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Question
How do you confine something that hot?
You don't touch it — you hold it in a magnetic field. A fusion plasma is confined by magnetic forces, never in contact with any material wall.
The answer to "how do you hold something that hot" is the founding idea of the whole field: magnetic confinement. The wall's job is handled separately by the divertor and plasma-facing components.
Questions & answers
How can anything hold a hundred-million-degree plasma?
Nothing material could — so nothing material touches it. Because the plasma is electrically charged, its particles are trapped along magnetic field lines. A carefully shaped magnetic field forms an invisible bottle that suspends the plasma in a vacuum, away from every surface.
What about the wall — doesn't it get destroyed?
The wall never sees the core temperature. It handles a manageable heat and particle flux at the plasma edge, concentrated at the divertor, which is engineered to take it. The Kronos first wall uses laser-fused hafnium carbide, and the low-neutron fuel means far less material damage than a D–T plant.
Is magnetic confinement the only way?
No — inertial confinement compresses a fuel pellet with lasers instead. Kronos uses magnetic confinement, which suits a steady, continuously-running power plant.