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How does a tokamak work?
A tokamak confines fusion plasma in a magnetic bottle shaped like a doughnut, using a combination of external coils and a current in the plasma itself.
The tokamak is the most developed fusion device, and its core trick is the helical magnetic field. See tokamak, magnetic confinement, and flux surfaces for the physics, and what is a spherical tokamak? for the Kronos variant.
Questions & answers
How does a tokamak confine plasma?
A tokamak wraps the plasma in a doughnut-shaped magnetic field. External coils produce a field the 'long way' around the torus, while an electric current driven through the plasma adds a field the 'short way.' The two combine into helical field lines that particles spiral along — a magnetic bottle that keeps the hundred-million-degree plasma from touching any wall.
What holds the plasma in place?
The magnetic field. Because plasma is electrically charged, its particles are forced to follow field lines rather than fly straight. Additional shaping coils control the plasma's position and cross-section. Nothing physical touches the core.
What makes the Kronos tokamak different?
It's a compact, high-field spherical tokamak with a negative-triangularity shape and direct energy conversion — choices that let a small machine target gigawatt-class power on low-neutron fuel.