Sun in a Bottle (12 page)

The visit was a fiasco. Richter showed the scientists his fusion reactions. In the reactor chamber, vivid red lithium and hydrogen flames spewed forth; the dials of the Geiger counters fluttered. The scientists weren’t impressed. Neither were the gamma-ray detectors that the physicists brought with them. Unlike Richter’s Geiger counters, the gamma-ray detectors showed no evidence of radiation whatsoever—radiation that had to be there if, indeed, fusion was occurring. Stranger still, when they exposed Richter’s equipment to a real source of radiation—a piece of radium—the counters didn’t chirp at all. The equipment had been rigged. The Geiger counters weren’t responding to radiation but to the electrical discharge that ignited the ersatz fusion reaction. At best, Richter was deluded. At worst, he was a fraud. Even Perón, Richter’s biggest backer, had to admit that Richter’s nuclear fusion was a farce.

The failed Huemul project quickly became an embarrassment for Perón. Richter began to face accusations from Argentina’s legislators, and in December, despite official denials, the Argentine dream of fusion energy was over. Rumors of Richter’s incarceration began to appear in the press, but in truth it was two more years before he was finally arrested.

Perhaps it was naïveté or optimism that drove him; perhaps it was greed. Perhaps it was the desire for power. Whatever the reasons for Richter’s bold claims, he had wasted millions of dollars’ worth of Perón’s money in his pursuit.
³³
If he had succeeded, Perón’s Argentina would have solved the world’s growing energy crisis overnight. Humanity would have considered Richter its savior.

Instead, Richter found himself accused of fraud, scorned and humiliated. He was just the first casualty of the quest to put the sun in a bottle.

 

 

Lyman Spitzer, a physics professor at Princeton University, was about to leave for a ski trip to Aspen in March 1951 when the papers broke the story about Richter’s fusion reactor. Spitzer was instantly incredulous, but at the same time he was intrigued. On the ski slopes, he wondered just how to make a device that could hold a miniature sun. By the end of his sojourn, Spitzer was well on his way to designing one. Instead of using nuclear weapons to contain fusing hydrogen, Spitzer would exploit the odd properties of extremely hot matter, properties of what physicists call a
plasma
.

Heating an object changes the way it behaves. A frozen hunk of water is solid ice. Put it on a table and it will retain its shape. Heat it a bit and the ice changes, melting into a liquid. Though liquid water still has a definite volume, it no longer has a fixed form; it will change its shape to fit whatever container you put it in. Heat it some more and the fluid changes again. The water boils into a gas: steam. As a gas, the formless cloud no longer even has a definite volume. A gas expands or contracts, depending on the pressure and temperature of its surroundings. As matter gets hotter and hotter—more and more energetic—its atoms’ random dancing speeds up and it eventually changes from solid to liquid to gas. This much scientists knew for centuries. Only at the end of the 1800s did physicists begin to realize that extremely hot gases changed their properties yet again. The reason has to do with the composite nature of the atom.

GAS VERSUS PLASMA:
In a gas (left), every electron is stuck to an atom. In a plasma (right), the electrons roam free, attracted by nuclei, but not attached to any single nucleus.

As scientists realized at the beginning of the twentieth century, atoms are not quite as uncuttable as their name would imply. Protons and neutrons sit in the center of the atom, making up a small, dense, heavy, positively charged nucleus. Surrounding the nucleus are light, negatively charged electrons. Ordinarily, electrons are bound to a nucleus; the opposite charges of the protons and electrons attract each other, so the electrons cannot easily shake free. In fact, the nucleus and the electrons attract each other so strongly that the whole mess behaves very much like a single object.

Yet this isn’t always the case. Raise the temperature and the atoms start moving faster and faster. There’s a lot of energy about, and some of that energy winds up exciting the electrons. If the temperature is hot enough, the electrons get so excited, so pumped full of energy, that they can escape the bonds of their nuclei, and the atom loses an electron. As the temperature rises, the available energy increases, the electrons become more excited, and one by one they escape their bonds.
³⁴
Finally, at a high enough temperature, all the electrons are stripped from their nuclei.

The electrons are still nearby, unattached to any particular nucleus. Unbound electrons and nuclei roam in one big blob, unattached to each other. At extremely high temperatures a hunk of hot matter becomes an undifferentiated soup of unconnected negatively charged electrons and positively charged nuclei.

This is a plasma. Pour enough energy into a piece of matter—heat it enough—and atoms lose their individuality. The positively charged nuclei are still attracted to the negatively charged electrons, but they are not bound together. And this gives a plasma some unusual properties. Unlike most kinds of ordinary matter—unlike most solids, liquids, and gases—the free-floating electrons and protons of a plasma are strongly affected by electric and magnetic fields.

To Lyman Spitzer, this suggested a design of a bottle that could hold a miniature sun. Spitzer’s bottle would not be made of steel or stone or diamonds. It would not be made of any kind of material at all; after all, nothing would be able to stand up to the immense heat of a fusion reaction. Spitzer’s bottle would be made of invisible lines of force: it would be made of magnetic fields.

By the twentieth century, these fields were extremely well understood. Physicists had long been amazed by the intricate interplay of electric fields, charged particles, and magnetic fields, but in the nineteenth century, physicists figured out that these interactions are governed by only a handful of relatively simple rules. Nonetheless, even simple rules can have seemingly complicated consequences.

For example, the laws of electromagnetism dictate that moving charges are affected by magnetic fields, while stationary ones are not. It’s a quirky-sounding rule, but it’s what the equations dictate: if you put a stationary charged particle (like a proton) in a magnetic field, it won’t feel the field at all. A charged particle that is moving, on the other hand, is tugged and deflected by a magnetic field. More specifically, a moving charged particle feels a magnetic pull perpendicular to its motion. This force makes the particle change course. Instead of moving in a straight line, the particle moves in a circle, and the stronger the magnetic field, the tighter the circle. Conversely, the equations of electromagnetism dictate that a moving electric charge (like an electron moving down a wire) will generate a magnetic field. A stationary electric charge won’t. In mathematical terms, these are pretty simple rules to describe. But just these rules can give you a hint of how complicated a plasma must be.

In a plasma, you have a large number of charged particles—electrons and nuclei—moving about at relatively high speeds. These moving particles generate magnetic fields. These magnetic fields change the motion of the moving particles. When the motion of the moving particles change, so do the magnetic fields that they are generating—which changes the motion of the particles, changing the magnetic fields, and so on. Add to that the electric attraction that the electrons and nuclei feel for each other and you’ve got an incredibly complex soup.

Nevertheless, to Spitzer, the mere fact that the plasma responds to magnetic fields suggested a way to bottle it up. He realized that if you had a plasma moving through a tube and you subjected that tube to a nice, strong magnetic field in the proper orientation, the charged particles in the soup would be forced to move in little circles. They would spiral down the tube in tight little helices, confined by the magnetic field, never even getting close to the walls of the cylinder. The plasma would be confined. In theory, even an extremely hot plasma could be trapped in such a bottle. Furthermore, it was fairly easy to generate the right sort of magnetic field: just wrap a coil of wire around the tube and put a strong current through it; the moving charges in the wire create just the sort of field that is needed. It was a simple, but powerful, idea.

The only problem with Spitzer’s tube was that it bottles the plasma on the sides, but not at the front or the back of the tube. When the moving plasma reaches the end of the tube, it spills right out. So what to do? Spitzer’s next clever idea was to imagine a tube without end: a donut. Such a donut (or a
torus
, as physicists and mathematicians like to call it) is just a tube that circles back upon itself. The plasma would move around and around in a circle, never spilling out the end of the tube. With the right magnetic field, it would be a perfect bottle.

Unfortunately, the very curvature that gets rid of the end of the tube makes it very difficult to set up the right kind of magnetic field. The straight tube merely needed a wire curled around it. But when you bend that tube into a donut, the loops of wire on the inside of the donut get bunched up and those on the outside get stretched and spaced out. As current flows down the wire, the magnetic field is stronger where the loops of wire are close together—near the donut hole—and weaker at the edge where the loops are far apart. The nice, even magnetic field in the tube is destroyed; it becomes an uneven mess with a strong side and a weak side. This unevenness is a big problem: it causes the nuclei and electrons in the plasma to drift in opposite directions and into the walls of the container. The bottle quickly loses its contents. It leaks. A straight tube leaks out its ends; a curved tube leaks through its sides.

Even though a torus-shaped bottle would be leaky, Spitzer quickly came up with a design to minimize the leak. Instead of a simple donut, he reasoned, it would be better to have two half donuts. These half donuts would be connected by tubes that crossed each other: a figure eight. The half-donut sections have the same problem as the full-donut bottle: the electrons and nuclei drift in opposite directions. However, because the tubes cross each other, the plasma winds up going through one half donut clockwise and the other one counterclockwise. This means that the drift on one side should be cancelled by an equal and opposite drift when the plasma goes through the other half donut. It doesn’t
quite
work that way; the drifts don’t cancel exactly, and the plasma still leaks out a bit, but the leak isn’t quite as severe as it would be in a torus-shaped bottle.

The figure-eight bottle was a good enough design for Spitzer to begin experimenting. In July 1951—as the Huemul controversy continued raging in the press—Spitzer got a grant from the Atomic Energy Commission and set to work at Princeton, generating a serious design for a figure-eight-shaped fusion reactor: the Stellarator.

The Stellarator wasn’t the only fusion reactor in town. Shortly after the Livermore laboratory was founded, some of its scientists proposed a slightly different shape for a magnetic bottle. They would stick with a straight tube. Instead of wrestling with the problems caused by curving the plasma’s path, they would try to cap the ends of the tube by tweaking the magnetic fields slightly. Strong magnetic fields at the ends of the tube and slightly weaker magnetic fields at the center would create barriers that would behave almost like a mirror. Some—not all—of the plasma streaming to the end of the tube would be reflected back inside. This
magnetic mirror
was extremely porous, so it was clearly not a perfect bottle, but neither was the Stellarator. The Livermore scientists got down to work.

A third contender came from across the Atlantic. In the late 1940s, British scientists were also beginning to think about confining plasma, and their method relied on an entirely different phenomenon that they called the “pinch” effect.

A pinch starts with a cylinder of plasma. Since the electrons are free to move around inside the cloud, the plasma itself conducts electricity; it’s almost like a piece of copper. You can send an electric current along a plasma cylinder just as you would along a copper wire. And just as in a copper wire, the current running down the plasma creates a magnetic field. But this magnetic field affects the particles in the plasma; it forces them toward the center of the cylinder. The current compresses the cylinder, crushing it toward its central axis. The stronger the current, the greater the effect, and the faster and tighter the plasma gets squashed. As an added benefit, the squashing heats the plasma. This is the pinch effect.

British scientists immediately seized on this effect as a way to confine and heat a plasma until it begins to fuse. Several British laboratories began work on pinch projects, particularly Oxford University’s Clarendon, and neighboring Harwell, a few miles away. James Tuck, a physicist who had been involved with the Manhattan Project, worked briefly on the Clarendon fusion project before returning to Los Alamos, bringing the pinch idea with him.