What would it take to refuel the sun?
It’s a question that fusion scientists have mulled over for decades – and now a team of researchers at the College of William and Mary, in partnership with the U.S. Department of Energy, are closer than ever to finding out.
The DOE recently announced $36.4 million in funding for 37 research awards at universities, laboratories and private firms to support the study of nuclear fusion as a future energy source, with William and Mary on the list of universities selected.
Saskia Mordijck, assistant professor of applied science at the college, laid the groundwork for the DOE partnership and regularly collaborates with scientists at the DIII-D National Fusion Facility at General Atomics in San Diego. She says William & Mary will receive about $1 million of the $36.4 million package, which will go towards hiring a fusion scientist and two graduate student researchers.
Their plan? Learn how to fuel the plasma needed for fusion reactions, like those that power the sun.
“If you think about the sun, it is a nuclear reactor and, in about 5 billion years, it will stop because it has run out of fuel,” Mordijck said. “It will die out as a star, because the hydrogen needed for fusion reactions is depleted. We’re trying to figure out a way to fuel the plasma to keep those reactions going in an Earth-based fusion reactor.”
Within the sun, the fusion of hydrogen nuclei into helium has produced enough energy to warm Earth for billions of years. The temperatures needed for fusion result in a state of matter known as plasma.
The mechanics of how that plasma is created is relatively simple to explain, but extremely complicated to produce, according to Mordijck.
To accomplish fusion, two small particles are heated to a high enough temperature that they fuse together. In fusing, some of their mass is released and converted into energy.
If done correctly, the resulting energy will be greater than the energy required to fuse the two particles together. It’s essentially the opposite of fission, the method of breaking apart atoms that fuels nuclear power plants and atomic bombs.
“With fission, you can just shoot a fast neutron at a large particle and then it splits and releases energy,” Mordijck said. “The problem with fusion is you need to bring two particles together. That is very difficult, because they repel each other.”
When it works, a fusion reaction produces much more energy than fission, she explained. The problem is getting the particles to get along.
“I compare it to college, in the sense that college is the time when people tend to make the most friends,” she said. “Why? You pick the college that fits your personality and all the other people there did the same thing. The other students already have a similar resonance with you.”
Mordijck says that, like college, the trick to achieving fusion is creating a climate that fosters bonding.
“In college, you put enough students together and you keep them there for four years, so they can actually make and build friendships,” she said. “With fusion, it’s similar. You are forcing relationships, so you need to get the temperatures high enough, with enough particles and you need to keep them together long enough so they fuse.”
Mordijck’s research focuses on containing plasma by using magnetic fields, unlike solar plasma, which is contained by the sun’s massive gravity. Her fusion-control experiments are conducted on an instrument known as a tokamak, a donut-shaped chamber designed to accommodate the magnetic fields needed to contain the plasma. Her ultimate goal — and the goal of every fusion researcher — is to achieve a contained, self-sustaining fusion reaction.
The next phase of Mordjick’s research will focus on what the DOE calls a “high-priority challenge,” creating a hot and dense enough plasma to keep a fusion reaction going by somehow adding more fuel. To employ Mordjick’s college metaphor, her team will have to figure out how to enroll more students without upsetting any existing bonds.
“This is an incredibly complex thing to do,” Mordijck said. “You are trying to create a sun on Earth — and not only are you trying to create it, you want to keep it that way for hours and get energy from it. It’s extremely hard, but it’s like anything challenging, it takes effort and it takes time.”