stellarators

A stellarator is a type of magnetic confinement fusion device that uses external magnetic coils to generate a twisted, three-dimensional magnetic field in which hot plasma can be confined without relying on a large current in the plasma itself. The term reflects the star-like nature of the magnetic field geometry that traps particles along complex field lines.

Operation relies on a carefully arranged set of external coils around a toroidal chamber. The coils produce helical or non-axisymmetric magnetic fields, creating magnetic surfaces that wind around the torus. This external-field confinement aims to hold high-temperature plasma long enough for fusion reactions to occur, potentially enabling steady-state operation.

Compared with tokamaks, stellarators confine plasma primarily with external magnets rather than a large toroidal current. This reduces the risk of current-driven instabilities and disruptions and supports continuous operation. However, the coil geometry is highly intricate, making design, manufacturing, and precise construction challenging. Achieving good confinement also depends on optimizing the magnetic field symmetry to minimize neoclassical transport.

Historically, stellarators emerged from Lyman Spitzer’s ideas in the mid-20th century. Modern devices include the Large Helical Device (LHD) in Japan, the Wendelstein 7-X in Germany, and the Helically Symmetric eXperiment (HSX) in the United States. These projects pursue long-pulse or steady-state operation and aim to demonstrate favorable confinement in non-axisymmetric fields.

Stellarators remain a major research path in magnetic confinement fusion. They offer potential advantages for continuous fusion power with reduced disruption risk, but require advances in coil design, fabrication precision, and plasma control to achieve practical reactors.