How Fusion Works and Why It’s a Breakthrough American science scores a triumph, though it’ll be decades before it yields a viable energy source. By Steven E. Koonin and Robert L. Powell
The Energy Department has announced the first gain in energy from fusion in a laboratory—the first time fusion reactions produced more energy than it took to induce them. Last week 192 laser beams at the Lawrence Livermore Laboratory’s National Ignition Facility heated and compressed a capsule of hydrogen to previously unattainable temperatures and pressures, igniting fusion reactions that produced 50% more energy than the laser beams had delivered.
Nuclear reactions can release the energy that binds together protons and neutrons in an atom’s nucleus. Nuclear power plants use fission, not fusion. Fission releases energy when a large uranium nucleus splits into two radioactive fragments, which carry the energy as they fly apart.
Fusion, by contrast, relies on the universe’s smallest atom, hydrogen. Energy is released when two hydrogen nuclei combine to produce a helium nucleus and a neutron. Unlike fission, fusion produces no radioactive fragments. Fusion is much harder to induce than fission, since the hydrogen nuclei must be heated to nearly 100 million degrees Celsius to overcome the electrical repulsion that hinders their reaction. Stars run on fusion energy, but on Earth it has previously been released only in thermonuclear explosions. This stunning new result in laboratory fusion opens doors for unprecedented studies in basic and applied science.
The concept of laser fusion had been pursued without success since the 1960s and it became a central part of a 1990s program to ensure continued confidence in the nuclear-weapons stockpile without underground testing. Although scientists knew that high-powered laser beams could probe the properties of matter relevant to the early stages of detonating a nuclear weapon, the goal of laser fusion would allow for studies in the later stages. It would also challenge and demonstrate the ability to understand and predict the dynamics of hot, dense matter more generally.
Construction of the ignition facility at the Livermore lab began in 1997, and experiments attempting ignition began soon after construction was completed in 2009. The design and construction of the world’s most powerful laser was an engineering triumph, but three years of failed attempts to achieve fusion ignition brought the program close to cancellation in 2012. But the program continued with a more deliberate approach that included outside peer review.
The decade of research from 2012 to 2022 illustrated the ability of the Energy Department’s national laboratories to marshal an interdisciplinary team of scientific and engineering talent from the government, universities and private sector in long-term pursuit of an audacious goal. Researchers in lasers, nuclear and plasma physics, precision-target fabrication, instrumentation and high-fidelity computer modeling helped design and undertake a series of experiments that gradually approached ignition conditions. The payoff came last week.
As recent world events make apparent, the U.S. nuclear deterrent is effective only if there’s confidence that the weapons remain effective. Laser ignition demonstrates to the world a deep understanding of weapons science and will be important in sustaining confidence in the coming decades.
The U.S. hasn’t been alone in recognizing the importance of laser fusion. France and China are building comparable facilities. But as the new American results show, the years of learning were necessary to form a potent intellectual and innovation ecosystem at the National Ignition Facility. The U.S. now leads every other country by a decade because of its foresight, perseverance and research enterprise. Continued investment in laser fusion will ensure that this leadership endures.
These days one can’t mention fusion without thinking about energy. The ignition milestone demonstrates fusion gain, a necessary condition for practical energy production. But that is only the first step. Several decades of engineering would be required to make fusion a practical, emissions-free source of electricity. And even then, it would have to be cost-competitive with alternatives. Like the initial decision to pursue the ignition goal, this is not at all guaranteed. But it’s well worth considering.
Mr. Koonin is a professor at New York University, a senior fellow at the Hoover Institution and author of “Unsettled: What Climate Science Tells Us, What It Doesn’t, and Why It Matters.” Mr. Powell is a professor at the University of California, Davis. Both are governors of Lawrence Livermore National Laboratory.
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