Science: Controlled Fusion

A portentous rumor is spreading fast through U.S. atomic industry: that a “controlled fusion” (hydrogen) reactor has been or may soon be achieved. Nothing has come into the open, and Atomic Energy Commission officials refuse, sometimes nervously, to answer questions touching remotely on the subject. But the rumors have enough substance to worry electric power companies. In the absence of assurances to the contrary, some of them are afraid that the fission (uranium) power plants they intend to build in the near future may be hopelessly outmoded before they are finished.

Both the Russians (on July 1 Soviet Scientist M. G. Meshchiryakov reported controlled fusion experiments) and the British, as well as the U.S.. are reported to be working hard on this radical device, but the only fusion reaction demonstrated so far is an uncontrolled one: the hydrogen bomb. In the bomb, light elements (isotopes of hydrogen and probably lithium) are caused to join into helium by the intense heat of an exploding fission (uranium) bomb. Something more tractable is needed to start a fusion reaction in a peaceful power plant.

Hot Spot. The problem is a favorite one with nuclear inventors, and there have been many suggestions. Most of them use electrical methods for generating intense heat in very small amounts of material. A beam of electrons from a linear accelerator, for instance, carries a good deal of energy. If it is focused on a small spot, perhaps one-thousandth of a millimeter in diameter, it will raise the temperature of that spot to many million degrees.

No known material can stand such heat, but if the material struck by the electrons is lithium-six deuteride,* it will (so say the rumors) turn into helium, giving off a vast amount of energy.

What happens next is known only in the innermost nuclear circles, if it is known there. Some outside guessers think that the reaction, once started, will be self-sustaining. The nuclear fire will sweep through the lithium deuteride like a flame through dry excelsior. Others believe that the reaction will have to be stimulated, continuously or intermittently, by energy from outside.

Intermittent Control. Ways of controlling the reaction are under debate too. One way would be to make it intermittent, with a very small amount of nuclear fuel present at a time. This would make the fusion reactor analogous to a reciprocating gasoline engine, where minute amounts of fuel are ignited and burned in series. But it might also be possible to make the reaction proceed at the desired rate by changing in some way the physical conditions in the reaction chamber.

It does not take a physicist to see that if a fusion reactor works with reasonable efficiency it would have great advantages:

¶ Its fuel would be extremely cheap in terms of energy yield, much cheaper than uranium.

¶ There would be no radioactive fission products. This is important because the safe disposal of this dangerous material imposes a heavy cost burden on a uranium power reactor.

¶ Its radiation might be comparatively easy to handle, requiring lighter shielding. This would be a great advantage in propulsion reactors, especially of aircraft.

¶ The fusion reactor might not contain a large amount of radioactive fuel, as uranium reactors do. If so, it would be less hazardous. The possibility, however remote, that a uranium reactor may explode and spray the neighborhood with radioactivity is a serious problem.

¶ If a fusion reactor should turn out to be successful, the booming uranium mining industry would be threatened with infant mortality.

* Chemical compound of lithium’s light isotope, Li and hydrogen’s middle isotope, H².