Turbulent solution to a growing problem

Plasma turbulence, the wildly fluctuating pattern of particle motion, is a concern for fusion energy devices because it allows heat to escape the plasma. However, an even more serious concern is posed by naturally growing magnetic islands that tear the magnetic fabric of the plasma.

The research team performed experiments at the DIII-D National Fusion Facility, operated by General Atomics in cooperation with the U.S. Department of Energy, to study the mutual effect of plasma turbulence and magnetic islands.

"Our team has discovered plasma turbulence gets weaker inside large magnetic islands," explained graduate student and leader of the experiments Laszlo Bardoczi of UCLA. "This leads to islands becoming even larger, which is bad for fusion. However, turbulence can also prevent small islands from growing large. This suggests that we can avoid the growth of harmful magnetic islands by driving turbulence while islands are still small."

The researchers also conducted state-of-the-art computer simulations of the process that replicated the experimental findings. Demonstrating that simulation codes accurately calculate the plasma transport from such processes is vital to developing the ability to predict how fusion plasmas will behave in future experiments.

In future applications, plasma turbulence could be used to prevent small islands from growing and becoming harmful. This will potentially lead to improved control of the islands and therefore efficient operation of fusion devices like ITER, now being built in France as the world's largest tokamak by an unprecedented consortium of 35 nations including the United States. ITER is designed to produce more energy from fusion than it uses to heat the plasma, so understanding how to reduce, or possibly prevent, detrimental island growth could be an important capability.