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Twisted field
Helical coils wrap a torus so field lines never close on themselves the wrong way.
Magnetic confinement
Twist the doughnut until the magnets do all the steering. No giant plasma current required. Harder to build. Built to run steady — more like a furnace than a pulse.
The twist is the invention. Lyman Spitzer, 1951. Optimized in silicon, then in steel.
How it works
A tokamak uses plasma current to twist the field. A stellarator twists the coils instead. That is why the 3D looks knotted — the knot is the confinement.
Helical coils wrap a torus so field lines never close on themselves the wrong way.
No need to pulse a huge solenoid. Attractive if you want baseload, not bursts.
Type One Energy and Thea Energy are the American commercial stellarator companies — DOE milestone program included.
U.S. companies
Knoxville / Bull Run, Tennessee, and a PPPL spinout from Princeton.