An international team of scientists and engineers led by UCSD and General Atomics developed a technique to observe the flow of energy during the first phase of nuclear fusion reactions.
The team, whose findings were published in Nature Physics on Jan. 11, approached thermonuclear ignition through a process called fast ignition. Unlike traditional thermonuclear techniques that simultaneously use compression and ignition phases of fuel capsules, fast ignition separates the two different phases and implements a high-intensity ultrashort-pulse laser to provide the spark for ignition.
Mingsheng Wei, a researcher at General Atomics, told the UCSD Guardian that the team was not expecting to see a horseshoe pattern emission — which revealed that the energy did not flow directly — as the goal was to concentrate emission on the tip of the cone.
“Though we could clearly see the fluorescent emissions lighting up, we were surprised to see that it wasn’t lighting up in a forward direction,” Wei said. “When we sent in the short-pulse laser, we were hoping to see just the tip of the cone lighting up — but we didn’t see that. Instead, we saw a kind of hollow, horseshoe feature because energy was actually flowing out sideways.”
Farhat Beg, director of UCSD’s Center for Energy Research, said that the implications of the study include more efficient energy coupling.
“Before, people were working in the dark in regards to the flow of energy but here we’ve visualized and shown where the energy is going — it’s not where it’s supposed to go,” Beg told the Guardian. “With this understanding we can target the parameters and improve them to get more energy coupled to the fuel where fusion is going to happen.”
Wei said that after the first round of improvements the team was able to achieve the highest recorded energy deposition in the National Ignition Facility.
“It’s a lot of development and iterations, but after further improvements to the target and design by minimizing pre-plasma within the cone, we were able to get energy deposition closer to the cone tip,” Wei said. “From the calculations we inferred that up to 7 percent of the short-pulse laser energy were deposited into the fusion target — the highest kind of record for that facility.”
Christopher McGuffey, an assistant research scientist at the Center for Energy Research said that even though the goal is to eventually develop a sustainable energy source, they have yet to show that they can control nuclear fusion.
“Long term, the goal [for] many of us is to make a sustainable energy or power source, but many steps still remain,” McGuffey told the Guardian. “What we’ve done is see if we can make improvements and haven’t yet demonstrated that [controlled nuclear fusion is] feasible. There are still quite a few … challenges, like collecting all the energy that comes out in fusion reactions. I’d say there are still many decades before it will be used in a power plant that puts energy on the grid.”