by Michio Kaku
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.
(photo credit 5.1)
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.
Two types of fusion. On the left, lasers compress a pellet of hydrogen-rich materials. On the right, magnetic fields compress a gas containing hydrogen. By midcentury, the world may derive its energy from fusion. (photo credit 5.2)
The components are so heavy that the roads transporting the equipment have to be specially modified. A large convoy of trucks will transport the components, with the heaviest weighing 900 tons and the tallest being four stories high. The ITER building will be nineteen stories tall and sit on a huge platform the size of sixty soccer fields. It is projected to cost 10 billion euros, a cost shared by seven member states (the European Union, the United States, China, India, Japan, Korea, and Russia).
When it is finally fired up, it will heat hydrogen gas to 270 million degrees Fahrenheit, far surpassing the 27 million degrees Fahrenheit found in the center of the sun. If all goes well, it will generate 500 megawatts of energy, which is ten times the amount of energy originally going into the reactor. (The current record for fusion power is 16 megawatts, created by the European JET (Joint European Torus) reactor at the Culham Science Center, in Oxfordshire, UK.) After some delays, the target date for break-even is now set to be 2019.
The ITER is still just a science project. It is not designed to produce commercial power. But physicists already are laying the groundwork for the next step, taking fusion power to the marketplace. Farrokh Najmabadi, who leads a working group looking into commercial designs for fusion plants, has proposed ARIES-AT, a smaller machine than the ITER, which would produce a billion watts at roughly 5 cents per kilowatt-hour, making it competitive with fossil fuels. But even Najmabadi, who is optimistic about fusion, admits that fusion won’t be ready for widespread commercialization until the middle of the century.
Another commercial design is the DEMO fusion reactor. While the ITER is designed to produce 500 megawatts for a minimum of 500 seconds, the DEMO will be designed to produce energy continually. The DEMO adds one extra step lacking in the ITER. When fusion takes place, an extra neutron is formed, which quickly escapes from the chamber. However, it is possible to surround the chamber with a special coating, called the blanket, specifically designed to absorb the energy of this neutron. The blanket then heats up. Pipes inside the blanket carry water, which then boils. This steam is sent against the blades of a turbine that generates electricity.
If all goes well, the DEMO will go online in 2033. It will be 15 percent larger than the ITER reactor. DEMO will produce twenty-five times more energy than it consumes. Altogether, DEMO is expected to produce 2 billion watts of power, making it comparable to a conventional power plant. If the DEMO plant is successful, it could lead to rapid commercialization of this technology.
But many uncertainties remain. The ITER reactor has already secured the funding necessary for construction. But since the DEMO reactor is still in its planning stages, delays are to be expected.
Fusion scientists believe that they have finally turned the corner. After decades of overstatements and failures, they believe that fusion is within grasp. Not one but two designs (NIF and ITER) may eventually bring fusion electricity into the living room. But since neither NIF nor ITER is yet delivering commercial fusion power, there is still room for the unexpected, such as tabletop fusion and bubble fusion.
TABLETOP FUSION
In the final scene in the movie Back to the Future, Doc Brown, the crazy scientist, is seen scrambling to get fuel for his DeLorean time machine. Instead of fueling up with gasoline, he searches garbage cans for banana peels and trash and then dumps everything into a small canister called Mr. Fusion.
Given a hundred years, is it possible that some breakout design may reduce huge football field–size machines to the size of a coffeemaker, like in the movie?
One serious possibility for tabletop fusion is called sonoluminescence, which uses the sudden collapses of bubbles to unleash blistering temperatures. It is sometimes called sonic fusion or bubble fusion. This curious effect has been known for decades, going back to 1934, when scientists at the University of Cologne were experimenting with ultrasound and photographic film, hoping to speed up the development process. They noticed tiny dots in the film, caused by flashes of light generated by the ultrasound creating bubbles in the fluid. Later, the Nazis noticed that bubbles emitted from their propeller blades often glowed, indicating that high temperatures were somehow being produced inside the bubbles.
Later, it was shown that these bubbles were glowing brightly because they collapsed evenly, thereby compressing the air in the bubble to enormously high temperatures. Hot fusion, as we saw earlier, is plagued by the uneven compression of hydrogen, either because laser beams striking the pellet of fuel are misaligned or the gas is being squeezed unevenly. As a bubble shrinks, the motion of the molecules is so rapid that air pressure inside the bubble quickly becomes uniform along the bubble walls. In principle, if one can collapse a bubble under such perfect conditions, one might attain fusion.
Sonoluminescence experiments have successfully produced temperatures of tens of thousands of degrees. Using noble gases, one can increase the intensity of light emitted from these bubbles. But there is some controversy over whether it can achieve temperatures hot enough to produce nuclear fusion. The controversy stems from the work of Rusi Taleyarkhan, formerly of the Oak Ridge National Laboratory, who claimed in 2002 that he was able to achieve fusion with his sonic fusion device. He claimed to have detected neutrons from his experiment, a sure sign that nuclear fusion was taking place. However, after years of work by other researchers who have failed to reproduce his work, this result, for the moment, has been discredited.
Yet another wild card is the fusion machine of Philo Farnsworth, the unsung coinventor of TV. As a child, Farnsworth originally got the idea for TV by thinking of the way a farmer plows his fields, row after row. He even sketched the details of his prototype at the age of fourteen. He was the first to transfer this idea to a fully electronic device capable of capturing moving images on a screen. Unfortunately, he was unable to capitalize on his landmark invention and was mired in lengthy, messy patent fights with RCA. His legal battles even drove him crazy, and he voluntarily checked himself into an insane asylum. His pioneering work on TV went largely unnoticed.
Later in life, he turned his attention to the fusor, a small tabletop device that can actually generate neutrons via fusion. It consists of two large spheres, one inside the other, each made of a wire mesh. The outer mesh is positively charged, while the inner mesh is negatively charged, so protons injected through this mesh are repelled by the outer mesh and attracted to the inner mesh. The protons then smash into a hydrogen-rich pellet in the middle, creating fusion and a burst of neutrons.
The design is so simple that even high school students have done what Richter, Pons, and Fleischmann could not do: successfully generate neutrons. However, it is unlikely that this device will ever yield usable energy. The number of protons that are accelerated is extremely small, and hence the energy resulting from this device is very tiny.
In fact, it is also possible to produce fusion on a tabletop using a standard atom smasher or particle accelerator. An atom smasher is more complicated than a fusor, but it can also be used to accelerate protons so that they can slam into a hydrogen-rich target and create fusion. But again, the number of protons that are fused is so small that this is an impractical device. So both the fusor and atom smasher can attain fusion, but they are simply too inefficient and their beams are too thin to produce usable power.
Given the enormous stakes, no doubt other enterprising scientists and engineers will have their chance to turn their basement contraptions into the next mega invention.
AGE OF MAGNETISM
The previous century was the age of electricity. Because electrons are so easily manipulated, this has opened up entirely new technologies, making possible radio, TV, computers, lasers, MRI scans, etc. But sometime in this century, it is likely that physicists will find their holy grail: room temperature superconductors. This will usher in an entirely new era, the age of magnetism.
Imagine riding in a magnetic car, hovering above the ground and traveling at several hundred miles per hour, using almost no fuel. Imagine trains and even people traveling in the air, floating on magnetism.
We forget that most of the gasoline we use in our cars goes to overcoming friction. In principle, it takes almost no energy to ride from San Francisco to New York City. The main reason this trip consumes hundreds of dollars of gasoline is because you have to overcome the friction of the wheels on the road and the friction of the air. But if you could somehow cover the road from San Francisco to New York with a layer of ice, you could simply coast most of the way almost for free. Likewise, our space probes can soar beyond Pluto with only a few quarts of fuel because they coast through the vacuum of space. In the same way, a magnetic car would float above the ground; you simply blow on the car, and the car begins to move.
The key to this technology is superconductors. It has been known since 1911 that mercury, when cooled to four degrees (Kelvin) above absolute zero, loses all electrical resistance. This means that superconducting wires have no energy loss whatsoever, since they lack any resistance. (This is because electrons moving through a wire lose energy as they collide with atoms. But at near absolute zero, these atoms are almost at rest, so the electrons can easily slip through them without losing energy.)
These superconductors have strange but marvelous properties, but one severe disadvantage is that you have to cool them to near absolute zero with liquid hydrogen, which is very expensive.
Therefore, physicists were in shock in 1986 when it was announced that a new class of superconductors had been found that did not need to be cooled to these fantastically low temperatures. Unlike previous materials like mercury or lead, these superconductors were ceramics, previously thought to be unlikely candidates for superconductors, and became superconductors at 92 degrees (Kelvin) above absolute zero. Embarrassingly, they became superconductors at a temperature that was thought to be theoretically impossible.
So far, the world record for these new ceramic superconductors is 138 degrees (Kelvin) above absolute zero (or -211° F). This is significant, since liquid nitrogen (which costs as little as milk) forms at 77° K (-321° F) and hence can be used to cool these ceramics. This fact alone has drastically cut the costs of superconductors. So these high-temperature superconductors have immediate practical applications.
But these ceramic superconductors have just whetted the appetite of physicists. They are a giant step in the right direction, but still they are not enough. First, although liquid nitrogen is relatively cheap, you still have to have some refrigeration equipment to cool the nitrogen. Second, these ceramics are difficult to mold into wires. Third, physicists are still bewildered by the nature of these ceramics. After several decades, physicists are not quite sure how they work. The quantum theory of these ceramics is too complicated to solve
at the present time, so no one knows why they become superconductors. Physicists are clueless. There is a Nobel Prize waiting for the enterprising individual who can explain these high-temperature superconductors.
But every physicist knows the tremendous impact that a room temperature superconductor would have. It could set off another industrial revolution. Room temperature superconductors would not require any refrigeration equipment, so they could create permanent magnetic fields of enormous power.
For example, if electricity is flowing inside a copper loop, its energy dissipates within a fraction of a second because of the resistance of the wire. However, experiments have shown that electricity within a superconducting loop can remain constant for years at a time. The experimental evidence points to a lifetime of 100,000 years for currents inside a superconducting coil. Some theories maintain that the maximum limit for such an electrical current in a superconductor is the lifetime of the known universe itself.
At the very least, such superconductors could reduce the waste found in high-voltage electrical cables, thereby reducing the cost of electricity. One of the reasons an electrical plant has to be so close to a city is because of losses in the transmission lines. That is why nuclear power plants are so close to cities, which poses a health hazard, and why wind power plants cannot be placed in areas with the maximum wind.
