Sun in a Bottle_The Strange History of Fusion and the Science of Wishful Thinking

by Charles Seife

  The enthusiasm surrounding the technology, though, hid a lot of difficulties—and some infighting. Spitzer and the Princeton Stellarator team thought their idea was the path to fusion energy, and tried to tear down the Perhapsatron idea championed by their rival, Los Alamos’s Tuck. In fact, Spitzer spent some of his AEC grant trying to prove that a Perhapsatron would not work. It was money well spent. Two of his team members, Princeton professors Martin Schwarzschild and Martin Kruskal, found a very disturbing flaw that threatened to disrupt the Perhapsatron research program altogether. A pinched plasma was unstable.

  Perhaps the easiest way to understand stability and instability is to imagine a ball sitting at the bottom of a hill. This is a stable system. Give the ball a slight nudge and it will roll right back to where it started. The system resists change; it won’t be ruined by small perturbations. A ball perched on the top of a steep hill, on the other hand, is in a precarious position. Give it even the slightest nudge and it will roll down the slope, abandoning its previous place. This system doesn’t resist change—indeed, even a tiny disturbance will change it dramatically. This is an unstable system.

  Kruskal and Schwarzschild had discovered that a pinched plasma was like a ball perched on a hill. The slightest disturbance would destroy it. Send a current through a cylinder of plasma and it indeed squashes itself into a dense little filament of hot matter. But the filament is unstable. If it is not perfectly straight, if it has even the tiniest kink, the magnetic fields generated by the pinching current immediately exaggerate and expand the kink. This makes the kink grow, getting more and more pronounced. Any little imperfection in the plasma filament rapidly becomes a huge imperfection. In a tiny fraction of a second, the plasma kinks, bends, and writhes out of control.

  As soon as the Perhapsatron started up in 1953, the Princeton team’s calculations were proved correct. The Los Alamos experimenters found that as soon as they got a pinch, forming a nice, tight filament in the center of the Perhapsatron’s chamber, it went poof! The pinch would disappear, setting the whole chamber aglow. High-speed cameras revealed the filament buckling and writhing, quickly striking the walls of the chamber. The kink instability had claimed its first victim. The Perhapsatron, as built, was incapable of fusing anything at all. The Los Alamos scientists needed to figure out how to stabilize the filament if they were to progress. They tried using an external magnetic field to “stiffen” the plasma filament somewhat, but the essential instability remained. Pinches were in trouble.

  KINK INSTABILITY: If a pinching plasma has even a tiny kink in it, that kink will grow; the plasma will writhe out of control and hit the walls of its container.

  Soon, the other designs were as well. In 1954, Edward Teller figured out that a plasma held in place by magnetic fields was unstable under certain conditions. The magnetic fields behave somewhat like a collection of rubber bands: as the plasma pressure increases, they try to relieve the increasing tension by writhing. “They try to snap inward and let the plasma leak out between them,” Teller wrote. This system was also unstable. Even a tiny irregularity in the magnetic field would rapidly get worse, and scientists would lose control of the plasma. The so-called Teller instability affected the Stellarator as well as Livermore’s magnetic mirror approach. Instabilities were everywhere.

  By the mid-1950s, all three groups had enormous difficulties to overcome. Their plasmas were unstable and their bottles were leaky. They spent ever-increasing amounts of money building bigger and more elaborate machines in attempts to get unstable plasmas under control. The few hundred thousand dollars spent on magnetic fusion in the early 1950s turned into nearly $5 million by 1955 and more than $10 million by 1957. Plans for reactors also got more ambitious: by 1954, Spitzer was suggesting that $200 million would buy a machine that would produce thousands of megawatts of power—bigger than the biggest power plants around.

  Despite Spitzer’s bold plans, Teller’s Livermore got the largest share of funding, about half of the Project Sherwood money. Princeton came in second, and Los Alamos, with its pinch program, was a distant third. Yet it was Los Alamos that first claimed victory.

  By the beginning of 1955—just before Bhabha’s speech at the UN conference brought worldwide attention to the promise of fusion energy—the Los Alamos researchers saw indications that their plasma was hot enough to fuse deuterium. Every time they initiated a strong, fast pinch in their latest machine, the scientists saw a burst of tens of thousands of neutrons. This was very encouraging, because neutrons are the best indicator of a fusion reaction.

  Everyone in the fusion community was hoping to achieve two main kinds of thermonuclear fusion in a reactor. The easier kind used a mixed fuel: deuterium and tritium. When a deuterium (a proton and a neutron) and a tritium (a proton and two neutrons) strike each other hard enough, they fuse, creating helium-4 (two protons and two neutrons). The remaining neutron flies off with a great deal of energy. So in a successful deuterium-tritium reaction, the products will be helium-4 and neutrons. Deuterium-deuterium reactions are a little more complicated; there are two ways this kind of fusion reaction tends to happen. As the two deuterium nuclei collide and stick, either a proton flies off (leaving behind a tritium nucleus) or a neutron flies off (leaving behind a helium-3 nucleus). These two branches of the reaction are roughly equally probable. Thus, if a reactor succeeds in fusing deuterium fuel, then the products will be helium-3, tritium, protons, and neutrons. Neutrons are produced by both deuterium-tritium and deuterium-deuterium fusion reactions. A burst of fusion—no matter whether the fuel is pure deuterium or deuterium mixed with tritium—will be accompanied by a corresponding burst of energetic neutrons.37

  FUSION REACTIONS: (a) Two deuteriums collide and produce either a tritium and a proton or a helium-3 and a neutron. (b) A deuterium strikes a tritium and produces a helium-4 and a neutron.

  Despite the problem with the kink instabilities, Los Alamos scientists were optimistic. If they could make the pinch strong enough and fast enough, they thought, they could get fusion going before the kink instability destroyed the pinch. In fact, Tuck’s calculations showed that such a machine could achieve breakeven—the fusion reaction in the machine would produce energy equal to what was needed to get the reaction going in the first place. (A fusion reactor that absorbs more energy than it produces is of no use to anyone.) And, Tuck argued, a larger machine could produce explosions equivalent to several tons of TNT per pinch. These explosions could be turned into usable energy, just as an internal combustion engine makes little fuel-air explosions turn a crank. Tuck built successively bigger pinch machines that could pinch the plasma harder and faster, and eagerly awaited neutrons produced by thermonuclear fusion.

  When, early in 1955, the Los Alamos researchers turned on their newest, biggest pinch machine, Columbus I, they saw a burst of neutrons every time they pinched the plasma hard enough. Pinch. Neutrons. Pinch. Neutrons. No pinch, no neutrons. It seemed like a great success. From the number of neutrons they were seeing, the pinch scientists concluded they had attained fusion; the plasma inside the Columbus machine must have been heated to millions of degrees Celsius. But not everybody was convinced. Researchers at Livermore were skeptical that the pinch machine could reach the temperatures advertised. Thus, the plasma couldn’t possibly be hot enough to ignite a fusion reaction. So where were the neutrons coming from?

  The Los Alamos physicists started making careful measurements on their pinch machine to see if they could pin down the origin of those neutrons. To their chagrin, they soon discovered that the neutrons coming out the front of the Columbus machine were more energetic than the ones coming out the rear. In a true thermonuclear reaction, during which nuclei in a hot plasma are fusing with one another, the neutrons from the reaction should be streaming out in all directions with equal energy. This was not the case with Columbus, so, clearly, the Columbus neutrons weren’t coming from thermonuclear fusion. They were coming from somewhere else.

  The asymmetry provided a crucial clue
. The scientists pinched the plasma by running a current through it. Neutrons that were flying out of the machine in the direction of the current had more energy than those that flew out against it. This revealed that the neutrons were the work of another instability. Just as a pinched filament is unstable when kinked slightly—because the kink grows and grows—it is unstable when a small section gets pinched a little bit more than the rest of the plasma. In this case, the small pinch grows progressively more pronounced; the plasma gets wasp-waisted and pinches itself off. The plasma begins to look like a pair of sausages. This is a sausage instability, and it creates some strong electrical fields near the pinch point. These fields accelerate a small handful of nuclei in the direction of the pinch current. These nuclei then strike the relatively chilly cloud of plasma and fuse, releasing neutrons.

  From fusion scientists’ point of view, this kind of fusion was worthless. Scientists were hoping to get a hot cloud of nuclei fusing with itself, a thermonuclear fusion reaction. Instead, Columbus had made a small handful of very hot nuclei interact with cooler ones. This was roughly equivalent to shooting nuclei at a stationary target, and doing that, scientists had concluded, would always consume more energy than it produced. The neutrons produced by the instability, dubbed instability neutrons or false neutrons, weren’t a sign of energy production—just the opposite. Columbus’s neutrons were the sign of energy consumption, not energy production. The false neutrons had given the Los Alamos scientists false hope. Even so, the pinch technique still seemed within striking distance of igniting fusion.

  SAUSAGE INSTABILITY: If a pinching plasma is slightly narrower in one place, that narrowing will get more and more severe and eventually squeeze the plasma to make it look like a pair of sausages.

  By this time, the Americans knew they had competition from both the Russians and the British. Project Sherwood poured increasing amounts of money into ever-larger machines of all types. The most expensive one in the Sherwood portfolio was the model-C Stellarator proposed by Spitzer, which would cost roughly $16 million to design and build. So it was a humiliation when it appeared that the British had won the fusion race with a much smaller and less-expensive machine: ZETA.

  ZETA, which had cost less than $1 million to build, was a powerful pinch machine. Its name reflected the optimism of its designers; ZETA was an acronym for Zero-Energy Thermonuclear Assembly, thermonuclear because it would achieve fusion and zero-energy because it would produce as much energy as it consumed. It was a very bold claim.

  ZETA began operation in mid-August 1957 at the Harwell laboratory near Oxford. It wasn’t long before the machine made a big splash. Late in the evening of August 30, the ZETA device started producing neutrons. The scientists did hasty checks to make sure there wasn’t an equipment failure of any sort; the neutrons were real. Pinch. Neutrons. Pinch. Neutrons. Like their American counterparts before them, the British physicists thought the neutrons were the signature of fusion; after all, neutrons were the smoking gun that everybody had been seeking for so long. There were a few skeptics on the ZETA team—some doubted that ZETA had actually achieved fusion—but the joyful chorus of self-congratulation drowned out the voices of doubt. The mood was jubilant. Most of the ZETA team thought they had finally done it; they had built the first, rudimentary, artificial sun. The physicists present popped open a bunch of beers to celebrate.38

  After weighing the evidence and crunching the numbers, the physicists at Harwell concluded that the plasma in the ZETA machine was reaching a temperature of five million degrees with every pinch, creating thermonuclear reactions and producing neutrons. If so, this was big news. It would be the first time that scientists had achieved fusion in a controlled environment. The British team naturally wanted to release their initial results right away, revealing the brilliant future of limitless energy to the public. But the Americans balked.

  Earlier in the year, the British and Americans had decided to share data on fusion reactors with each other, and they were to decide jointly when and how to declassify the data and release it to the public. This last point became a source of contention. The Americans were reluctant to make an announcement about ZETA, in part because Project Sherwood had no signal achievements to brag about at the time. It looked as though the Brits had beaten the pants off the Yanks, so the Yanks needed some time to catch up. Thus, citing security issues, the United States tried to delay the announcement for a year. A second United Nations conference was scheduled for 1958, and what better place was there, U.S. officials argued, to release the results?

  The British were unhappy about the American insistence on secrecy, and it is hard to keep a secret if one party wants to reveal it. Naturally, the secret didn’t stay secret for very long. By early September, news of ZETA’s success was leaking out. The English press was buzzing with rumors of successful nuclear fusion in the ZETA machine. By October, British scientists—including the Nobel laureate and Harwell lab head, John Cockcroft—hinted at encouraging results from the device. However, in deference to the Americans, nobody made an official pronouncement.

  Hints about ZETA’s success got harder and harder to ignore. In November, a spokesperson for the British Atomic Energy Authority (BAEA) stated, “The indications are that fusion has been achieved” at ZETA, but gave no further details. English scientists briefed the House of Commons on their achievement. But the weeks ticked away without any description of what, exactly, had happened at Harwell.

  The mystery deepened in December. Even as the BAEA denied that the United States was deliberately “gagging” ZETA scientists, preventing them from releasing their results, a BAEA spokesman admitted that Britain was awaiting American approval to publish the details of the Harwell experiment. The British press was infuriated and accused the United States of playing politics with a crucial scientific achievement, of needlessly delaying publication of an important experimental result. The British had beaten the Americans at their own game, and Lewis Strauss and the Project Sherwood crew seemed to be holding up the declassification process to give themselves time to catch up to the Brits.39

  To the ZETA scientists, it was more than merely frustrating. Without a publication, it was as if the experiment had never happened. In science, publication is everything; without it, an experiment is worthless. It is easy for anybody to make an outrageous scientific-sounding claim. If you use the right buzzwords, you can make it extremely convincing; you can easily make the public believe that your claim is true. That’s what happened with Ronald Richter. Given a platform by Juan Perón, Richter trumpeted a remarkable achievement—based on pseudoscience—around the globe. Important people, including Perón, believed him. But very few scientists did. That is because Richter did not publish any scientific data that would have allowed specialists to verify his claim. To a scientist, an experiment is not believable without the precise details of how it was run and what the researchers involved observed. Only when scientists reveal the inner workings of an experiment to the world can their peers scrutinize the work and confirm or refute it. Only then will they be taken seriously. By blocking the publication of the ZETA results, the Americans were denying the British their chance at scientific glory.

  Finally, the Americans succumbed to the pressure and gave Britain the go-ahead to publish the ZETA findings. When the Harwell scientists announced, in mid-January, that they were publishing their results in Nature at the end of the month, the British press was ecstatic. When they learned that the ZETA papers were to be accompanied by papers about Project Sherwood’s pinch project, the press was absolutely livid. It looked as if Lewis Strauss and the Americans, with their expensive machines, were trying to steal some of the Harwell laboratory’s glory. “Admiral Strauss’ tactics have soured what should be an exciting announcement of scientific progress so that it has become a sordid episode of prestige politics,” blared the British Sunday Observer. Despite the hurt feelings, everyone was relieved that the long wait was about to end.

  When the Nature papers finally came
out on January 24, the British and American scientists held a joint press conference. John Cockcroft announced that it was “90% certain” that ZETA’s neutrons had come from fusion, and outlined a twenty-year research plan that would lead to fusion reactors. The Americans presented their results, too, but they weren’t nearly as striking as ZETA’s. The press in the United States spun the story as a great British-American achievement. “Gains in Harnessing Power of H-Bomb Reported Jointly by U.S. and Britain,” the New York Times declared; “Nations Called Equal—Many Questions to Be Resolved.” America’s Columbus II machine was given pride of place above Britain’s ZETA, and the newspaper emphasized that the two nations were “neck and neck.” However, the rest of the world’s press ignored the American research and celebrated Britain’s triumphant conquest of fusion energy. In England, tabloid papers blasted the news across their pages, promising “UNLIMITED POWER from SEA WATER”: no more electricity bills, no more smog, no need for coal, power that would last for a billion years. Newspapers around the globe followed suit; they were quick to trumpet the prospect of limitless energy, energy that would be at humanity’s fingertips within two decades. No longer would any nation be held hostage because of a lack of oil. Even the Soviets congratulated the British—pointedly ignoring the Americans—on their “achievement in harnessing thermonuclear energy” and expressed their “admiration.”40 ZETA seemed to have begun a new era of humanity, the era of unlimited fusion energy, and it was the envy of the world.