physicists at the Princeton Plasma Physics Laboratory (PPPL) of the U.S. Department of Energy (DOE) have hypothesised the cause of the abrupt and perplexing collapse of heat that occurs before disturbances that can harm doughnut-shaped tokamak fusion plants. Dealing with the source could help future fusion facilities overcome one of their biggest obstacles and move the generation of the fusion energy that powers the sun and stars on Earth closer to reality.
The powerful magnetic fields that contain the hot, charged plasma gas that powers the reactions were found to be 3D disordered, which is what caused the collapse, according to researchers. The lead author of a Physics of Plasmas paper that was chosen as an editor's pick and had a figure placed on the cover of the July issue, Min-Gu Yoo, a post-doctoral researcher at PPPL, said, "We proposed a novel way to understand the [disordered] field lines, which was usually ignored or poorly modelled in the previous studies. Yoo is currently a scientist on staff with General Atomics in San Diego.
In fusion facilities, powerful magnetic fields take the place of the intense gravity that holds fusion reactions in place in celestial bodies. However, in laboratory trials, when the plasma becomes unstable, the field lines allow the extremely high plasma heat to quickly escape containment. When liberated from confinement, this one million degrees of heat can impact and harm the walls of fusion facilities by crushing plasma particles together to release fusion energy.
Yoo's PPPL adviser and coauthor Weixing Wang noted that in the major disruption instance, field lines "become entirely [disordered] like spaghetti and link fast to the wall with extremely variable lengths." The wall is being hit by a tremendous amount of plasma thermal energy.
Light components are fused together in fusion to create plasma, a hot, charged state of matter made up of free electrons and atomic nuclei that produces enormous amounts of energy. 99% of the observable cosmos is made of plasma, which is composed of ions and free electrons. In order to develop a clean, carbon-free, and essentially limitless source of energy to generate electricity, scientists from all over the world are working to capture and regulate the fusion process on Earth.
Mountains and valleys
What wasn't previously recognised was the disorganised field lines' 3D shape, or topology, which is brought on by chaotic instability. According to Yoo, the topology creates tiny hills and valleys, some particles become stuck in the valleys and are unable to escape containment, while others roll down the hills and strike the facility's walls.
Because they allow more particles to escape to the tokamak wall, Yoo claimed that the hills' existence is to blame for the rapid temperature decrease, or "thermal quench." "In the paper, we demonstrated how to create a useful map for comprehending the topology of the field lines. Without magnetic hills, the majority of electrons would be confined and unable to cause the experimentally observed thermal quench."
The thermal quench topology was not modelled as a straightforward 1D structure, but rather as a sophisticated 3D structure by PPPL researchers. The researchers did this to steer clear of common oversimplifications that might lead to physics errors.
According to Yoo, the facility's complicated interaction of the electric and magnetic fields made it challenging to comprehend the topology. Using the Laboratory's GTS algorithm, which mimics the impact of turbulent instability on particle movement, PPPL researchers were able to decipher the connection. According to the code, the electric field created by buildings acts to propel particles along spaghetti-like stochastic magnetic field lines, which then makes it easier for trapped particles to move along the field lines and cause the thermal quench.
When there are open magnetic field lines, Yoo said, "this finding provides fresh physics insights into how the plasma loses its energy towards the wall." The new knowledge might be useful in developing cutting-edge strategies to lessen or prevent thermal quenches and plasma disturbances in the future.
Reference: Physics of Plasmas
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