Magnetic Bottle

Project Sherwood, the secret U.S. program to achieve controlled thermonuclear (atomic fusion) power, came ever so slightly into the open last week. After attending a secret conference of 350 Sherwood men at Gatlinburg, Tenn., Dr. Edward Teller, leading authority on thermonuclear processes, delivered a complicated paper before an unclassified meeting of the American Nuclear Society at Chicago.

Teller's speech did not give the present status of U.S. thermonuclear research, but it did give a great deal of background, new to most outsiders, about the path (or one of the paths) that Project Sherwood is following.

Small Star. In the stars, said Teller, thermonuclear reactions are possible because the great mass of the star provides a gravitational field that holds the reacting gases together, even though their temperature may be very high. Human scientists have better nuclear fuel than the stars have, but they cannot hold their gases together gravitationally. No material container can do the trick, either; its walls would be melted instantly if they came in contact with reacting gases at the necessary high temperature.

One way to create a "small star" that reacts at enormous temperature without touching anything material is to confine the gases in a "magnetic bottle." Teller explained that the gases would be completely ionized by the heat. All the particles in them would have electric charges, and would be strongly influenced by a magnetic field. If the field could be made strong enough, the particles would spiral tightly in it, keeping away from vulnerable walls of the material container.

Tricky Balance. Leakproof magnetic bottles, Physicist Teller pointed out, are not easy to construct. The magnetism must be just strong enough to confine the ionized gases at the right density and temperature, and keep them confined long enough for a reaction to take place. The reaction would release energy and raise the temperature, so the magnetic field must grow stronger when necessary to keep things in balance. Power must be drawn out of the system without disturbing its tricky balance.

Teller did not tell in detail how this could be done, but he gave a long chain of complex equations showing how energy is released in reacting gases (deuterium or tritium), and how energy escapes from the system. He gave a few general hints about how the lines of magnetic force affect and confine the moving ions. He did not sound lightly confident; repeatedly, he pointed to serious difficulties.

But Teller believes that the job can be done, given enough time and effort. "I am confident," he said, "that controlled thermonuclear reactors will eventually be constructed. I do not believe that the power derived from such reactors will compete at an early date with conventional energy sources or with fission [uranium] reactors."

When thermonuclear reactors are finally achieved, said Teller, they will have several advantages. Their fuel, deuterium, is inexhaustible and it needs no processing after it has been separated from common hydrogen. They will become highly radioactive because of neutrons released within them, but unlike atomic fission reactors they will not contain large amounts of dangerous radioactive material that might be scattered by an accident. On the other hand, they will probably be harder to operate and maintain.

The most exciting possibility Teller mentioned last. It is at least theoretically possible, he said, that a thermonuclear reactor may yield electric power direct, without costly and inefficient turbines, generators, etc. This is almost out of the question with uranium reactors, but the "magnetic bottle" of the thermonuclear reactor is electrical to start with. "If we shall have learned," said Teller, "how to confine a plasma of considerable pressure by a magnetic field, then it should not be too difficult to extract energy from the plasma by varying the magnetic field."

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