Stellarator
A machine that confines plasma using only the magnetic field of intricately twisted coils. Unlike a tokamak, it does not need a large current flowing through the plasma.
Lyman Spitzer at Princeton conceived it around 1951 and published the concept in 1958[1]. The name comes from the Latin stella, star — the aim was to reproduce the energy source of the stars on Earth.
Where a tokamak twists its field lines with a current in the plasma, a stellarator twists them with the shape of the coils themselves. Without a plasma current it is, in principle, suited to continuous operation and far less prone to disruptions.
The price is coils with complicated three-dimensional shapes that are hard to design and build. In the late 1960s the tokamak overtook it in performance, and the stellarator lost its place as the main line.
Its comeback came once computers could optimise the magnetic geometry: Germany's Wendelstein 7-X made its first plasma in 2015[2].
Related terms
- TokamakA doughnut-shaped machine that confines plasma by combining the magnetic field of external coils with the field produced by a current driven through the plasma itself. The dominant approach to magnetic confinement.
- Magnetic confinementHolding a hot plasma away from the vessel walls in a cage of magnetic field, using the fact that charged particles spiral along magnetic field lines.
- Lawson criterionThe condition that a plasma's density, confinement time and temperature must meet for a fusion reactor to produce net energy, derived by John Lawson in Britain in 1955.