The Great Nuclear Fusion Race

Energy in limitless supply from a universally available fuel. Energy created by a process that is relatively harmless to the environment and leaves behind no byproduct that can be converted into dangerous weapons. To a world facing the long, frigid night of fuel shortages, it seems like a glorious dream. That dream may be somewhat closer to reality than most people realize. In laboratories in the U.S., the Soviet Union, Western Europe and Japan, scientists are involved in a spirited competition to become the first to achieve one of the most important--and difficult--goals ever sought by man: the harnessing of nuclear fusion. If that goal is reached, the world may never again be faced with an energy crisis.

Invisible Springs. Compared with the difficulties of controlling fusion, producing energy from nuclear fission is relatively simple. In fission--which occurs in A-bomb explosions and powers today's nuclear plants--a speeding neutron is used to split the atomic nucleus of a heavy element like uranium into the nuclei of one or more lighter elements. In the process, more neutrons are given off. But the mass of the resulting nuclei and neutrons is somewhat less than the mass of the original nucleus; the missing matter--as predicted by the famed Einstein equation E=mc2--has been converted into energy. Basically, all that is required for fission is the bringing together of enough uranium or plutonium in the right proportions.

In nuclear fusion--the process that feeds the fires of the sun and gives the H-bomb its awesome power--atomic nuclei of light elements like hydrogen collide and merge. The resulting nuclear particles contain less mass than the sum of the original nuclei; again, matter has been converted into energy. But while atomic nuclei easily split, they do not easily fuse; they have positive electric charges and thus repel each other, acting as if they had invisible springs between them. Getting them to join requires that they approach each other with enough energy to overcome their natural repulsion and smash together. Thus causing large numbers of nuclei to fuse and provide substantial energy requires three conditions: 1) very high temperatures (which impart great velocity to the nuclei), 2) high density (the nuclei crowded together to increase the probability of head-on collisions), and 3) confinement of the high-speed, densely packed nuclei for a long enough time to enable the fusion reaction to occur and to sustain itself.

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."

One of the 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, was between a deuterium and a tritium nucleus; they combine to form a helium nucleus and release energy in the form of a high-velocity neutron. Both isotopes are easily obtained. Each gallon of sea water contains one-eighth gram (.004 oz.) of deuterium, which can be converted into the energy equivalent of more than 1,100 liters (300 gal.) of gasoline. Tritium does not exist freely in nature but can be produced by bombarding lithium (which can be extracted in large quantities from rocks or sea water) with neutrons.

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" out of tiny pellets of the fuel.

The magnetic technique takes advantage of a phenomenon that occurs when a deuterium-tritium mixture, or any other gas, is heated to an extremely high temperature: the atoms of gas are stripped of their electrons. The gas 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 to the magic combination of confinement time, temperature and plasma density necessary to sustain fusion. At the Princeton University Plasma Physics Laboratory, scientists regularly heat the plasma in the Princeton Large Torus until it glows like an ectoplasmic bagel and have just achieved a density of 1014 particles per cubic centimeter, a confinement time of .10 second and a temperature of 35 million degrees Celsius.

A record plasma temperature--130 million degrees Celsius--has been attained at the University of California's Lawrence Livermore Laboratory with another variety of magnetic machine: the 2XII-B, which consists of an open-ended tube surrounded by magnets. Extra-powerful magnetic fields at the ends of the tube act as "mirrors," reflecting particles toward the center of the device and reducing leakage. But none of these or other exotic magnetic devices have yet simultaneously produced all three conditions necessary for controlled fusion.

Most scientists concede that this honor could well be won by the giant Tokamak Fusion Test Reactor (TFTR) now under construction at Princeton. The TFTR is scheduled to begin operation in 1981 and is expected to prove the scientific feasibility of fusion.

Other groups of scientists are placing their bets on a different technique: "inertial confinement." This process involves the high-power laser or electron-beam bombardment of tiny pellets crammed with deuterium and tritium. The sudden application of the energetic beams causes instant vaporization, or boiling away, of the outer surface of the sphere. As the pellet coating flies outward, it pushes back against the deuterium and tritium, compressing and heating the mixture. If the impinging beams are energetic enough, the effect will be so great that the nuclei will fuse, releasing energy like a miniature H-bomb. Among others, researchers at Los Alamos (N. Mex.) Scientific Laboratory and the Lawrence Livermore lab have achieved fusion in laser experiments with the pellets. More impressive reactions may occur in late 1977, when scientists at Lawrence Livermore complete work on the $25 million Shiva, the world's largest and most powerful laser. On the other hand, experts at Sandia Laboratories in Albuquerque are pinning their hopes for achieving fusion on the descendants of an already operating machine called Proto, which fires a beam of electrons at the pellet, zapping it with a jolt equal to 8 trillion watts.

If progress continues at the present rate, the Energy Research and Development Administration--which supplies most of the half-billion dollars now being spent annually for U.S. fusion research--predicts that by the late '70s or early '80s researchers in the U.S., U.S.S.R. and Japan could achieve "break even," or the point at which a machine produces as much power as it uses. Then researchers can concentrate on attaining ignition conditions: the time-temperature-density combinations at which the fusion reaction sustains itself. "By 1985," dreams Ronald Parker of M.I.T.'s Alcator fusion program, "we will have the first ignition device. Then we will turn off all the power except the magnets, and the gas in there will be burning just like our own little sun." After that, researchers would have to achieve the point at which a fusion reactor produces more power than it uses and then build a demonstration plant that will actually convert the enormous heat produced by fusion into electrical energy. ERDA believes that the first such facility could be ready by the mid-1990s and that fusion plants could begin supplying energy to the U.S. early in the next century.

Worthy Goal. Many obstacles remain before that day arrives. Some experts feel that even after break-even, the engineering of practical power plants will be difficult and their construction expensive. Admits Lawrence Livermore Physicist John Emmett: "No one is saying it will be cheap." Still, given the seriousness of the energy crisis, that is no reason to sidetrack fusion research in favor of programs promising quicker payoffs. "Shortrange solutions last a short time," warns Princeton Physicist Melvin Gottlieb. "Longterm solutions take decades to achieve."

The goal of fusion seems worth the work, for, as the world depletes the last of its fossil fuel, the promise of an inexhaustible supply of energy seems cheap at any price. There is enough deuterium in the oceans to supply energy --even if present demand increases a hundredfold--for 10 billion years.

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