Physicists at the U.S. Department of Energy (DOE) Princeton Plasma Physics Laboratory (PPPL) have proposed the source of the sudden and puzzling collapse of heat that precedes disturbances that could damage donut-shaped tokamak fusion facilities. By managing the resource, one of the most critical challenges that future fusion plants will face could be addressed and the production on Earth of the fusion energy that powers the sun and stars could be brought closer to Earth. bring reality.
Researchers traced the collapse to the 3-D disorder of the strong magnetic fields that bottled up the hot, charged plasma gas fueling the reactions. “We have proposed a new way to [disordered] field lines, which were mostly ignored or poorly modeled in the previous studies,” said Min-Gu Yoo, a postdoctoral researcher at PPPL and lead author of a Physics of plasmas paper selected as the editor’s choice along with a figure on the cover of the July issue. Yoo has since become a staff scientist at General Atomics in San Diego.
The strong magnetic fields in fusion facilities replace the immense gravity that holds fusion reactions in place in celestial bodies. But when disrupted by plasma instability in lab experiments, the field lines allow the superhot plasma heat to quickly escape the confinement. Such million-degree heat crushes plasma particles together to release fusion energy and can hit and damage the walls of the fusion facility when released from confinement.
“In the event of a major disturbance, field lines become total” [disordered] like spaghetti and connect quickly to the wall of very different lengths,” said lead research physicist Weixing Wang, Yoo’s PPPL advisor and a co-author of the paper. “That puts tremendous plasma thermal energy against the wall.”
Fusion combines light elements in the form of plasma – the hot, charged state of matter made up of free electrons and atomic nuclei – generating enormous amounts of energy. Plasma contains free electrons and atomic nuclei, or ions, and comprises 99% of the visible universe. Scientists around the world are trying to capture and master the fusion process on Earth to create a clean, carbon-free and virtually inexhaustible source of energy to generate electricity.
Hills and valleys
What was previously unknown was the 3D shape, or topology, of the tangled field lines caused by turbulent instability. The topology forms small hills and valleys, Yoo explains, with some particles remaining in valleys and unable to escape confinement, while others roll down the hills and hit the facility walls.
“The existence of these mounds is responsible for the rapid temperature collapse, called thermal quench, as they allow more particles to escape to the tokamak wall,” Yoo said. “What we showed in the article is how to draw a good map to understand the topology of the field lines. Without magnetic hills, most electrons would be trapped and would not be able to produce the thermal extinction observed in experiments.” .”
PPPL scientists simulated the thermal quench topology as a complex 3D structure rather than a simple 1D structure as depicted. In doing so, the researchers avoided common oversimplifications that could mislead physics.
What made the topology difficult to understand was the complex interaction between the electric and magnetic fields in the facility, Yoo said. PPPL researchers have unraveled the interaction using the lab’s GTS code, which simulates the effect of turbulent instability on particle motion. The code revealed that the electric field produced in facilities kicks particles between spaghetti-like stochastic magnetic field lines and then facilitates the movement of trapped particles along the field lines giving rise to the thermal extinction.
“This research provides new physical insights into how the plasma loses its energy to the wall when there are open magnetic field lines,” Yoo said. “The new understanding would be helpful in finding innovative ways to reduce or prevent thermal quenching and plasma perturbations in the future.”
Upgraded Code Reveals a Source of Malicious Fusion Disruptions
Min-Gu Yoo et al, The 3D magnetic topology and plasma dynamics in open stochastic magnetic field lines, Physics of plasmas (2022). DOI: 10.1063/5.0085304
Quote: Scientists bring the fusion energy that illuminates the sun and stars closer to reality on Earth (2022, September 27) retrieved September 27, 2022 from https://phys.org/news/2022-09-scientists-fusion- energy-sun-stars.html
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