The Foundations of Chemistry

a plasma.A very high temperature plasma is so hot that it melts and decomposes anything
it touches, including structural components of a reactor. The technological innovation
required to build a workable fusion reactor probably represents the greatest challenge ever
faced by the scientific and engineering community.
Recent attempts at the containment of lower temperature plasmas by external magnetic
fields have been successful, and they encourage our hopes. Fusion as a practical energy
source, however, lies far in the future at best. The biggest advantages of its use would be
that (1) the deuterium fuel can be found in virtually inexhaustible supply in the oceans;
and (2) fusion reactions would produce only radionuclides of very short half-life, primarily
tritium (t1/212.3 years), so there would be no long-term waste disposal problem. If
controlled fusion could be brought about, it could liberate us from dependence on uranium
and fossil fuels.

26-16 Nuclear Fusion 1033

Nuclear fusion provides the energy of our

sun and other stars. Development of

controlled fusion as a practical source of

energy requires methods to initiate and

contain the fusion process. Here a very

powerful laser beam has initiated a fusion

reaction in a 1-mm target capsule that

contained deuterium and tritium. In a 0.5-

picosecond burst, 10^13 neutrons were

produced by the reaction^21 H^31 H88n

4

2 He

1

0 n.

Plasmas have been called the fourth

state of matter.

The plasma in a fusion reactor must

not touch the walls of its vacuum

vessel, which would be vaporized.

In the Tokamak fusion test reactor,

the plasma is contained within a

magnetic field shaped like a

doughnut. The magnetic field is

generated by D-shaped coils around

the vacuum vessel.