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FusionBenchmark

Tokamak vs stellarator

Both confine plasma magnetically in a torus. The difference is where the twist in the magnetic field comes from — and everything else follows from that.

Tokamak

Doughnut-shaped magnetic confinement using a strong toroidal field plus a current driven through the plasma itself. The most-studied configuration, and the one ITER uses. Its main open problem is heat exhaust at the divertor, where the plasma edge concentrates power onto a small area, together with the risk of disruptions: sudden, uncontrolled losses of the plasma current.

54 devices · 13 organisations · 272 measurements

Stellarator

Confinement produced by external coils twisted into complex three-dimensional shapes, so no net current has to be driven through the plasma. That removes the disruptions a tokamak's plasma current can cause and allows continuous operation, at the price of coils that are far harder to design and build.

16 devices · 9 organisations · 46 measurements

Differences

Tokamak vs stellarator compared
  Tokamak Stellarator
Where the field twist comes from A current driven through the plasma itself. The shape of the external coils alone.
Consequence for operation The plasma current must be sustained, which historically meant pulsed operation and makes long steady-state discharges hard. No plasma current is needed, so steady-state operation is natural. This is the central advantage.
Disruptions A sudden loss of plasma current can dump the stored energy into the wall. Disruption mitigation is a major engineering programme. No large plasma current, so current-driven disruptions are largely absent.
Engineering difficulty Coils are comparatively simple and axisymmetric. Coils are three-dimensional and must be manufactured to very tight tolerance. This is why there are far fewer of them.
Maturity By far the most-built approach, and the basis of ITER. Fewer machines, but W7-X holds the stellarator record for triple product.

Devices

Tokamak 54

Stellarator 16

Organisations

Tokamak 13

Commonwealth Fusion SystemsEnergy SingularityFirefly FusionGeneral AtomicsInstitute of Plasma Physics, Chinese Academy of SciencesITER OrganizationKorea Institute of Fusion EnergyMaritime FusionMax Planck Institute for Plasma PhysicsMIT Plasma Science and Fusion CenterNational Nuclear Center of the Republic of KazakhstanPranos FusionUK Atomic Energy Authority

Stellarator 9

Gauss FusionHelical FusionMax Planck Institute for Plasma PhysicsNational Institute for Fusion ScienceProxima FusionRenaissance FusionStellarex EnergyThea EnergyType One Energy