Word: fusion
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These conditions exist, more or less, in the sun and other stars, where the tremendous gravitational forces of the giant bodies, combined with their huge amounts of hydrogen, produce self-sustaining fusion reactions. But producing controlled fusion on earth is a far more difficult task-and to do it practically and economically may well be the most complicated technological venture ever attempted. Says Physicist Gerald Yonas of New Mexico's Sandia Laboratories, a federally supported atomic research facility: "It's the most exciting area today in science. Fusion power is a mountain we have to climb...
...first steps on that ascent was the realization that the conditions of temperature and density necessary for the sustained fusion of ordinary hydrogen nuclei were far beyond the present capabilities of science. But experiments showed that it was easier to fuse two isotopes, or different forms, of hydrogen: deuterium and tritium. Reason: the nuclei of these isotopes have larger cross sections than those of ordinary hydrogen nuclei. Thus the probability of direct collisions between them is increased and that in turn means that less extreme conditions are required to make them fuse. The easiest fusion to attain, scientists determined...
Tiny Bombs. Still, to join enough deuterium and tritium nuclei to sustain a fusion reaction requires heroic efforts. Deuterium-tritium gas mixtures must be heated to as much as 100 million degrees Celsius and be maintained at that temperature for about one second at a density of about 1014 (100 trillion) particles per cubic centimeter. Scientists have taken two different routes in their efforts to achieve these critical conditions. One is to use a "magnetic bottle" -an enclosing magnetic field-to contain the hydrogen fuel. The other is to use lasers or electron beams to make miniature hydrogen "bombs...
...thus becomes a "plasma"-a mixture of negatively charged electrons and positively charged nuclei, or ions. Because these charged particles will not generally cross magnetic lines of force, they can be confined by a powerful magnetic field. The magnetic bottle is the only known practical container in which fusion can be sustained for any significant amount of time. If a plasma were to come in contact with the walls of a reactor, it would pick up impurities, lose energy and suffer a temperature drop that would immediately halt any fusion reaction...
Ectoplasmic Bagel. The magnetic containment devices most widely used in fusion experiments are called "tokamaks." Invented by Soviet scientists in the early 1960s, tokamaks are toruses, or doughnut-shaped chambers, surrounded by huge electromagnets. Gas is fed into the chamber and heated until it becomes a plasma. Powerful fields produced by the magnets hold the plasma and keep it from touching the chamber walls. The temperature of the plasma is raised closer to fusion temperatures by passing electric currents and shooting beams of high-energy atoms through it. With these techniques, tokamaks have come the closest of any magnetic device...