A research team has presented a method to reduce the damage of runaway electrons in tokamak fusion devices. This strategy utilizes Alfvén waves to disrupt the harmful electron discharge cycle. This discovery marks an advance in fusion energy, with potential implications for the ongoing ITER project in France.
Researchers have used Alfvén waves to attenuate runaway electrons in tokamak fusion devices, having major implications for future fusion energy projects, including ITER in France.
Scientists led by Zhang Liu of the Princeton Plasma Physics Laboratory (PPPL) revealed a promising approach to reduce the damage of runaway electrons caused by turbulence in tokamak fusion devices. The key to this approach is utilizing a unique genre of plasma waves named after astrophysicist Hans Alvén, who won the Nobel Prize in 1970.
Alfvén waves have long been known to loosen the restraints of high-energy particles in tokamak reactors, allowing some particles to escape and reducing the efficiency of the donut-shaped devices. However, new findings by Zhang Liu and researchers at General Atomics, Columbia University, and PPPL have revealed useful results in the case of runaway electrons.
A great circular process
The scientists found that the loosening could scatter or dissipate high-energy electrons before they turned into avalanches that damaged the tokamak’s components. This process is determined to be highly circular: the runaways create instability that gives rise to Alfvén waves that prevent avalanches from forming.
“These findings provide a comprehensive explanation of the direct observation of Alfvén waves in inactivation experiments,” said Liu, a researcher at PPPL and lead author of the paper detailing the findings. Physical review letter. “The results show a clear connection between these patterns and the generation of runaway electrons.”
Chang Liu. Credit: Elle Starkman
The researchers deduced a theory for the observed set of interactions. The results matched those of escapees in experiments conducted at National Fusion Facility DIII-D, a Department of Energy tokamak operated by General Atomics for the Office of Science. Testing of the theory also proved positive on the Summit supercomputer located at Oak Ridge National Laboratory.
“Zhang Liu’s work shows that the size of the loose electron pool can be controlled by the instability driven by the loose electrons themselves,” said Felix Parra Diaz, Head of Theory at PPPL. “The research is particularly exciting because it could lead to tokamak designs that naturally reduce runaway electron damage through inherent instability.”
Thermal cooling
Turbulence begins with a sharp drop in temperature of millions of degrees required for fusion reactions. This subsidence, called “thermal cooling,” releases avalanches of landslides similar to landslides triggered by earthquakes. “Controlling turbulence is a big challenge for the success of tokamaks,” Liu said.
Fusion reactions combine light elements in the form of plasma – hot, charged matter consisting of free electrons and atomic nuclei called ions – to release enormous energy that powers the sun and stars. Reducing the risk of turbulence and electron escape would provide unique benefits to tokamak facilities designed to reproduce such processes.
Reducing the risk of turbulence and electron escape would provide unique benefits to tokamak facilities designed to reproduce such processes.
Nuclear fusion energy can be an important sustainable energy source to complement renewable energy sources. The world’s largest fusion experiment, ITER, is now being built in France. Credit: ITER
This new approach could impact the progress of the ITER project, an international tokamak being built in France to demonstrate the practical application of fusion energy and could represent a major step in the development of fusion power plants.
“Our findings pave the way for creating new strategies to mitigate loose electrons,” Liu said. Currently in the planning stages there is an experimental campaign in which the three research centers aim to further develop the amazing results.
2023-10-02 04:36:45
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