Magnetic fields are good at containing the searingly hot plasmas needed to make nuclear fusion work (see main story) - but not that good. Uncharged neutrons made in fusion reactions still leak out and hit the "first wall" closest to the nuclear reaction, causing radiation damage that means replacing this wall regularly. ITER, the biggest attempt at a fusion reactor yet currently under construction in the south of France, will have a reactor vessel bounded by 440 removable panels weighing 4 tonnes each, and an elaborate robotic system for handling them. Inertial confinement is a different approach. It relies on zapping fuel pellets with high-power lasers, compressing the resulting plasma and heating it so quickly that fusion occurs before it can fly apart. This is the method used by the US National Ignition Facility in Livermore, California, which opened for business in 2009. Its main focus is working out what happens within nuclear weapons rather than power generation, but others have taken the principle and aim to use it for commercial purposes.
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