The most ambitious clean energy option — fusion, a lesser-known type of nuclear power that could one day put a near-limitless supply of electricity on the grid — has faced one big problem for years: It's expensive.

The research is expensive. The logistics are expensive. The materials are expensive. But that might be changing,—thanks to scientists who are figuring out how to tweak complex magnetic fields.

A recent paper published in Nature Physics chronicles how a team of scientists working at KSTAR in South Korea figured out how to predict and calm down explosive bursts called “edge-localized modes.” Left wild, these modes can get big enough to cause permanent damage to the reactor.

“It was a big surprise to everybody,” first author Jong-Kyu Park, a researcher at the Princeton Plasma Physics Laboratory (PPPL), told The Daily Beast. “When we validated this method with such high accuracy, it was really unprecedented.”

Park said the future of fusion power — which hangs on the highly-anticipated International Thermonuclear Experimental Reactor (ITER) under construction in France — depends on this ability to control these solar flare-like bursts of energy.

A reactor is, after all, essentially an artificial star. Like the sun, it runs on continuous fusion reactions fueled by plasma, a super high-energy, charged gas that can run up to 200 million degrees Celsius. This plasma on earth can erupt in in fast, filament-like bursts of energy, just like solar flares. They're notoriously unstable. That's bad news for any potential buyer of a fusion reactor: damage requires maintenance.

“It's absolutely necessary. We believe so,” Park said. “Because otherwise, this instability in the edge region can damage plasma-facing components or the vessels that confine plasmas. [...] So in order to make a successful fusion reactor, we really have to invent a way to control those instabilities.”

The secret to controlling these bursts turned out to be a series of complex magnetic fields. It's a big deal, Park said, because the team couldn't take the easier route: the predictable symmetry in magnetic fields other scientists had used before. The only way the team could convince the plasma to simmer down, so to speak, was to use a non-symmetrical type of magnetic field in 3-D space.

The math was complex. These fields weren't symmetric: they were off the grid. Other scientists heralded the achievement — using jargon, of course.

“Experiments have now proven that optimized non-axisymmetric magnetic fields can provide much improved control without degrading the plasma confinement,” Columbia University physics professor Allen Boozer (who wasn’t involved in the research) wrote in a commentary featured in the same issue of Nature Physics.

In plain English: The scientists used these complex magnetic fields to control the plasma.

The stakes are high: Experts say the switch to fusion could generate enough electricity to slow climate change and improve lives worldwide. In his end-of-2018 letter, Bill Gates urged U.S. leaders to "get into the game”: to take advanced nuclear energy seriously by funding projects and focusing on updating regulations.

Unlike oil, natural gas, and coal, fusion runs on fuel that is essentially limitless. It's just two forms (isotopes) of hydrogen: deuterium and tritium. Fusion fuel is also quite efficient: One kilogram of it can make as much energy as 10 million kilograms of fossil fuel.

AND it produces no greenhouse gas emissions. Its main byproduct is helium, a non-toxic gas that doesn't contribute to air pollution. Even that could be recycled: According to the EUROfusion consortium, a fusion power plant might be able to convert the leftover helium into its liquid form, which could be re-used to cool the magnets.

Fusion is also far safer than fission, the other nuclear energy with a bad reputation. Whereas a fission plant works by splitting heavy elements like uranium apart, a fusion plant produces energy by bringing super light things together. Fusion, unlike fission, doesn't require plutonium. Its waste isn't radioactive. Even the plant itself is far less radioactive: in a paper published in Nuclear Fusion , researchers calculated that 100 years after a fusion reactor is shut down, its level of radioactivity will be about one-millionth of the radioactivity in a fission reactor of the same power.

Still, the economics are complicated and difficult to predict.

“ Now, we are very confident we can use [the 3-D fields], and they can produce big benefits. ” — Jong-Kyu Park,Princeton Plasma Physics Laboratory

According to a report from the Lawrence Livermore National Laboratory in California, these edge-localized modes' (ELM) power fluxes cause plasma to lose up to 10 percent of its energy inside a reactor. Another team working with data from the Joint European Torus (JET), a tokamak reactor in Oxfordshire, UK, estimated ELMs create an energy loss anywhere from 2 percent to 10 percent. (JET has already produced 16 megawatts of fusion power using deuterium and tritium fuels.)

The paper notes that “full surface melting may not ultimately set the final limit on tolerable ELM sizes in ITER” — that is, there's only so much these plasma-facing components can handle. Tungsten will do much of the heavy lifting. But like any material, it's imperfect.

Amitava Bhattacharjee, head of theory at the PPPL, recently led a Simulations of Disruptions workshop that convened 35 scientists from around the world. By the time ITER is up and running, scientists will need to know exactly how the plasma will behave, he said. The goal is to prevent disruptions, or at least mitigate damage when it happens.

Park says the team expects to apply this method to future tokamaks, including ITER.

“Now, we are very confident we can use [the 3-D fields], and they can produce big benefits,” he said.

The reactor, which aims to show how fusion could work on a commercial scale, is slated to—at long last—finish construction next year. ITER will begin experiments in 2025 or so, and the earliest launch of a 500 megawatt fusion power plant is likely 2055.