Fusion Friday (3): Introduction to ITER Magnets

The International Thermonuclear Experimental Reactor (ITER) uses the technique of “magnetic confinement” to contain the hot plasma in which the fusion reactions occur and to deliver the energy that heats the plasma to ignition temperature. These magnets are gargantuan by every measurement. The central solenoid magnet weighs 1000 tonnes and stands 13 metres tall and 4.3 metres wide and generates a magnetic of field of 13 teslas from a current of 45 kiloamperes. The toroidal field coils, 18 in all, store a total energy of 41 gigajoules, equivalent to around 9 tonnes of TNT. When operating, the magnets exert a force of 50,000 tonnes on the structure and a compressive force of 40,000 tonnes toward the centre. The superconducting niobium-tin coils must be kept at a temperature around 4° K lest they quench and release all of that energy in an instant. And they operate in close proximity to a plasma at a temperature in excess of 150 million degrees Kelvin.

This is difficult.