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| Groundbreaking Findings Pave the Way for Faster Attainment of Controlled Fusion Energy on Earth |
Researchers, led by Chang Liu from the Princeton Plasma Physics Laboratory (PPPL), have unveiled a promising method to tackle the issue of runaway electrons generated during disruptions in tokamak fusion devices. This breakthrough approach revolves around harnessing a unique type of plasma wave named after astrophysicist Hannes Alfvén, a Nobel laureate in 1970.
Alfvén waves have long been known to impact the confinement of high-energy particles in tokamak reactors, allowing some to escape and thereby reducing the efficiency of these doughnut-shaped devices. However, Liu and a team of researchers from General Atomics, Columbia University, and PPPL have discovered that Alfvén waves can have a beneficial effect when it comes to managing runaway electrons.
Remarkably, the scientists found that the loosening effect caused by Alfvén waves can scatter high-energy electrons before they develop into avalanches that could damage tokamak components. This process forms a circular chain reaction: runaway electrons trigger instabilities that, in turn, generate Alfvén waves, preventing the formation of avalanches.
Chang Liu, a staff researcher at PPPL and the lead author of a paper detailing these findings in Physical Review Letters, stated, "These discoveries provide a comprehensive explanation for the direct observation of Alfvén waves in disruption experiments. The findings establish a distinct link between these modes and the generation of runaway electrons."
Researchers have also developed a theory to explain the circularity of these interactions, and experimental results from the DIII-D National Fusion Facility, operated by General Atomics for the Department of Energy, have confirmed the validity of the theory. Furthermore, tests on the Summit supercomputer at Oak Ridge National Laboratory have yielded positive results.
Felix Parra Diaz, head of the Theory Department at PPPL, praised Chang Liu's work, stating, "Chang Liu's work shows that the runaway electron population size can be controlled by instabilities driven by the runaway electrons themselves. His research is very exciting because it might lead to tokamak designs that naturally mitigate runaway electron damage through inherent instabilities."
Disruptions in fusion reactions typically start with sharp drops in the million-degree temperatures required for these reactions to occur, known as "thermal quenches." These drops release avalanches of runaway electrons, similar to landslides triggered by earthquakes. Controlling disruptions is a significant challenge in achieving success with tokamak fusion devices.
Fusion reactions involve combining light elements in plasma form, which is the hot, charged state of matter composed of free electrons and atomic nuclei called ions. By mitigating the risk of disruptions and runaway electrons, the new approach offers significant benefits to tokamak facilities aimed at replicating fusion processes.
This breakthrough could have far-reaching implications for ITER, the international tokamak currently under construction in France, which aims to demonstrate the practicality of fusion energy. It could also mark a crucial step forward in the development of fusion power plants.
Chang Liu expressed optimism about the future, stating, "Our findings set the stage for creating fresh strategies to mitigate runaway electrons." The research centers involved are currently in the planning stage for experimental campaigns to further explore and develop these groundbreaking findings.
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