In the world of renewable energy, there is perhaps no more ambitious goal than fusion energy. It involves the fusion of hydrogen atoms to create helium, a process that generates an unholy amount of energy. It’s a reaction that happens every moment in the sun, but reproducing it on Earth is a much more rare and arduous process. If we are successful, however, we would have access to a clean source of renewable electricity that meets our ever-increasing energy needs.
To that end, the researchers are pursuing a phenomenon called “ignition,” which occurs when a fusion reactor generates more energy than was needed to create the initial reaction. A few major attempts are underway to achieve this goal, including the International Thermonuclear Experimental Reactor (ITER) in France. This effort uses powerful magnets in a machine called a tokamak to create superheated plasma created using hydrogen.
But therein lies a problem: there’s only so much hydrogen you can put in a tokamak before it all starts to go wrong.
“One of the limitations of making plasma inside a tokamak is the amount of hydrogen you can inject into it,” Paolo Ricci, a researcher at the Swiss Plasma Center, said in a press release. “Since the early days of fusion, we’ve known that if you try to increase the density of the fuel, at some point there’s going to be what we call a ‘disruption’ – basically you totally lose containment, and plasma goes everywhere.”
To solve this problem, scientists started researching different equations to measure the maximum amount of hydrogen you can put inside a tokamak before disruption. A law that eventually took hold and became a mainstay in the world of fusion research is known as the “Greenwald limit”, which states that the amount of fuel that can be used in a tokamak is directly correlated in the radius of the machine. The researchers behind ITER even built their machine based on this law.
But even Greenwald’s limit was not perfect.
“The Greenwald limit is what we call an ’empirical’ limit or law, which basically means it’s like an empirical rule based on observations made in past experiments,” said experimental physicist Alex Zylstra. at the Lawrence Livermore National Laboratory in California. , told the Daily Beast in an email. “These are very useful, but we must always be careful when applying them outside of the conditions where we have data from experiments.”
That’s why Ricci and his team challenged that long-held belief in a new article published May 6 in the journal Physical examination letters. In it, they postulate that the Greenwald limit can actually be increased by almost double, or almost double the amount of hydrogen that can enter a tokamak in order to produce plasma. Their findings could lay the groundwork for future fusion reactors such as DEMO, an ITER successor under development, to finally achieve ignition.
“It’s important because it shows that the density you can achieve in a tokamak increases with the power you need to run it,” Ricci said. “In fact, DEMO will operate at much higher power than current tokamaks and ITER, which means you can add more fuel density without limiting production, contrary to Greenwald’s law. And that’s a very good news. “
Zylstra thinks the team’s discovery is important because it sheds light on why exactly fusion reactors also have such a limit. It also shows that tokamak designs like ITER or DEMO could be “less constrained than previously thought”. With fuel density being doubled, this could lead to a big improvement in their power output by tokamaks – and ultimately lead us to ignition.
“Fusion is an extremely difficult problem, both scientifically and technologically, and making fusion power a reality requires many advances, one step at a time,” Zylstra added. “If this study is further validated, especially on machines like ITER, it will certainly help the magnetic fusion community to credibly design and optimize future experimental and power generation facility designs.”