High-temperature physics is concerned with the production and analysis of the effects of temperatures above about e 50,000°C (90,000°F). At such temperatures atoms begin to be ionized (stripped of their electrons) and a fourth state of matter, called plasma, is achieved. Normal stars are plasma; so is the matter at the heart of an exploding hydrogen bomb. To make controlled thermonuclear fusion (joining of light nuclei and release of energy) a reality, physicists must find a way to confine a plasma at temperatures of over a million degrees.