How Los Alamos is Helping Ready Nuclear Fusion Power for the Grid by 2030

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As the saying goes, fusion power has been 20 years away for the past 50 years. But technological momentum is now accelerating. In 2022, the Biden Administration declared a national goal of getting fusion energy onto the grid by the 2030s, and since then, around 6.2 billion dollars in global investments have poured into the effort to turn fusion’s promise into a reality. In tokamak reactors—the human-made stars being developed for power production—the hydrogen contained within the 16 gallons of water used in a typical shower should be able to generate the same amount of energy as 8 tons of burned coal. As the technology nears maturity, problems associated with heating particles to 150 million °C, ten times the temperature in the Sun’s core, keep arising. Michael Lively, a Lab engineer and fusion expert who specializes in modeling solutions to these problems, may have solved one key issue.

Fusion reactors work by extracting tremendous sums of energy from the fusion of lighter atomic nuclei into a heavier nucleus. The process, essentially the opposite of the atom-splitting fission process that powers nuclear weapons and reactors, could produce more energy and far less waste than its fission cousin. In the International Thermonuclear Experimental Reactor, or ITER, a flagship fusion reactor under construction in France, the extreme temperatures and pressures needed to fuse atoms are achieved with a very fancy machine that features 100,000 kilometers of superconducting wire and 10,000-pound magnets chilled to temperatures colder than Pluto. Inside the donut-shaped reactor, these giant magnets accelerate a current of electrons, charged particles, and hydrogen isotopes until they form a plasma. When the plasma reaches 100 million °C, the nuclei of light hydrogen atoms can fuse, releasing astronomical sums of energy through the same process that fuels stars. But instability breeds in extreme conditions. The plasma is wildly unruly and often tries to escape the reactor. “Loss of confinement is probable, perhaps even inevitable,” Lively says. 

One severe byproduct of this instability is runaway electrons. Under normal operating conditions, the plasma current is carried by the magnets’ interaction with the electrons. But under certain conditions caused by factors ranging from mechanical vibrations to small imperfections in the magnetic field, sudden and violent instabilities can superheat a small population of electrons to hotter than the plasma itself. These supra-thermal electrons, the runaways, begin to drive the current. Initially, they follow the lines of the reactor’s internal magnetic fields, but during disruption events, those magnetic lines can shift, driving a beam of 100-million °C plasma into a small patch of the reactor’s tungsten wall. “It isn’t damage over time,” says Lively. “In one event, the beam can punch a hole in a solid tungsten wall, damaging the subsurface cooling mechanism beneath.” And costing untold dollars in lost power generation, time, and repairs.

Lively’s idea to mitigate this damage relies on what he calls a tungsten shotgun. Tungsten is one of the strongest naturally occurring metals, which is why engineers use it in reactor walls. Lively’s shotgun would inject into the reactor a spray of millimeter-wide tungsten particles to intercept the runaway electrons. To model the electron-tungsten particle interaction, Lively used MCNP, a general-purpose radiation transport code developed at the Lab in the late-1970s. He represented particle trajectories, energy loss and deposition, and the secondary radiation that occurs when high-energy runaway electrons strike tungsten particles in a tokamak reactor. The initial findings were promising. “The runaway beam is effectively terminated, near instantaneously,” he says.

According to Lively’s results, when the runaways collide with the tungsten particles, all but a very small amount of their energy is removed. The tungsten absorbs 8 percent of the runaway electrons, while the remaining 92 percent is bounced or scattered out of orbit and beyond the risk of damaging the reactor. Lively found that runaways tend to orbit the reactor for just 130 nanoseconds while the tungsten particles have a lifespan of 100,000 nanoseconds. Practically speaking, this discrepancy means the tungsten particles could be blasted into the reactor as soon as runaway electrons are sensed. The particles would remain in the machine for long enough to protect it from all but the most extreme of these, so far, unpreventable runaway events. 

“The upshot is pretty simple,” Lively says. “We should be able to protect nuclear fusion reactors from loss of plasma control without component damage or downtime for expensive repairs. And we can do so with little to no economic impact.” The next step, he adds, is implementing the design.

People also ask

• What is nuclear fusion? How is it different from nuclear fission? Nuclear fusion is often hailed as the holy grail of energy sources: a clean, renewable technology that replicates the process powering the sun and stars. A single reactor could deliver 500 megawatts to the grid, matching the output of a large coal power plant. Unlike nuclear fission, which splits atoms apart in a dramatic energy release (think reactors or nuclear weapons), fusion generates power by merging lighter atoms—like hydrogen—into heavier ones, like helium. This process occurs under immense pressure and heat in experimental reactors, such as the ITER reactor in southern France, releasing massive energy with less radioactive waste. But many scientific challenges remain before fusion can be operational. 
• What is Los Alamos National Laboratory doing to advance this potentially game-changing clean energy technology? Enter Los Alamos National Laboratory, where brilliant minds are working tirelessly to make fusion energy a reality on Earth. Through collaborations with Lawrence Livermore National Laboratory and other national labs, our scientists are enhancing tokamak fusion reactors—devices that effectively create controlled miniature stars—to bring fusion from the experimental stage to the grid. By addressing hurdles like containing super-hot plasma and controlling runaway electrons, Los Alamos is breaking new scientific ground on a future fueled by nearly unlimited, clean energy.