New research at the Princeton Plasma Physics Laboratory (PPPL) has shown that the rotation of the plasma core is a key factor in how particles are distributed within a fusion reactor system.
The study shows why plasma particles hit some parts of the reactor more than others.
This finding allows computer simulations to match experimental results, providing a tool for designing integrated power plants.
In a tokamak, gravity holds the plasma in a donut shape. Some particles eventually escape this magnetic field and head towards the deflector, which acts as a discharge mechanism.
“There, the plasma particles hit the metal plates, cool and bounce back. (The returning atoms help fuel the fusion reaction.) “said PPPL in a press release.
“But experiments consistently show that far more particles hit the target of an internal indicator than an external one.”
Problems in modeling an asymmetrical thermal load
This uneven distribution remained unexplained because existing models could not replicate the degree of asymmetry seen in physical experiments.
Understanding this distribution is essential for engineering future fusion systems. It will help to know exactly where the vapor particles will sit to ensure that the compressor is able to control the temperature without sustaining structural damage.
“The main focus was on what is known as net drift within the device itself, the lateral movement of particles across the lines of gravity,” explained the press release.
However, computer simulations that included only this type of drift did not produce an unbiased test pattern, making it difficult to trust the simulations to guide the design of future drifting machines.
Integrating core rotation into predefined simulations
To solve this, a team led by Eric Emdee at PPPL used the SOLPS-ITER model code. They analyzed data from the DIII-D tokamak in California.
The researchers tested four different conditions to determine the cause of the particle patterns: models with and without drifts, and models with and without plasma circulation.
The simulations match the experimental data only when the group includes a measured rotation of 88.4 kilometers per second.
This toroidal circulation—the movement of particles around the tokamak—creates a uniform flow along the lines of gravity.
Emdee noted that although cross flow was considered the main driver of asymmetry, this study shows that the same flow driven by the rotating base is just as important.
“Many people say that the cross flow is what caused the asymmetry. What this paper shows is that the parallel flow, driven by the rotating base, is very important,” he emphasized.
Implications for future coalescence power plants
Research shows that the interaction between core rotation and field drift produces a greater effect than either component alone.
By accounting for how the rotating plasma impacts flow at the edge of the magnetic field, scientists can now predict the behavior of the exhaust more accurately.
This connection provides the information needed to design divertors that can withstand the heat of global fusion power generation.
“The finding suggests that accurately predicting the behavior of the meltdown in future fusion processes will require accounting for how the circulating plasma mixture influences blood flow, a connection that can help engineers design devices that can better handle reality,” concludes the press release.
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