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Magnetic bottle
Eighteen D-shaped coils (on SPARC) make a torus of field. Plasma is ionized, so it follows the lines.
Magnetic confinement
A doughnut-shaped magnetic bottle. Charged particles follow field lines and never touch the wall. It is the most studied fusion device on Earth — and the architecture behind SPARC in Fort Devens.
Drag to orbit. Plasma is pink — hydrogen Balmer-alpha. Magnets are steel. Field overlays are a diagram.
How it works
Toroidal-field magnets squeeze the plasma into a ring. Poloidal coils and a central solenoid drive and shape current. High-temperature superconductors let the whole machine shrink.
Eighteen D-shaped coils (on SPARC) make a torus of field. Plasma is ionized, so it follows the lines.
Stronger field, smaller machine. Fusion power in a tokamak scales steeply with B. That is why tape became a factory.
SPARC is the proof. ARC is the plant: neutrons heat a blanket, steam spins a turbine, ~400 MW.
U.S. companies
The U.S. commercial tokamak story, right now, is CFS in Devens — SPARC, then ARC in Virginia.