Authors: Michio Kaku
Physics of the Future: How Science Will Shape Human Destiny and Our Daily Lives by the Year 2100 (42 page)
The shock was immediate. Almost every newspaper in the world put this discovery on its front page. Overnight, journalists talked of ending the energy crisis and ushering in a new age of unlimited energy. A feeding frenzy hit the world media. The state of Utah immediately passed a $5 million bill to create a National Institute for Cold Fusion. Even Japanese car manufacturers began to donate millions of dollars to promote research in this hot new field. A cultlike following began to emerge based around cold fusion.
Unlike Richter, Pons and Fleischmann were well respected in the scientific community and were glad to share their results with others. They carefully laid out their equipment and their data for the world to see.
But then things got complicated. Since the apparatus was so simple, groups around the world tried to duplicate these astonishing results. Unfortunately, most groups failed to find any net release of energy, declaring cold fusion a dead end. However, the story was kept alive because there were sporadic claims that certain groups had successfully duplicated the experiment.
Finally, the physics community weighed in. They analyzed Pons and Fleischmann’s equations, and found them deficient. First, if their claims were correct, a blistering barrage of neutrons would have radiated from the glass of water, killing Pons and Fleischmann. (In a typical fusion reaction, two hydrogen nuclei are slammed together and fuse, creating energy, a helium nuclei, and also a neutron.) So the fact that Pons and Fleischmann were still alive meant the experiment hadn’t worked. If their experiments had produced cold fusion, they would be dying of radiation burns. Second, more than likely Pons and Fleischmann had found a chemical reaction rather than a thermonuclear reaction. And last, the physicists concluded, palladium metal cannot bind hydrogen atoms closely enough to cause the hydrogen to fuse into helium. It would violate the laws of the quantum theory.
But the controversy has not died down, even today. There are still occasional claims that someone has achieved cold fusion. The problem is that no one has been able to reliably attain cold fusion on demand. After all, what is the point of making an automobile engine if it works only occasionally? Science is based on reproducible, testable, and falsifiable results that work every time.
But the advantages of fusion power are so great that many scientists have heeded its siren call.
For example, fusion creates minimal pollution. It is relatively clean, and is nature’s way of energizing the universe. One by-product of fusion is helium gas, which is actually commercially valuable. Another is the radioactive steel of the fusion chamber, which eventually has to be buried. It is mildly dangerous only for a few decades. But a fusion plant produces an insignificant amount of nuclear waste compared to a standard uranium fission plant (which produces thirty tons of high-level nuclear waste per year that lasts for thousands to tens of millions of years).
Also, fusion plants cannot suffer a catastrophic meltdown. Uranium fission plants, precisely because they contain tons of high-level nuclear waste in their core, produce volatile amounts of heat even after shutdown. It is this residual heat that can eventually melt the solid steel and enter the groundwater, creating a steam explosion and the nightmare of the China Syndrome accident.
Fusion plants are inherently safer. A “fusion meltdown” is a contradiction in terms. For example, if one were to shut down a fusion reactor’s magnetic field, the hot plasma would hit the walls of the chamber and the fusion process would stop immediately. So a fusion plant, instead of undergoing a runaway chain reaction, spontaneously turns itself off in case of an accident.
“Even if the plant were flattened, the radiation level one kilometer outside the fence would be so small that evacuation would not be necessary,” says Farrokh Najmabadi, who directs the Center for Energy Research at the University of California at San Diego.
Although commercial fusion power has all these marvelous advantages, there is still one small detail: it doesn’t exist. No one has yet produced an operating fusion plant.
But physicists are cautiously optimistic. “A decade ago, some scientists questioned whether fusion was possible, even in the lab. We now know that fusion will work. The question is whether it is economically practical,” says David E. Baldwin of General Atomics, who oversees one of the largest fusion reactors in the United States, the DIII-D.
NIF—FUSION BY LASER
All this could change rather dramatically in the next few years.
Several approaches are being tried simultaneously, and after decades of false starts, physicists are convinced that they will finally attain fusion. In France, there is the International Thermonuclear Experimental Reactor (ITER), backed by many European nations, the United States, Japan, and others. And in the United States, there is the National Ignition Facility (NIF).
I had a chance to visit the NIF laser fusion machine, and it is a colossal sight. Because of the close connection with hydrogen bombs, the NIF reactor is based at the Lawrence Livermore National Laboratory, where the military designs hydrogen warheads. I had to pass through many layers of security to finally gain access.
But when I reached the reactor, it was a truly awesome experience. I am used to seeing lasers in university laboratories (in fact, one of the largest laser laboratories in New York State is directly beneath my office at the City University of New York), but seeing the NIF facility was overwhelming. It is housed in a ten-story building the size of three football fields, with 192 giant laser beams being fired down a long tunnel. It is the largest laser system in the world, delivering sixty times more energy than any previous one.
After these laser beams are fired down this long tunnel, they eventually hit an array of mirrors that focus each beam onto a tiny pinhead-size target, consisting of deuterium and tritium (two isotopes of hydrogen). Incredibly, 500 trillion watts of laser power are focused onto a tiny pellet that is barely visible to the naked eye, scorching it to 100 million degrees, much hotter than the center of the sun. (The energy of that colossal pulse is equivalent to the output of half a million nuclear power plants in a brief instant.) The surface of this microscopic pellet is quickly vaporized, which unleashes a shock wave that collapses the pellet and unleashes the power of fusion.
It was completed in 2009, and is currently undergoing tests. If all goes well, it may be the first machine to create as much energy as it consumes. Although this machine is not designed to produce commercial electrical power, it is designed to show that laser beams can be focused to heat hydrogen-rich materials and produce net energy.
I talked to one of the directors of the NIF facility, Edward Moses, about his hopes and dreams for his project. Wearing a hard hat, he looked more like a construction worker than a top nuclear physicist in charge of the largest laser lab in the world. He admitted to me that in the past there have been numerous false starts. But this, he believed, was the real thing: he and his team were about to realize an important achievement, one that will enter the history books, the first to peacefully capture the power of the sun on earth. Talking to him, you realize how projects like NIF are kept alive by the passion and energy of their true believers. He savored the day, he told me, when he could invite the president of the United States to this laboratory to announce that history had just been made.
But from the beginning, NIF got off to a bad start. (Even strange things have happened, such as when the previous associate director of NIF, E. Michael Campbell, was forced to resign in 1999 when it was revealed that he lied about completing a Ph.D. at Princeton.) Then the completion date, originally set for 2003, began to slip. Costs ballooned, from $1 billion to $4 billion. It was finally finished in March 2009, six years late.
The devil, they say, is in the details. In laser fusion, for example, these 192 laser beams have to hit the surface of a tiny pellet with utmost precision, so that it implodes evenly. The beams must hit this tiny target to within 30 trillionths of a second of one another. The slightest misalignment of the laser beams or irregularity of the pellet means that the pellet will heat unsymmetrically, causing it to blow out to one side rather than implode spherically.
If the pellet is irregular by more than 50 nanometers (or about 150 atoms), the pellet will also fail to implode evenly. (That is like trying to throw a baseball within the strike zone from a distance of 350 miles.) So alignment of the laser beams and evenness of the pellet are the main problems facing laser fusion.
In addition to NIF, the European Union is backing its own version of laser fusion. The reactor will be built at the High Power Laser Energy Research Facility (HiPER), and it is smaller but perhaps more efficient than NIF. Construction for HiPER starts in 2011.
The hopes of many ride on NIF. However, if laser fusion does not work as expected, there is another, even more advanced proposal for controlled fusion: putting the sun in a bottle.
ITER—FUSION IN A MAGNETIC FIELD
Yet another design is being exploited in France. The International Thermonuclear Experimental Reactor (ITER) uses huge magnetic fields to contain hot hydrogen gas. Instead of using lasers to instantly collapse a tiny pellet of hydrogen-rich material, ITER uses a magnetic field to slowly compress hydrogen gas. The machine looks very much like a huge hollow doughnut made of steel, with magnetic coils surrounding the hole of the doughnut. The magnetic field keeps the hydrogen gas inside the doughnut-shaped chamber from escaping. Then an electrical current is sent surging through the gas, heating it. The combination of squeezing the gas with the magnetic field and sending a current surging through it causes the gas to heat up to many millions of degrees.
The idea of using a “magnetic bottle” to create fusion is not new. It goes back to the 1950s, in fact. But why has it taken so long, with so many delays, to commercialize fusion power?
The problem is that the magnetic field has to be precisely tuned so that the gas is compressed evenly without bulging or becoming irregular. Think of taking a balloon and trying to compress it with your hands so that the balloon is evenly compressed. You will find that the balloon bulges out from the gaps between your hands, making a uniform compression almost impossible. So the problem is instability and is not one of physics but of engineering.
This seems strange, because stars easily compress hydrogen gas, creating the trillions of stars we see in our universe. Nature, it seems, effortlessly creates stars in the heavens, so why can’t we do it on earth? The answer speaks to a simple but profound difference between gravity and electromagnetism.
Gravity, as shown by Newton, is strictly attractive. So in a star, the gravity of the hydrogen gas compresses it evenly into a sphere. (That is why stars and planets are spherical and not cubical or triangular.) But electrical charges come in two types: positive and negative. If one collects a ball of negative charges, they repel each other and scatter in all directions. But if one brings a positive and negative charge together, you get what is called a “dipole,” with a complicated set of electrical field lines resembling a spider web. Similarly, magnetic fields form a dipole; hence squeezing hot gas evenly inside a doughnut-shaped chamber is a fiendishly difficult task. It takes a supercomputer, in fact, to plot the magnetic and electric fields emanating from a simple configuration of electrons.
It all boils down to this. Gravity is attractive and can compress gas evenly into a sphere. Stars can form effortlessly. But electromagnetism is both attractive and repulsive, so gases bulge out in complex ways when compressed, making controlled fusion exceedingly difficult. This is the fundamental problem that has dogged physicists for fifty years.
Until now. Physicists now claim that the ITER has finally worked out the kinks in the stability problem with magnetic confinement.
The ITER is one of the largest international scientific projects ever attempted. The heart of the machine consists of a doughnut-shaped metal chamber. Altogether, it will weigh 23,000 tons, far surpassing the weight of the Eiffel Tower, which weighs only 7,300 tons.
