Big fusion milestones are rare things. But a team based at the National Ignition Facility (NIF) says they’ve reached one. For the first time, they’ve been able to get their deuterium-tritium fuel to fuse so that it produces more energy than was deposited into it.
The researchers are quick to note they’ve not achieved the long-awaited goal of ignition—a self-sustaining fusion reaction that produces more energy than what is sent into the experiment. Most of the 1.8 megajoules of energy in the facility’s lasers is still lost in the effort to achieve the temperatures and pressures needed to get fusion started. This process involves hitting the inside of a cylindrical gold container with 192 lasers in order to produce X-rays. That radiation then heats and blasts away the outer layer of a spherical capsule suspended at the center of the cylinder. The reaction force sends the remainder of this target inwards, compressing some 170 micrograms of frozen deuterium-tritium fuel at the center.
Today only about 1 percent of the energy poured into the cylinder actually winds up in the fuel. Still, team leader Omar Hurricane told reporters in a press briefing on Monday that this latest milestone is “kind of a major turning point in a lot of our minds.” The results are published this week in a paper in Nature. (A similar announcement was made in August of last year, when some 8000 joules of energy were released in the form of neutrons. In this paper, the team reports yields as high as 17 000 joules.)
The team is also encouraged by evidence of what’s called alpha particle heating—a process by which helium atoms created in fusion reactions deposit their energy into the fuel instead of escaping. This “bootstrapping” process—using fusion to create more fusion—is what will be needed to ultimately get the yield up to ignition levels. Via National Ignition Facility Achieves Record Energies