National Ignition Facility became one step closer to the holy grail of clean energy: fusion.....

February 21, 2022

The path to create fusion—the type of nuclear reaction that powers the sun and stars—has a long history, involving some of the greatest minds in physics. British astrophysicist Arthur Eddington first conceived of fusion, and, in 1925, he published a seminal paper theorizing that stars fuse hydrogen into helium. Nuclear physicist Hans Bethe advanced the science, and from there, physicists Enrico Fermi and Edward Teller used fusion to create a thermonuclear bomb.

Yet, the “holy grail” of fusion, according to Los Alamos National Laboratory postdoc James Sadler, is to use fusion as an energy source that would emit no pollution, last almost indefinitely, and result in little or zero waste. Sadler and Hui Li, both of the Lab’s Nuclear and Particle Physics, Astrophysics and Cosmology group, have been working to better understand how this might be achieved.

To replicate the environment of the sun, the National Ignition Facility (NIF), at California’s Lawrence Livermore National Laboratory, uses lasers—lots of them. In a lab the size of three football fields, 192 lasers are amplified, reflected, and focused into a point. These beams can generate temperatures of more than 180 million degrees Fahrenheit and the pressure of 100 billion Earth atmospheres. Their target is a small capsule the size of a pencil eraser, filled with hydrogen gas.

Under intense pressure and heat from the lasers, the electrons surrounding hydrogen gas break their atomic bonds and become a plasma. Deuterium and tritium nucleons (both isotopes of hydrogen) fuse to form energetic helium, which share its energy with more deuterium and tritium, driving a self-sustained reaction, called ignition.

Ignition, however, has not yet been achieved. One major hurdle is that as electrons move about the confined capsule, they take energy from hotter regions and share it with cooler regions, which reduces the overall temperature and slows the reaction. To prevent this sharing of energy, researchers have applied external magnetic B-fields to the capsules, hoping to contain the roaming electrons in a super-heated pocket.

Sadler and Li, however, believe that perhaps those external magnetic fields are unnecessary. They discovered that the fusion process spontaneously creates its own, self-generated magnetic fields. These alone might be powerful enough to insulate the electrons from sharing their energy, though the researchers cannot say for certain yet because the simulation codes used by national labs to model the behavior of fusion at NIF don’t account for self-generated fields.

“We don’t know if these fields should be a high priority concern,” Li says. “So what we’re doing is introducing these fields into our models to see how they change the parameters of ignition. If we learn they’re a low priority, they will at least make our models more accurate. If we learn they’re a high priority, reaching ignition may be easier than we think.”

Shortly after Li spoke with NSS magazine, in August 2021, NIF almost reached ignition. What happened? Sadler and Li suspect that the self-generated magnetic fields they discovered reduced heat loss between electrons by 10 percent or more, enhancing the energy yield by more than a factor of three.

That being said, Li realizes many variables—such as temperature, how long the lasers are active, and alterations to the capsules that hold the tritium and deuterium—may have also contributed to the August results. Scientists at NIF and Los Alamos will be analyzing the data for years to come. But the near-success is a good indication that, for the first time, humans may be on the threshold of creating fusion power.

“The moment you can generate fusion,” Sadler says, “it can be used for many things: to learn how stars form and live, to produce an intense neutron source, and ultimately, to create a clean energy source.”

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