A plain-language guide to the tokamak’s twisted cousin — a device that creates its confining magnetic field entirely with external coils, eliminating the need for plasma current and enabling true steady-state operation.
A tokamak needs a large electrical current flowing through the plasma itself to create part of the confining magnetic field. This current is driven by a transformer (the central solenoid), which can only operate in pulses — like a battery that must be periodically recharged. A stellarator solves this by creating the entire confining field with carefully shaped external coils, requiring no plasma current at all.[1]
A stellarator confines plasma in a toroidal (doughnut-shaped) vessel, just like a tokamak. The difference is in the magnetic field. Instead of relying on plasma current, a stellarator uses non-planar coils — coils that twist and bend in three dimensions — to create a magnetic field with the exact helical twist needed for confinement. The coils are extraordinarily complex to design and manufacture, but once built, the magnetic field is inherently steady-state.
Advantages: True steady-state operation (no pulsing), no disruptive instabilities (no plasma current to disrupt), intrinsically stable operation. Challenges: The 3D geometry makes the coils extremely expensive to manufacture (each coil is unique), and historically, particle confinement was worse than in tokamaks due to trapped-particle losses.[2]
Modern stellarators overcome the confinement problem through computational optimization. By carefully shaping the magnetic field to have specific symmetry properties (quasi-symmetry or quasi-isodynamicity), neoclassical losses can be reduced to tokamak levels. Wendelstein 7-X in Germany has proven this works experimentally. Multiple private companies (Type One Energy, Proxima Fusion, Thea Energy) are now pursuing optimized stellarators as the basis for commercial reactors.[3]