19.9 nuclear fusion  light nuclei combine to give a more stable heavy nucleus plus possibly several neutrons, and energy is released. Used in hydrogen bombs. Powers the sun and stars. (H atoms fuse to form helium atoms and release intense energy.) Sustainable fusion reactions require temperatures of about 100 million o C. Exists as a plasma (not solid, liquid, or gas) Difficult to make positive nuclei fuse together.

Advantages of fusion  More easily available  Doesn’t cause pollution to mine it  Not easily made into bombs  Waste products are much less radio active and have shorter half lives  Releases 3-10 times the amount of energy as fission

magnetic fusion reactor  Figure 21.20: Plasma confinement in a tokamak reactor. Courtesy of Princeton Plasma Physics Laboratory.