Fusion advances with innovative stellarator research

Fusion advances with innovative stellarator research
by Clarence Oxford
Los Angeles CA (SPX) Dec 13, 2024

Plasma many times hotter than the sun's surface swirls inside a large metallic device designed to replicate the power source of stars: fusion. While the exterior resembles a metal ring surrounded by scaffolding, inside lies the cutting-edge technology aiming to achieve controlled fusion. Researchers supported by the Department of Energy's (DOE) Office of Science are making strides toward improving our understanding of fusion, with a particular focus on stellarators, a promising fusion device being studied at DOE's Princeton Plasma Physics Laboratory (PPPL).

Fusion, a potential clean energy source, produces no greenhouse gases or long-lived radioactive waste. It involves heating light elements like hydrogen to create plasma, a hot, charged gas comprising 99% of the visible universe. However, to generate energy sustainably, plasma must be controlled to maintain fusion reactions efficiently without constant energy input.

Magnetic confinement is one of the primary technologies researchers are exploring, with tokamaks and stellarators representing two leading configurations. Both utilize powerful magnetic fields to shape and confine plasma in a donut-like structure, but their methodologies differ significantly.

Tokamaks employ three major magnetic coil sets, with one generating a central electric current within the plasma to enhance magnetic confinement. Stellarators, on the other hand, use numerous external magnetic coils that create twisted fields around the plasma, eliminating the need for a central current. This unique design makes stellarators more flexible, less power-intensive, and less prone to plasma disruptions that could damage the device.

Despite these advantages, stellarators face a critical challenge: they struggle to confine the plasma's most energetic particles, essential for sustaining fusion reactions. Loss of these particles can damage the device walls and undermine efficiency. Tokamaks' symmetrical axis-based design naturally confines particles more effectively, highlighting a key hurdle for stellarators to overcome.

Researchers at PPPL have identified magnetic field configurations that improve confinement by influencing the behavior of trapped particles. To optimize these configurations, scientists would ideally simulate particle movement in every possible magnetic field. However, such simulations require impractical levels of computing power and time.

Instead, a collaborative effort involving PPPL, Auburn University, Germany's Max Planck Institute for Plasma Physics, and the University of Wisconsin-Madison employed an alternative approach. By developing a computationally efficient proxy function, the team predicted particle loss rates based on their movement relative to the magnetic fields. This proxy provided a reliable measure of confinement effectiveness, enabling the team to propose plasma configurations that minimize energetic particle losses.

Although this approach had been used for other stellarator models, it was the first application to this specific type. The team utilized advanced computational codes developed by DOE's Oak Ridge National Laboratory and PPPL to achieve their results.

While the proposed configurations are not yet tailored for a specific device, they offer a clear direction for future research. This innovative method represents a significant step toward making stellarators a practical option for commercial fusion energy production.