stellarator

A stellarator is a type of magnetic confinement fusion device that uses externally generated magnetic fields to confine hot plasma in a toroidal shape. The goal is to maintain the conditions necessary for fusion reactions without relying on strong plasma currents, which can drive instabilities in other confinement concepts. In a stellarator, the magnetic field lines wind around the torus in three dimensions, forming twisted, helical paths that help trap charged particles and reduce transport losses.

The confinement is achieved with a complex arrangement of non-axisymmetric coils positioned around the vacuum chamber. The geometry is designed to produce a three-dimensional magnetic field that approximates quasi-symmetric or quasi-helical properties, minimizing neoclassical transport and improving stability. This coil design allows potential steady-state operation, but it also presents significant engineering challenges due to the intricate shapes and precise alignment required.

Historically, early stellarators faced difficulties with poor confinement and engineering complexity. Advances in computer optimization and coil fabrication led to modern devices such as the Wendelstein 7-X in Germany, which uses a sophisticated modular coil system and optimized magnetic fields to study improved confinement and stability in a quasi-isodynamic configuration.

Stellarators remain an active area of fusion research, contributing data on magnetic field behavior, plasma transport, and edge and divertor physics. They are studied alongside tokamaks and other confinement concepts to evaluate approaches for steady-state fusion and to inform the development of future reactors.