Hot Fusion Heats Up as Hot News Topic
Six months ago, there was considerable excitement when two scientists claimed they had developed a method of cold fusion--the production of energy by causing small atomic nuclei, at room temperature, to join together (“fuse”) into larger ones. If they were right, the process would provide a cheap source of unlimited energy. But the furor faded quickly once it seemed the original report was mistaken.
However, attempts at hot fusion, which have been going on for nearly 40 years, have not stopped. And just last month a new and promising way of achieving it was announced.
In the two places where we know that fusion takes place--the center of stars (including our sun), and in an exploding hydrogen bomb--atomic nuclei are forced together under conditions of very high energy, making use of enormous temperatures or pressures or both.
Scientists are trying to bring about controlled hot fusion, making it take place in the laboratory at a rate that does not produce an explosion but rather a slow and steady energy output, greater than that required to start the fusion. This energy can then be made to do the same useful work as, say, energy from a hydroelectric dam or coal-fired power plant. And if heavy hydrogen is used as the fuel, enough fusion energy can be produced at a reasonable rate to last humanity for billions of years (if humanity lasts that long).
There are two chief ways in which the production of such controlled fusion has been tried.
In the first way, the electrically charged nuclei of heavy hydrogen atoms and other fusible materials were heated to an extremely high temperature while they were held in place by a magnetic field.
This has been the most hopeful method, and very large and very expensive machines called tokamaks (first produced by the Soviet Union) have been used for the purpose. Scientists have slowly learned to produce higher and higher temperatures and to keep the heavy hydrogen magnetically in place for longer and longer intervals. They have come closer and closer to the goal of producing more energy than they expend--but they haven’t quite reached it yet.
In the second way, a little glob of frozen heavy hydrogen is hit from a number of directions by concentrated laser beams. The energy from these beams heat the hydrogen so rapidly (it is hoped) that fusion begins before the hydrogen can expand and vanish into the surrounding atmosphere. For the purpose, larger and more efficient lasers are built--but, again, scientists haven’t quite reached the goal of getting out more energy than they are putting in.
But Lewis Friedman heads a group at Brookhaven Laboratory in Long Island which, for five years, has been trying a third method. They begin with frozen pellets containing heavy hydrogen atoms. But, instead of bombarding it with laser beams, they bombard it with tiny clusters of other pellets containing heavy hydrogen. The two sets of pellets come together with great force, raising the temperature almost instantaneously to a hundred million degrees or more and producing fusion.
The stationary target contains heavy hydrogen atoms in combination with metals or as part of plastics. The bombarding pellets consist of ice that contains heavy hydrogen. The Brookhaven scientists report they have indeed produced fusion for they have been able to detect its products: nuclei of ordinary hydrogen (protons), of super-heavy hydrogen (tritium) and of helium. They are also looking for speeding neutrons of proper energy levels, which will be the best evidence of all.
So far the bombarding pellets are very small indeed. They contain anywhere from 25 to 1,300 molecules of frozen water, far too small to see with anything but the most advanced electron microscopes.
Just as in the other two ways of tackling controlled fusion, things must now be made larger and more powerful. Larger pellets must be produced, and they must be fired at the target with even greater speed and energy. Larger pellets would increase the number of hydrogen nuclei undergoing fusion. If these were speedier and more energetic, that would make them penetrate the target more deeply, and this also would increase the number of hydrogen nuclei undergoing fusion.
The Brookhaven group estimates that the amount of fusion produced by this method must reach a level at least a million times higher than has yet been reported before a “break-even” point is reached; that is, before the amount of energy produced is at least equal to the amount put in. Beyond that, they would begin to make an energy profit, and the possibility of a continuing production of useful energy would arise.
Nuclear fusion, if achieved, would be a plentiful source of energy that would not produce gases that cause pollution and the greenhouse effect, as the burning of coal and oil does. It may also produce far less radiation danger than ordinary nuclear fission does. Now we have a third possible way of reaching this desirable goal.
