Research published in Physical Review Letters demonstrates that an initial measurement of magnetic island ion temperature has displayed a steep gradient, offering insights into enhancing tokamak plasma confinement.
Image Credit: Bardoczi, L., et al., Perturbed Ion Temperature and Toroidal Flow Profile Measurements in Rotating Neoclassical Tearing Mode Magnetic Islands. Physical Review Letters 132, 065107 (2024).
Fusion power plants in the future will need adequate plasma confinement to generate energy and maintain reactions. A tokamak device contains plasma for fusion reactions, applying magnetic fields to "bottle" plasma. Magnetic islands, however, are instabilities in plasma and can demolish the confining magnetic field if they become big enough.
Researchers think islands become larger due to electron and ion temperatures in a plasma flattening out inside the island. Despite observation of this flattening, researchers have yet to measure island ion temperatures. At the DIII-D National Fusion Facility, researchers discovered that the ion temperature profile displayed a steep alteration across islands despite the flattened electron temperature profile.
The Impact
Adequate confinement of a stable plasma is needed for fusion energy production. This study offers an understanding of how islands have an impact on plasma stability. Scientists predict finding islands big enough to lead to loss of confinement in tokamak devices, including ITER, the global experiment now being prepared in France, as well as future fusion power plants.
They require accurate prediction and modeling of island destabilization to enable scientists to later create operating conditions enabling fusion devices to avoid islands and assist in enhancing plasma modeling and future device design.
Summary
Magnetic islands are plasma instabilities that can become larger and cause confinement loss and a sudden burst of energy that can harm a tokamak's internal wall. The electron temperature profile flattens inside islands, supporting island growth. However, ion temperature has yet to be measured inside an island.
Research undertaken at the DIII-D National Fusion Facility on the tokamak displays this parameter's first measurement, and its results demonstrate that ion temperature has a steep gradient in the middle of magnetic islands.
A global team of scientists carried out a series of simulations to understand this gradient. Reducing Drift-Kinectic Neoclassical Tearing Mode simulations explained this steep ion temperature shift. The scientists discovered that ions form "drift island" structures within islands, moving from them and restoring ion temperature.
The findings will be utilized within a physical model of island destabilization, assisting in the constraint of the Drift-Kinetic magnetic island onset model and offering fundamental data for fusion power plant design and ITER.
Funding
The Department of Energy (DOE) Office of Science, along with the Office of Fusion Energy Sciences, utilizing the DIII- National FusionFacility, a DOE Office of Science user facility, supported this study.
The simulations carried out at York Plasma Institute were conducted within the EUROfusion Consortium framework, with funding produced by the Euratom Research and Training Programme in the European Union.
Journal Reference:
Serdar, E. et. al. (2024) Wavefunction matching for solving quantum many-body problems. Nature. doi.org/10.1038/s41586-024-07422-z