Newsweek By Hannah Osborne On 6/22/17
The prospect of fusion energy—a potentially limitless and clean source of power—has just edged a little closer. Scientists believe they have solved a fundamental problem with building reactors that produce fusion power.
Nuclear fusion produces energy in the same way as the sun and stars, combining lightweight atomic nuclei by using high pressures and temperatures of around 150 million degrees Celsius (270 million degrees Fahrenheit) hotter than the center of the sun. It can be created using hydrogen isotopes, such as deuterium, which can be extracted easily from seawater, meaning the fuel is almost inexhaustible.
The reaction that takes place when lighter elements join together to create heavier ones produces energy, creating plasma—a state of matter—in the process. The reactor where this takes place must somehow confine and suspend the superheated plasma produced without it touching (and therefore damaging) the walls.
Currently, scientists are working on reactors that control the plasma through magnets, but so far fusion reactors have not produced more energy than they take to run in the first place.
On top of this, there is another problem: runaway electrons produced in the reaction. These are electrons with extremely high energy that suddenly accelerate, potentially damaging the reactor wall in the process. Researchers at the Chalmers University of Technology, Sweden, have now found a way to solve this issue.
In a study published in the journal Physical Review Letters, they have outlined a model to slow down the electrons, meaning they become harmless to the reactor.
At present there are two types of fusion reactors, the tokamak and the stellarator. Both use similar principles to harness the plasma with magnets in a doughnut-shaped reactor. In the study, plasma physicists Linnea Hesslow and Ola Embréus were looking at tokamaks and the unwanted electrical fields runaway electrons produce.
The team managed to slow the runaway electrons by injecting heavy ions into them. When the electrons collide with the nuclei of the ions, the resistance they encounter makes them lose speed. More and more collisions means the electrons’ speed is slowed down to the point where it is controllable, meaning the production of fusion energy can continue.
“When we can effectively decelerate runaway electrons, we are one step closer to a functional fusion reactor,” Hesslow said in a statement. “Considering there are so few options for solving the world’s growing energy needs in a sustainable way, fusion energy is incredibly exciting since it takes its fuel from ordinary seawater.”
There are still huge challenges when it comes to producing fusion energy—the main one being achieving the temperatures required. At the moment, the energy needed to reach over 100 million degrees Celsius (180 million degrees Fahrenheit) vastly outweighs what the reaction would produce in return.
However, there are other technical problems when it comes to making a reactor, Hesslow tells Newsweek. “The control of runaways is one of a range of challenges, including materials development for the wall and exhaust regions, which must be tackled in the development of fusion energy,” she says in an email interview.
Scientists have been working on achieving fusion for over 50 years, and physicists often say the technology required is, and always will be, 30 years away. But Hesslow says this is no reason to stop trying: “Fusion is a clean, safe and sustainable energy source, requiring very little fuel which is available from accessible reserves—a main component can be obtained from ordinary seawater.
“It offers a perfect complement to weather-dependent energy sources such as solar and wind. It also takes up very little space meaning more room for nature areas and farming—this is good considering the growing population on Earth.
Hesslow says she believes fusion energy will become a large energy source in the future, but economics will play a big role in determining when this is. Hesslow says she and the team now plan to use all the models they have built up over many years to finally solve the runaway electron problem.
“Many believe it will work, but it’s easier to travel to Mars than it is to achieve fusion,” she said. “You could say that we are trying to harvest stars here on Earth, and that can take time. It takes incredibly high temperatures, hotter than the center of the sun, for us to successfully achieve fusion here on Earth. That’s why I hope research is given the resources needed to solve the energy issue in time.”
Commenting on the study, David Kingham, CEO of Tokamak Energy, a U.K.-based fusion company, tells Newsweek : “This paper makes an important contribution to solving an awkward problem of serious damage to very large tokamaks.” However, he says that for smaller reactors such as the ones his company uses, “the proposed solution of injecting heavy ions will have the unwelcome consequence of cooling the plasma,” Kingham says. He suggests the research is likely to benefit to huge tokamaks, such as ITER, an international nuclear fusion research “megaproject” based in France.