Fusion, the power that drives the sun and stars, produces massive amounts of energy. Scientists here on Earth seek to replicate this process, which merges light elements in the form of hot, charged plasma composed of free electrons and atomic nuclei, to create a virtually inexhaustible supply of power to generate electricity in what may be called a "star in a jar."
A long-time puzzle in the effort to capture the power of fusion on Earth is how to lessen or eliminate a common instability that occurs in the plasma called edge localized modes (ELMs). Just as the sun releases enormous bursts of energy in the form of solar flares, so flare-like bursts of ELMs can slam into the walls of doughnut-shaped tokamaks that house fusion reactions, potentially damaging the walls of the reactor.
To control these bursts, scientists disturb the plasma with small magnetic ripples called resonant magnetic perturbations (RMPs) that distort the smooth, doughnut shape of the plasma -- releasing excess pressure that lessens or prevents ELMs from occurring. The hard part is producing just the right amount of this 3D distortion to eliminate the ELMs without triggering other instabilities and releasing too much energy that, in the worst case, can lead to a major disruption that terminates the plasma.
Making the task exceptionally difficult is the fact that a virtually limitless number of magnetic distortions can be applied to the plasma, causing finding precisely the right kind of distortion to be an extraordinary challenge. But no longer.
Physicist Jong-Kyu Park of the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL), working with a team of collaborators from the United States and the National Fusion Research Institute (NFRI) in Korea, have successfully predicted the entire set of beneficial 3D distortions for controlling ELMs without creating more problems. Researchers validated these predictions on the Korean Superconducting Tokamak Advanced Research (KSTAR) facility, one of the world's most advanced superconducting tokamaks, located in Daejeon, South Korea.
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