Scientists around the world are working on large, doughnut-shaped devices called tokamaks to create fusion energy – a safe, clean and virtually limitless energy source that mimics the power generation process of the sun and stars. 

However, small magnetic field distortions, or ripples, in the tokamaks’ plasma fuel present significant stumbling blocks to developing effective fusion power. Plasma is the fourth state of matter and makes up 99% of the visible universe. The plasma inside a tokamak is supposed to rapidly rotate, but these ripples cause instabilities that slow the motion of the plasma, making it unstable.

Researchers at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics laboratory are using a bit of slight-of-hand called “quasi-symmetry” to get around this problem. Quasi-symmetry was introduced by physicists studying twisty magnetic confinement systems called stellarators. Quasi-symmetry fools the swirling plasma particles by canceling out the magnetic field errors along the path they travel, rendering mostly harmless the disruptive ripples in tokamaks.

“A way to preserve rotation while providing stability is to change the shape of the magnetic field so that the particles are fooled into thinking that they are not moving in a rippled magnetic field,” said PPPL physicist Jong-Kyu Park, lead author of the paper in Physical Review Letters that proposes the solution.