Physicists at the US Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) have suggested the source of the sudden, baffling heat meltdown that precedes perturbations that could damage the bun-shaped tokamak fusion facilities. Dealing with the source could overcome one of the most important challenges for future fusion facilities and bring production on Earth closer to the fusion energy that drives the sun and stars.
The researchers traced the collapse to a 3-D perturbation of the strong magnetic fields that bathe the hot charges plasma gas feeds reactions. “We proposed a new way to understand [disordered] said Min-Jo Yu, a postdoctoral researcher at PPPL and lead author of Plasma physics The paper was selected as the Editor’s Choice with an image placed on the cover of the July issue. Yu has since become a staff scientist at General Atomics in San Diego.
The strong magnetic fields An alternative in fusion facilities to the massive gravity that keeps fusion reactions in place in celestial bodies. But when disturbed plasma Instability In laboratory experiments, superheat field lines allow plasmas to rapidly escape confinement. This million-degree heat smashes the plasma particles together to release fusion energy and can hit the walls of the fusion facility and damage them when released from confinement.
“In the event of a major disturbance, the entire field lines become [disordered] Like spaghetti and a wall speed dial of very different lengths, said lead research physicist Weixing Wang, Yoo PPPL consultant and co-author of the paper. “This brings enormous plasma Thermal energy against the wall.”
Fusion combines light elements in the form of plasma – the state of hot, charged matter that makes up it free electrons And the atomic nucleus – which generates huge amounts of energy. Plasma contains free electrons and atomic nuclei, or ions, and makes up 99% of the visible universe. Scientists all over the world are seeking to catch fusion An on-ground process to create a clean, carbon-neutral and virtually inexhaustible energy source for electricity generation.
Hills and valleys
What was not previously known was the three-dimensional shape, or topology, of the fuzzy field lines caused by the turbulent instabilities. Yu explains that the topology forms small hills and valleys, leaving some particles trapped in the valleys and unable to escape confinement while others roll down the hills and crash into the facility’s walls.
“The presence of these ridges is responsible for the rapid collapse in temperatures, the so-called thermal quenching, as they allow more particles to escape into the tokamak wall,” Yu said. “What we showed in the paper is how to draw a good map to understand the topology of the field lines. Without the magnetic ridge, most of the electrons would have been trapped and would not be able to produce the thermal cooling observed in the experiments.”
The PPPL scientists simulated the heat quenching topology as a complex 3D structure rather than a simple 1D structure as imaged. In doing so, the researchers avoid common oversimplifications that can mislead physics.
What made the structure difficult to understand, Yu said, was the complex interaction between electric and magnetic fields within the facility. The PPPL researchers revealed the interaction using the lab’s GTS code, which simulates the effect of turbulent instability on particle motion. The code revealed that a file electric field The product in the installations repels particles between random spaghetti-like magnetic field lines and then facilitates the movement of trapped particles along the field lines leading to thermal quenching.
“This research provides new physical insights into how the plasma loses its energy toward the wall when it is open magnetic field “The new understanding will be useful in finding innovative ways to mitigate or avoid thermal cooling and plasma disturbances in the future,” Yu said.
Min-Gu Yoo et al, Three-dimensional magnetic structure and plasma dynamics in open stochastic magnetic field lines, Plasma physics (2022). DOI: 10.1063/5.0085304
Princeton Plasma Physics Laboratory
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