Sun in a Bottle (15 page)

What glory beats in this idea:
Artificial suns on the earth,
Under controlled conditions.

 

 

S
hortly after the ZETA defeat came a measure of victory. Unfortunately, nobody cared.

In 1958, not long after the British scientists at Harwell retracted their claim of generating thermonuclear fusion, American physicists finally put a tiny fusion reaction in a magnetic bottle. It was not a very large reaction, and starting the fusion consumed many times more energy than the reaction produced, but they had managed to initiate fusion in the laboratory. The neutrons they detected were from thermonuclear fusion.

The machine that did it was a pinch machine, not dissimilar to Columbus or the Perhapsatron, but its pinch was arranged slightly differently. Previous devices simply zapped an electric current down the length of the plasma. The new device, Scylla, ran a current
around
the circumference of the tube of plasma instead. It was just a variant on the existing pinch machines, but the change made a big difference. Scylla was able to heat deuterium to more than ten million degrees. Scientists began to detect all the expected products of deuterium-deuterium fusion: protons, tritium nuclei, and neutrons. Tens of thousands of neutrons. With a few months of tinkering, physicists were getting roughly twenty million neutrons every time they ran the machine. It was a stunning success after so much failure.

It was just in time, too. The Second International Conference on the Peaceful Uses of Atomic Energy convened in September 1958. Though the ZETA fiasco was still on everybody’s minds, the American display of fusion machines impressed visitors. Scylla made an appearance, along with the other magnetic bottles built by Project Sherwood. The Perhapsatron was there, as was Columbus. The early Stellarators also drew a crowd. Scylla should have been the star of the show, but the Scylla scientists weren’t ready to make a formal announcement of their accomplishment. They were uncertain about whether they had truly achieved thermonuclear fusion and were well aware of the damage that a premature announcement could cause.

There were sly hints, of course. Los Alamos’s Tuck gently implied that Scylla had succeeded where ZETA had failed, but he was much more cautious than the ZETA team had been. There was no press conference, just a scientific paper that stated, blandly, that Scylla “looks probable as a thermonuclear source.” There were to be no adulatory headlines. Even when Tuck finally made a formal announcement—a year and a half later, in March 1960—it was to Congress, not to the press. “We are now prepared to stake our reputations that we have a thermonuclear reaction,” he said. Scylla had done, for real, what ZETA had falsely claimed to do, but this time the world scarcely noticed.

The quest for unlimited fusion energy was in a dramatically different state than it had been a mere two years earlier. The public’s attitude had changed: the ZETA affair and the growing concern about nuclear fallout had soured people’s perception of fusion scientists. The scientists themselves were even growing pessimistic. Gone were the heady days of the 1950s when a working fusion reactor seemed to be just a few hundred thousand dollars away. Plagued by problems and instabilities, Project Sherwood seemed to be stalling. Congress, impatient with fusion scientists’ broken promises, began to pull the plug on magnetic fusion research. Physicists raced to make some kind of discovery that would keep their quest for fusion energy alive. In 1958, the road ahead seemed dark.

In fact, there was a new reason for hope. The year brought a new and powerful idea into America’s quest to tame fusion reactions—a novel Russian design that combined the advantages of the pinch and the Stellarator. It also saw the invention of a revolutionary device, the laser, that could bottle a tiny star in an entirely new way. The magnetic bottle was no longer the only game in town. A new set of hopefuls would soon sally forth to tame the power of the sun, only to be battered by the quest.

 

 

If there was one thing that scientists at the 1958 UN conference could agree about, it was that plasmas were proving very tough to control. In part, this was because plasmas were like nothing else scientists had encountered in nature. Plasmas behaved something like fluids, but unlike standard fluids, they interacted in extremely complex ways with magnetic and electric fields. Because of that electromagnetic component, understanding plasmas was becoming an entirely new discipline vastly more complicated than the hydrodynamics field that dealt with the behavior of ordinary fluids. Plasma physicists were charting new territory in a brand-new subject: magnetohydrodynamics. Even the simplest-sounding problems with a plasma turned out not to be simple at all.

What happens, for example, when you expose a plasma to an electric current, as in a pinch machine? The laws of electromagnetism say that electrical currents spawn magnetic fields, and magnetic fields spawn electrical currents. This means that an electrical current traveling down the plasma will generate magnetic fields that generate electrical currents that generate magnetic fields, and so forth—and all these effects change the motion of the particles in the plasma, forcing them toward the center of the cloud. This is why a current causes a pinch, confining the plasma and squeezing it into a tight thread. But this pinch has secondary effects, such as causing the thread to partition itself into little segments like a set of sausage links. The people who designed the pinch machines were immediately able to spot the pinch effect, but it took deeper thought to find the secondary effect of the sausage instability. The deeper the physicists looked into plasma dynamics, the more strange effects they saw—secondary and tertiary and beyond—most of which seemed to make the plasma unstable.

This feedback between electric fields and magnetic fields is just one of many effects that make plasmas hard to predict. Another has to do with the density of the plasma. Electric currents behave differently in plasmas of different densities and pressures. A current passing through a cloud of plasma alters the shape and density of the cloud—a pinch compresses the shape and increases the density—but this change alters the nature of the current passing through the cloud. This changes the shape and density of the cloud, which alters the current, which alters the shape and density of the cloud, and so on. Yet another issue had to do with the very makeup of the plasma. Scientists had been trying to ignore the fact that a plasma is not a nice, homogeneous substance made of a single kind of particle. A plasma is made of very heavy positively charged particles (the nuclei) and very light negatively charged particles (the electrons stripped from the atoms). These two kinds of particles have different properties and behave differently even when they are at the same temperatures, at the same pressures, and subjected to the same electromagnetic fields. Physicists discovered that when they tried to heat a plasma, unless they were very careful they would pour most of the energy into the light (and easy to accelerate) electrons, leaving the heavy nuclei cold, unheated, and slow. This was really bad news. The whole point of heating the hydrogen plasmas was to heat up the nuclei so that they were moving fast enough to fuse; hot electrons and cold nuclei were all but worthless. Unless scientists could compel the hot electrons to share their energy with the nuclei, there would be no hope of fusion. For all these reasons—and more—plasmas were very hard to work with. Even before a plasma gets hot and dense enough to ignite, it is a fiendishly complex brew.

The brew did not behave the way scientists expected it to. It seemed to have a mind of its own, thwarting all attempts to keep it under control. Pinch it or squeeze it or even try to keep it confined in a magnetic trap and it writhed around and ruffled itself in instability after instability. Physicists built bigger and more expensive machines to wrestle the instabilities into submission, but they were failing. As the machines started costing millions and tens of millions of dollars, the scientists were no closer to building a fusion reactor than before; they were just uncovering more and more subtle ways that the plasma fought their will.

Lyman Spitzer’s Stellarator, for one, was mysteriously losing the particles in its plasmas. High-temperature particles move very quickly and are inherently hard to constrain. It was no surprise then that hot plasma particles in a crude magnetic bottle would rapidly spiral out of control and slam into the walls of the vessel, and the higher the temperature, the faster the particles were lost. On the other hand, increasing the magnetic field strength—strengthening the bars of the magnetic cage containing the plasma—should have rapidly brought this problem under control. That was the theory, anyhow. The researchers thought that if they doubled the magnetic field, they should cut the loss rate by a factor of four. If this theory was right, it would be fairly simple to get particle losses under control merely by cranking up the strength of the magnets surrounding the plasma. Relatively weak magnetic fields would suffice to confine even very hot plasmas.

Nature wasn’t quite so kind to the Stellarator. As the scientists turned up the magnetic fields, they were surprised to discover that particles still zoomed out of control very quickly. The particle loss rates weren’t dropping nearly as fast as the physicists’ theories had led them to expect. Even with very powerful magnetic fields, the particles still spiraled out of control in a fraction of a second. Simply turning up the strength of the fields was not enough to bring the losses down to a reasonable level. The plasma was still out of control. The American physicists were beginning to despair.

Even the optimistic Spitzer gave up his dreams of a quick and cheap path to fusion energy with a Stellarator. In the early 1950s, he had thought that his small model-A and model-B Stellarators would lead quickly to a bigger, model-C machine that would serve “partly as a research facility, partly as a prototype or pilot plant for a full-scale power producing reactor.” Spitzer was fairly certain that he would be within sight of a working fusion power plant by the end of the decade. Then, setback after setback sapped his optimism. By the late 1950s, he viewed the $24 million model-C Stellarator then under construction “entirely as a research facility, without any regard for problems of a prototype.”
⁴¹
Spitzer no longer saw fusion energy as within his grasp; a pilot plant was many generations of machines away.

It was a difficult time for fusion physics. Even the successes of Sherwood, such as Scylla’s first sighting of thermonuclear neutrons, were not showing a path to a working reactor. Making matters worse, the Atomic Energy Commission’s budget, which had skyrocketed through the 1950s, stopped growing, and the fusion research budget itself began to pinch.

These difficulties bred a measure of hope for magnetic fusion. Perhaps because the goal of a fusion reactor was so far out of reach, all the nations working on fusion energy decided to share their knowledge. The stakes had been lowered; there was no obvious path leading to limitless energy, so there was no harm in international collaboration. At the 1958 UN conference, the shroud of secrecy finally lifted from the fusion reactor programs around the world. Not only did American and British physicists have permission to lecture about the work they had done over the past decade, so, too, did their Russian counterparts. And behind the Iron Curtain, Soviet physicists had been doing some extraordinarily good work. The West soon learned of an idea that came from Russia’s version of Edward Teller: Andrei Sakharov.

Sakharov was a little more than a decade younger than Teller, so he was still a student when World War II erupted. He built a wartime reputation by working on conventional, not nuclear, munitions. He came up with a clever method to use electric and magnetic fields to detect defective armor-piercing shells, a vast improvement over the backbreaking work of snapping random shells in half to see whether they were properly manufactured. As the war was ending, Sakharov returned to school to get a graduate degree in physics, thinking he had escaped his weapon-engineering days. But on August 7, 1945, he was drawn back to military work.

On his way to the local bakery, Sakharov happened to glance at a newspaper. It told of the destruction of Hiroshima. “I was so stunned,” he wrote, “that my legs practically gave way.... Something new and awe-some had entered our lives, a product of the greatest of the sciences, of the discipline I revered.” The cloud of the atom bomb began to mushroom over his studies. As Sakharov tried to concentrate on theoretical physics, those mysterious secret cities began to spring up across the nation. His mentor, Igor Tamm, was secretly getting involved in Russia’s nuclear program. By 1948, Sakharov had been drawn into a project to design fusion weapons (the atom bomb problem having already been worked out, in part, thanks to the spying of Klaus Fuchs).

Sakharov immediately came up with his “first idea,” a design for a thermonuclear weapon. This design, the sloika bomb, was almost identical to the layered Alarm Clock design that Teller discarded as impractical in 1946. Though the sloika had the same problems as the Alarm Clock—megaton-size weapons would be too large to be practical—it offered a quick path to building a fusion device. Sakharov’s first idea impressed the Kremlin, which then whisked him away to one of the secret cities. To his dying day, Sakharov only referred to the laboratory as “the Installation,” and for a time, its mere existence was one of the most closely guarded secrets of the Soviet Union. The Installation was an entire town, code-named Arzamas-16, built for the purpose of designing nuclear weapons.

Sakharov’s intellectual trajectory was an eerie mirror image of Teller’s, always delayed by a few years.
⁴²
Teller came up with the imprac- tical Alarm Clock configuration for the hydrogen bomb in 1946; Sakharov hit on his sloika in 1949. In 1946, Teller proposed boosting the yield of a fission bomb by injecting a tiny dollop of fusion fuel (the idea tested in Greenhouse Item). Boosting atom bombs was Sakharov’s “second idea,” which came soon after his first. In 1949, Ulam and Teller solved the problem of igniting a fusion reaction by separating the primary fission device from the secondary fusion one; Sakharov and his colleagues came to the same solution—Sakharov’s “third idea”—in 1953.