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"AND""OR"

Fusion
A fusion reaction is one in which two atomic nuclei merge to form a heavier nucleus. This is the process that happens in the stars. In average stars, like the sun, the process of fusion is converting hydrogen nuclei (or protons) into helium nuclei. There is an enormous amount of kinetic energy and gamma rays released in this process that heat the star's interior, and this release is what maintains it at the extremely high temperatures (greater than 10 million K) required to continue the fusion. This process which has been making the stars go for billions of years, has clear potential as a power source on earth. Once we have started the reaction, fusion requires no energy and releases energy in a great surplus. It also has no environmental problems and causes no pollution whatsoever. The problems with fusion are the molecules of hydrogen, that are supposed to be fused, electro-statically repel each other at a great force. The only way to create the conditions where it is possible to force these atoms together and override their repulsion is through enormous heat, this method is called thermonuclear. Even though fusion research still needs a lot of time, there has been some progress in discovering how we can use this. The two fusion reactions that are the most promising, both involve the heavier isotopes of hydrogen: 1) deuterium (composed of one proton and one neutron) Deuterium occurs naturally as a minor constituent in all hydrogen-containing materials--such as water--in quantities sufficient to meet all the energy needs of societies for many billions of years. 2) tritium (composed of one proton and two neutrons). Tritium can be bred from lithium by a neutron-induced reaction in a blanket that could conceivably surround a fusion reactor. The western United States contains large lithium deposits in the salts of dry lake beds, and much larger quantities are dissolved in the sea. Scientists are trying different combinations of these nuclei to make fusion. The reaction that occurs with the greatest probability and at the lowest temperatures involves the fusing of a deuterium nucleus with a tritium nucleus to form a helium (He4) nucleus and a neutron. The products contain 17.6 million electron volts of released kinetic energy, this is great--except it's only in theory. At this time, the problem facing scientists is how to get the deuterium nucleus and the tritium nucleus to fuse. The other objective is to create an energy source that can get more energy out than is put in. The first method tried was to use a charged particle accelerator to bombard a solid or gaseous tritium target with energetic deuterium nuclei. This technique consumes power rather than producing it, however, because most of the accelerated nuclei lose their energy traveling at this speed. Another idea proposed in 1990 involved Tritium within metal bars that was put into a tank of deuterium in water. When energy was put into this tank something in the tritium bars forced deuterium out of the water and a chemical reaction fused the materials. Unfortunately, that was again a net energy loss, and only a small amount of extra heat was produced. Another approach to fusion, pursued since about 1974, is termedinertial confinement. Its aim is to compress a solid pellet of frozen deuterium and tritium to very high temperatures and densities in a process analogous to what occurs in a thermonuclear (hydrogen) bomb. The compression is accomplished by bombarding the pellet from all sides, simultaneously, with an intense pulse of LASER light, ions, or electrons. In 1988 it was learned that the U.S. government, which secretly had been using underground nuclear tests in Nevada to study inertial -confinement fusion, had achieved such fusion in 1986 by this means, unfortunately it only lasted less than a second. After trying these methods, most scientists now agree that the only way there is a net energy gain obtained is by mimicking the Sun, and producing starlike thermonuclear conditions. The goal of fusion--in effect, to make and hold a small star--is so daunting as to be widely considered the supreme technological challenge yet undertaken. In addition to an almost inexhaustible fuel supply, fusion has other attractive features: it is environmentally benign; the resulting ash is harmless helium and hydrogen; and the afterheat in the reactor structure would be much less than in a fission reactor and would be distributed through a greater thermal mass. In addition, because fusion is not a chain reaction, it cannot run out of control, and any tampering to the process would cause the plasma (the energy involved in the process) to extinguish itself. It would also be far more difficult to produce nuclear-weapons materials surreptitiously at a fusion plant than at a fission plant; because no fissionable material should ordinarily be present at a fusion plant. Present levels of support for research are aimed at building the first demonstration fusion plant in about the year 2024. This year is based on the amount necessary for fusion research and the very small amount of money given to fusion to this research by most governments.

 



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