Fusion energy needs more than a sustained fusion reaction before it can help the world produce sufficient carbon-neutral energy. The U.S. Department of Energy has identified a research and development agenda for a suite of technologies and processes to enable fusion.
Two DOE officials named five of those pressing technologies in a webinar Thursday hosted by the National Academies of Science, Engineering and Medicine (NASEM). More are covered in a 2021 NASEM report that urges rapid development of fusion-enabling tech:
“Although this is often put off for the future, the goal of economical fusion energy within the next several decades as a U.S. strategic interest drives the need to rapidly increase the research and development of enabling materials, components, and fusion nuclear technologies.”
The five highlighted Thursday include:
1 Fusion-Proof Materials
The plasma in which the fusion reaction occurs can be hotter than the sun. A powerful magnetic field or inertia can confine the plasma, buffering it from reactor walls and components, but fusion reactors nonetheless will require materials that can handle extreme heat and bombardment by neutrons set loose when hydrogen isotopes transform into helium.
To test potential materials, scientists need to produce conditions similar to a fusion reaction.
“There is a very dire need for a fusion-prototypic neutron source to be able to gather the materials data, which can take many years of exposure,” said Scott Hsu, DOE’s lead fusion coordinator. While that neutron source is in development, he added, machine learning and materials testing can help narrow the number of candidate materials.
There is also the potential to avoid materials entirely by using “truly transformative first wall and blanket designs, where you may not even have any solid material facing the plasma, and that almost sidesteps the issue of materials,” Hsu said. “And we do need to keep those ideas on the table.”
2 A Tritium Breeder
The most common fusion-reactor designs use two isotopes of hydrogen—deuterium (2H) and Tritium (3H)—as fuel.
“If we’re going to use a deuterium-tritium fuel cycle, we’re going to have to extract the heat and breed tritium,” said Richard Hawryluk, senior technical advisor at the DOE Office of Science and chair of the 2021 NASEM report.
“A particular challenge is the need to safely and efficiently close the fuel cycle,” that report states, “which for deuterium-tritium fusion designs involves the development of blankets to breed and extract tritium, as well as the fueling, exhausting, confining, extracting, and separating tritium in significant quantities.”
3 An Exhaust System
Some of the unfathomable heat produced in a fusion reaction will be used to produce power, but first it has to be managed. The reactor also has to capture exhaust, including the helium, from the plasma.
“A full research program will require test facilities producing environments increasingly similar to a fusion power plant to assess reactor-relevant power exhaust handling in the fusion neutron environment,” the NASEM report states.
4 More Efficient Lasers
DOE’s National Ignition Facility (NIF) celebrated a long-sought accomplishment in December when it sparked a fusion reaction that released more energy (3.15 megajoules) than the beams from the laser that ignited it (2.05 megajoules). But it took 300 megajoules to power the laser.
Eventually, such lasers will be powered, after their startup, by electricity from the fusion reactor. But more efficient lasers mean more efficient reactors, leaving more power for the user or the grid.
It’s not enough for the laser to be efficient. It also has to operate less like a musket and more like a machine gun.
“The wonderful result at NIF,” Hawryluk said, “we got to that point by doing a few shots per year. You have to be able to get to the point where you’re doing a few shots per second, or a shot per second, so it’s the repetition rate, as well, that we have to master.”
That increases the repetition rate for every step in the process, starting with the fuel capsule. According to the journal Science, “One million capsules a day would need to be made, filled, positioned, blasted, and cleared away—a huge engineering challenge.”