Los Alamos National Lab blasts runaway electrons with tungsten particles to prevent fusion damage.

Harnessing the energy of stars is no simple feat – scientists have been "20 years away" from the successful attainment of sustained nuclear fusion for more than five decades. A Los Alamos National Laboratory discovery that utilizes a "tungsten shotgun" to neutralize destructive instability in fusion reactors may be the key to finally hitting that moving target, bringing the promise of limitless clean power closer to reality.

For decades, fusion has been the most ambitious energy pursuit for humanity, a scientific challenge of cosmic proportions. In 2021, the National Ignition Facility achieved the unthinkable by replicating the thermonuclear reactions that fuel stars, for a brief moment producing energy levels never before seen on Earth.

By 2022, the facility broke another barrier, surpassing energy breakeven – producing more energy from a fusion reaction than was required to ignite it – a milestone many thought impossible.

These groundbreaking successes have reignited momentum across the scientific community, propelling efforts like those at Los Alamos National Laboratory to tackle the final obstacles in turning fusion's limitless potential into a global reality.

Unlike fission, which splits atoms to release energy, fusion merges lighter atoms to form heavier ones, producing significantly more energy with minimal waste. This process, the same that powers stars, requires extraordinary conditions to achieve.

The International Thermonuclear Experimental Reactor (ITER) in France offers a glimpse into these challenges. Using magnets chilled to temperatures colder than Pluto, ITER accelerates particles into a plasma heated to more than 100 million degrees Celsius (180 million degrees Fahrenheit).

At these extremes, hydrogen atoms fuse, releasing enormous energy; yet managing this plasma is one of fusion's greatest technical hurdles, as its behavior can be unpredictable and requires science that dares to venture where no one has gone before to maintain stability and hold the power of a star.

"Loss of confinement is probable, perhaps even inevitable," said Michael Lively, a lab engineer and fusion expert at Los Alamos National Laboratory, highlighting the challenges posed by runaway electrons – high-energy particles that can wreak havoc on reactor walls if left unchecked.

Within fusion reactors, the extreme conditions can trigger a dangerous phenomenon known as runaway electrons. These high-energy particles arise when small disturbances – like mechanical vibrations or imperfections in the magnetic field – disrupt the plasma's stability.

A fraction of electrons can become superheated to temperatures far exceeding the plasma itself, escaping confinement and striking the reactor's tungsten walls, with a single impact capable of punching through solid metal, damaging the cooling systems beneath, and bringing power generation to a costly halt.

To confront this volatile phenomenon, Lively has proposed what he calls a "tungsten shotgun," a solution that utilizes one of the strongest naturally occurring metals to shield reactors from potentially catastrophic energy bursts.

Already a critical material in reactor walls for its resilience, tungsten is at the heart of this approach, which involves injecting a spray of millimeter-wide particles into the reactor to intercept runaway electrons.

Using Monte Carlo N-Particle (MCNP), a radiation transport code developed at Los Alamos in the late 1970s to simulate interactions between radiation and matter, Lively modeled how tungsten particles interact with high-energy electrons.

These simulations calculated particle trajectories, energy loss, and the secondary radiation produced when electrons collide with the tungsten particles.

"The runaway beam is effectively terminated, near instantaneously," Lively said.

These results revealed that tungsten particles are highly effective at neutralizing runaway electrons. When the particles collide with the runaways, 8% of the electrons' energy is absorbed by the tungsten, while the remaining 92% is scattered safely out of orbit, beyond the risk of damaging the reactor.

Timing is paramount; Lively found that runaway electrons orbit the reactor for just 130 nanoseconds, while tungsten particles remain active for 100,000 nanoseconds. This significant lifespan difference means the tungsten particles can be injected into the reactor as soon as runaway electrons are detected, providing sufficient time to mitigate all but the most extreme events.

"The upshot is pretty simple," Lively explained. "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."

While the tungsten shotgun offers a promising path forward, its success depends on further testing and implementation. As fusion research continues to advance, innovations like this may play a critical role in unlocking the potential of limitless clean energy, bringing humanity one step closer to harnessing the power of the stars.