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Sustainable Energy

Top Fusion Experiments

We review some of the attempts to contain ultrahot plasmas and create tiny stars on earth.

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Fusion is the mythical beast of energy technologies—the one that could solve all of our energy problems by providing a nearly limitless source of power, but one that forever seems to be decades away from reality. Yet scientists have made real progress toward using fusion as an energy source, and along the way they’ve built fascinating machines, including the world’s most powerful lasers and sculpture-like magnetic coils capable of confining 100,000,000 ºC plasmas. Here are some of the most interesting projects, ranging from some of the first attempts to today’s cutting-edge efforts.

Devices called mirror magnets for confining the ultrahot plasmas needed for fusion were first built by researchers at Lawrence Livermore Laboratory in the 1950s. In the 1960s, they developed mirror magnets shaped like the seams on a baseball. The second version (shown) was built in 1969. The shape of the magnet created a weak magnetic field surrounded by a strong magnetic field to confine the plasma. The magnetic field produced was roughly 1,500 times stronger than a typical refrigerator magnet.

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Livermore researchers introduced successively larger mirror magnet machines to improve plasma confinement. This photo, from 1981, shows workers moving a 420-ton magnet into place at one end of the Mirror Fusion Test Facility. It was designed to help confine plasma up to nearly 500,000,000 ºC.

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While developing mirror magnets, Livermore researchers also developed extremely powerful lasers that would converge on a capsule of hydrogen at the center of a sphere. Livermore’s lasers were used to simulate fusion in nuclear weapons and to develop new electricity-generation methods.  In 1977, the laser directed at this sphere, called Shiva, was the world’s most powerful laser.

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In 1984, Livermore upgraded to the Nova laser, which featured 20 laser beams that converged on a target hydrogen capsule. The facility was featured in the original Tron movie.

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In 2008, Governor Arnold Schwarzenegger visited the most recent iteration of the fusion laser system at Livermore, the National Ignition Facility. It focuses 192 lasers on the target with the goal of igniting a short-lived but self-sustaining fusion reaction—essentially a tiny star. To generate electricity, a system like this would have to fire a laser many times per minute to generate sustained heat.

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Technicians examine the inside of the National Ignition Facility. The cone projecting into the center will hold a capsule the size of a pencil eraser that contains hydrogen isotopes.

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One common type of fusion experiment uses magnets and an electrical current to confine plasma. One version of these so-called tokamak devices was constructed at the Princeton Plasma Physics Laboratory, shown here in 2009. This one uses a wall of liquid lithium to improve the stability of the plasma.

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The Princeton Plasma Physics Lab also worked on another type of magnetic plasma confinement called the stellarator. This approach used computer models to design elaborately shaped magnetic coils, eliminating the need for an electrical current to help stabilize the field, and possibly leading to more stable plasma confinement. This photo, from November 2007, shows a technician assembling one of the coils. The Princeton stellarator was canceled due to cost overruns.

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The Iter project in southern France is building the world’s largest tokamak. Construction is underway on a 250-meter-long facility (shown) dedicated to winding the coils needed for one of the types of magnets used to confine the plasma.

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