Finally, Fusion Takes Small Steps Toward Reality

The focus of research on fusion power has moved from big government programs to startups with novel designs.

After three decades of expensive government-funded research that has failed to produce tangible breakthroughs, nuclear fusion has gone from a promising source of effectively limitless power to something more like a punch line.

In the past year, that has started to change, however. Several privately funded companies and small university-based research groups pursuing novel fusion reactor designs have delivered promising results that could shorten the timeline for producing a prototype machine from decades to several years. Commercial power generation from fusion is still a long way off, but the outlines of such a reactor can now be perceived.

Traditional fusion research has centered on large, doughnut-shaped machines called tokamaks, which exert powerful magnetic fields to compress high-temperature plasma—roiling balls of charged particles that fuse to form helium, releasing large amounts of energy in the process. The challenge is to contain the hot plasma and keep it stable; the fusion reactors of today, such as the one at the International Thermonuclear Experimental Reactor (ITER) project in southern France, use giant coils of electromagnets that consume much more energy than the machine actually produces. ITER (pronounced “eater”), which draws scientists and funding from China, the European Union, India, Russia, Japan, South Korea, and the United States, is projected to cost dozens of billions of dollars to produce a working reactor sometime in the 2030s. Maybe.

Two recent developments, offering new and faster pathways to energy-producing fusion reactors, have galvanized the fusion community. Tri Alpha Energy, based in Foothill Ranch, California, said in early August that it has succeeded in keeping a high-energy plasma stable for five milliseconds—much less than the blink of an eye, but “half an eternity” on the scale of fusion reactions, according to chief technology officer Michl Binderbauer.

Tri Alpha, says Binderbauer, is bringing the principles of high-energy particle accelerators, such as the Large Hadron Collider, to bear on the problems of fusion reactors. Specifically, the team has built a device, 23 meters long, that fires two clouds of plasma at each other to form a ring of plasma. The magnetic field that holds the ring together is generated by the plasma itself—a technique known as a field-reversed configuration. The plasma is sustained by the injection of high-energy particles from accelerators.

The challenge for Tri Alpha’s design, says Binderbauer, is “hot enough and long enough”—keeping the plasma stable at a high-enough temperature to achieve energy-positive fusion. The recent experiment indicated that the company—which has attracted millions of dollars in funding from investors including Goldman Sachs and Vulcan, the investment fund of Microsoft cofounder Paul Allen—has solved the long-enough problem. Making the plasma hot enough is the next key challenge. Next year, Tri Alpha will begin building a new and more powerful version of its experimental device to test the process at higher temperatures.

At MIT’s Plasma Science and Fusion Center, a group headed by Dennis Whyte, a professor of nuclear science and engineering and the center’s director, and graduate student Brandon Sorbom published a conceptual design in July for a machine called the ARC reactor (“affordable, robust, compact”). The novelty of the ARC design is the nature of the electromagnets that confine the plasma. Using recently developed, flexible superconducting tapes made of rare-earth barium copper oxide, the ARC reactor can achieve magnetic fields with much higher amplitude—thus enabling a reactor design much smaller than other tokamak-based machines. The researchers also envision a liquid “blanket” surrounding the plasma that will absorb neutrons without damage and provide an efficient heat-exchange medium to produce electricity.

Increasing the amplitude of the surrounding magnetic field raises the amount of fusion power produced in the plasma to the fourth power—a dramatic increase that could lead to a commercial prototype in a matter of years, according to Whyte.

“It’s well known that you can make very compact devices if you raise the magnetic field to very high levels,” he says, “but the electromagnets had to be copper—no superconductor could tolerate that magnetic field.” Now the advent of advanced superconductor tapes could enable a compact reactor that produces fusion continuously.

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