Fusion is the sun’s energy source. It is essentially inexhaustible, and that’s a major reason for the interest in developing fusion technology to generate power. In the sun, light nuclei such as hydrogen, under extreme gravitational pressure and excited by temperatures of 10 million to 20 million°C, collide with such force that they are fused into heavier ones. The fusion generates heat, maintaining the high temperature and keeping the reaction going.

Photo: Agence Iter France

Fusion in earth’s lower pressure requires a much higher temperature of 100 million°C. Instead of hydrogen, its fuel is deuterium and tritium, heavy isotopes of hydrogen. To maintain the necessary high temperature, it confines the reaction with a magnetic field surrounding the plasma, in which the reaction is occurring. Magnetic-field confinement prevents the hot plasma from touching the torus wall, which would cool the plasma and inhibit the reaction.

Deuterium is readily extractable from ordinary water; tritium can be produced from lithium, also widely available. Unlike a fission reaction, the fusion reaction cannot get out of control because the plasma cools and halts the reaction if it touches the vessel’s wall. Environmental impacts are minimal because there are no air emissions, and tritium, produced in small quantities, has a short half-life and low radioactivity. The byproducts of fusion are not suitable for production of nuclear weapons.

Fusion’s promise of limitless energy from widely available fuel and negligible environmental impacts has kept interest in the technology high for more than 40 years.