Return of the Blob: Surprise link found to edge turbulence in fusion plasma

Image showing spiraling magnetic field fluctuations at the edge of the NSTX tokamak.
Credit: Physics of Plasmas. Composition by Elle Starkman/Office of Communications.

Blobs can wreak havoc in plasma required for fusion reactions. This bubble-like turbulence swells up at the edge of fusion plasmas and drains heat from the edge, limiting the efficiency of fusion reactions in doughnut-shaped fusion facilities called “tokamaks.” Researchers at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) have now discovered a surprising correlation of the blobs with fluctuations of the magnetic field that confines the plasma fueling fusion reactions in the device core.

New aspect of understanding

Further investigation of this correlation and its role in the loss of heat from magnetic fusion reactors will help to produce on Earth the fusion energy that powers the sun and stars. “These results add a new aspect to our understanding of the  edge heat loss in a tokamak,” said physicist Stewart Zweben, lead author of a paper in Physics of Plasmas that editors have selected as a featured article. “This work also contributes to our understanding of the physics of blobs, which can help to predict the performance of tokamak fusion reactors.”

Fusion reactions combine light elements in the form of plasma—the hot, charged state of matter composed of  and  that makes up 99 percent of the visible universe—to produce massive amounts of energy. Scientists are seeking to create and control  on Earth as a source of safe, clean and virtually limitless power to generate electricity.

PPPL researchers discovered the surprising link last year when re-analyzing experiments made in 2010 on PPPL’s National Spherical Torus Experiment (NSTX)—the forerunner of today’s National Spherical Torus Experiment-Upgrade (NSTX-U). The blobs and fluctuations in the magnetic field, called “magnetohydrodynamic (MHD)” activity, develop in all tokamaks and have traditionally been seen as independent of each other.

Surprise clue

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