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By Root 1415 0

nothing to nearly $30 million a year by the time of the 1958 UN conference. As the Stellarator began to choke, losing its plasma rapidly, a skeptical Congress began to wonder whether fusion reactors were possible at all, much less economically feasible. It didn’t help that the scientists, in their optimism, had consistently oversold their machines. They had promised Congress they would be building prototype reactors by the early 1960s, and the machines were nowhere near that stage. And in October 1957, the Russian surprise launch of Sputnik gave the Earth an artificial moon—and it gave Congress another Cold War scientific competition requiring truckloads of taxpayer money. The space race had officially begun. Fusion energy was no longer in the spotlight, and its budget stagnated, then dwindled.

The tokamak had to come to the rescue, but it would be several years before American and British scientists would accept that the Russian achievements were real. It was not for lack of data; Artsimovich continued presenting better and better results—dense plasmas heated to tens of millions of degrees and confined for handfuls of milliseconds. The tokamak results were still far from those needed for a realistic source of fusion energy, but they were certainly an order of magnitude better than anyone else’s. The work was getting harder to dismiss, but detractors still argued that the Russian temperature measurements were inaccurate. To settle the matter, in 1969 a British team visited Artsimovich’s lab in Moscow. They came armed with a sensitive instrument that could measure the temperature of a ten-million-degree plasma.43 At the heart of the instrument was a device that would change the face of fusion research, and not just because it confirmed the Russian claims. It would provide a new way of bottling a plasma without the use of magnets. The device was the laser.

Depending on whom you ask, the laser was invented at Columbia University in the late 1950s or at Hughes Research Laboratories in 1960. (There were competing claims and a patent battle.) But there’s no doubt that in 1960 a short paper in Nature gave the physics community a powerful new tool.

A laser is a device that produces an unusual beam of light. Even to the uninitiated, it is obvious that laser light is different from, say, the light that comes from a flashlight. If you shine a flashlight at a distant wall, you will see that it makes a large, circular spot. If you shine a laser pointer at the same wall, it makes only a tiny dot, barely larger than the hole from which the laser beam emerged. Laser light stays together in a tight beam rather than spreading out into a diffuse cone. A laser beam also consists of light that is a single, intense color,44 unlike a flashlight beam, which is made of a whole bunch of colors mixed together and appears white.

There are many methods of generating light. If you heat something high enough, it begins to glow. When a substance is energetic enough, it emits visible light. (This is how an incandescent lightbulb works; the filament in the bulb is simply heated to a very high temperature.) It is a law of nature: the hotter an object is, the more light waves it emits. Or, if you prefer, you can think of the emissions as light particles rather than light waves. The laws of quantum theory say that light has both a particle-like and a wave-like nature, so physicists use whichever description is most suitable for the behavior they are attempting to describe.

A particle of light—a photon—can interact with matter in a number of different ways. It can strike an atom and give it a kick. It can make the atom rotate or move in other manners. If the photon is just the right color, the atom can absorb it. Absorbing a photon “excites” the atom, packing it full of the energy that once resided in the light particle. This excited atom will soon disgorge the photon, emitting a light particle of precisely the same color and relaxing from its excited state.

In 1917, Albert Einstein made a curious prediction about excited atoms. Such an atom is quivering