Nuclear fusion experiment reveals unexpected physics inside ‘burning plasma’

Scientists working on the dream of nuclear fusion, a form of energy that could potentially provide abundant clean energy in the future, have discovered surprising and unexplained behavior among particles in a government lab, a new study reports. The findings hint at the mysterious fundamental physics underlying nuclear fusion reactions, which power the Sun and other stars.

Researchers at the National Ignition Facility (NIF), a device of the US Department of Energy’s Lawrence Livermore National Laboratory (LLNL), recently celebrated the milestone to create what is known as a “burning plasma”, which is an energetic state of matter that is primarily maintained by “alpha particles” created by fusion reactions. NIF has also reached the threshold of producing “ignition”, i.e. fusion reactions that are self-sustaining, which is a major breakthrough, although it will likely still take decades to develop. a fusion reactor – assuming that’s possible.

Now, a team led by LLNL physicist Ed Hartouni has revealed that particles inside burning plasmas have surprisingly high energies that could open new windows into the exotic physics of fusion reactors, which “could be important for achieving robust and repeatable ignition,” according to a study published on Monday in Natural Physics.

“It’s a new plasma diet; NIF diagnostics have made it possible to study these things in ways that we couldn’t do before,” Hartouni said in a call with Motherboard that also included study authors Alastair Moore, a physicist at LLNL, and Aidan Crilly, associate researcher in plasma physics. at Imperial College London. “We’re able to see things at a level we haven’t been able to see before, and there are surprises with these plasmas in a real lab.”

“It’s a really exciting time for us to finally have a quasi-ignition facility and experiments to understand this physics that we haven’t really been able to understand before and start to get to the point where we can think what a future fusion facility might look like,” Moore added.

The team discovered the strange behavior of the ions by examining observations from several experiments that took place at NIF in recent years. These tests involve the fusion between particles called ions, which are atoms that do not have the same number of positive and negative components (protons and electrons), leaving them with an electrical charge.

By using dozens of lasers to heat deuterium and tritium ions, which are both heavier versions of hydrogen, NIF researchers generate fusion reactions between the ions. In a burning plasma, reactions between ions produce new entities, called alpha particles, which raise higher temperatures which, in turn, trigger even more reactions in a thermonuclear burn.

Hartouni and colleagues have now shown that NIF experiments that produce alpha particles consistently show ions with higher energies than those predicted by the models, although the source of these energy increases “is an open experimental question”, according to the study. The team presented four possible explanations for the sighting, including so-called “kinetic effects” that have been speculated in previous theories, but more experiments and meticulous research will be needed to understand the underlying mechanisms. at work in the plasma.

“It’s a mystery, but there are several hypotheses,” Crilly said. “Whether it’s a single effect, like this kinetic effect, or a combination of them and they all add their little bit to that gap.”

“It’s worth thinking about just how extreme these conditions are and why it’s difficult,” he added, noting that NIF fusion reactions occur at temperatures around 180 million degrees Fahrenheit. and under conditions 30 times denser than the Sun. In this otherworldly environment “we need to understand exactly how an alpha particle collides with all these other particles and distributes its energy and how they all collide,” Crilly noted.

To that end, the team plans to continue looking for clues to the strange behavior of ions in models and experiments. Since the NIF has produced this unprecedented insight into the weird world of fusion reactions, the facility is bound to come up with weird new ideas no matter what direction their research takes them.

“We’ve never been able to study this before,” Moore said. “It’s the first burning plasma we’ve ever created on the planet, so it’s pretty amazing.”