Researchers led by Chang Liu of PPPL have unveiled a promising approach to mitigating damaging runaway electrons created by disruptions in tokamak fusion devices. Key to the approach was harnessing a unique type of plasma wave that bears the name of astrophysicist Hannes Alfvén, a 1970 Nobel laureate.
Alfvén waves have long been known to loosen the confinement of high-energy particles in tokamak reactors, allowing some to escape and reducing the efficiency of the doughnut-shaped devices. However, the new findings by Chang Liu and researchers at General Atomics, Columbia University and PPPL uncovered beneficial results in the case of runaway electrons.
The scientists found that such loosening can diffuse or scatter high-energy electrons before they can grow into avalanches that damage tokamak components. This process was determined to be remarkably circular: The runaways create instabilities that give rise to Alfvén waves that keep the avalanche from forming.
"These discoveries provide a comprehensive explanation for the direct observation of Alfvén waves in disruption experiments," said Liu, a staff researcher at PPPL and lead author of a paper that details the results in Physical Review Letters. "The findings establish a distinct link between these modes and the generation of runaway electrons."
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