new technique provides a valuable tool for studying the plasma-wall interactions in tokamaks. This information is critical to designing and operating fusion devices that can produce electricity without damaging their components.

“This is a very important step forward in understanding how heat and particles are deposited on the plasma-facing surfaces of fusion devices,” Hawryluk said. “This knowledge will help us design future fusion reactors that can operate more efficiently and for longer periods of time.”