In fall 2009, when Ethan Peterson ’13 arrived at MIT as an undergraduate, he already had some concepts about doable profession choices. He’d all the time favored constructing issues, at the same time as a toddler, so he imagined his future work would contain engineering of some type. He additionally favored physics. And he’d lately turn into intent on lowering our dependence on fossil fuels and concurrently curbing greenhouse fuel emissions, which made him think about finding out photo voltaic and wind vitality, amongst different renewable sources.
Issues crystallized for him within the spring semester of 2010, when he took an introductory course on nuclear fusion, taught by Anne White, throughout which he found that when a deuterium nucleus and a tritium nucleus mix to provide a helium nucleus, an brisk (14 mega electron volt) neutron — touring at one-sixth the velocity of sunshine — is launched. Furthermore, 1020 (100 billion billion) of those neutrons can be produced each second {that a} 500-megawatt fusion energy plant operates. “It was eye-opening for me to be taught simply how energy-dense the fusion course of is,” says Peterson, who grew to become the Class of 1956 Profession Growth Professor of nuclear science and engineering in July 2024. “I used to be struck by the richness and interdisciplinary nature of the fusion subject. This was an engineering self-discipline the place I might apply physics to resolve a real-world drawback in a means that was each attention-grabbing and exquisite.”
He quickly grew to become a physics and nuclear engineering double main, and by the point he graduated from MIT in 2013, the U.S. Division of Power (DoE) had already determined to chop funding for MIT’s Alcator C-Mod fusion undertaking. In view of that facility’s impending closure, Peterson opted to pursue graduate research on the College of Wisconsin. There, he acquired a fundamental science background in plasma physics, which is central not solely to nuclear fusion but additionally to astrophysical phenomena such because the photo voltaic wind.
When Peterson obtained his PhD from Wisconsin in 2019, nuclear fusion had rebounded at MIT with the launch, a 12 months earlier, of the SPARC undertaking — a collaborative effort being carried out with the newly based MIT spinout Commonwealth Fusion Methods. He returned to his alma mater as a postdoc after which a analysis scientist within the Plasma Science and Fusion Heart, taking his time, at first, to determine how you can finest make his mark within the subject.
Minding your neutrons
Round that point, Peterson was collaborating in a neighborhood planning course of, sponsored by the DoE, that targeted on essential gaps that wanted to be closed for a profitable fusion program. In the middle of these discussions, he got here to appreciate that insufficient consideration had been paid to the dealing with of neutrons, which carry 80 p.c of the vitality popping out of a fusion response — vitality that must be harnessed for electrical technology. Nonetheless, these neutrons are so energetic that they’ll penetrate by many tens of centimeters of fabric, doubtlessly undermining the structural integrity of parts and damaging very important gear comparable to superconducting magnets. Shielding can also be important for safeguarding people from dangerous radiation.
One objective, Peterson says, is to attenuate the variety of neutrons that escape and, in so doing, to scale back the quantity of misplaced vitality. A complementary goal, he provides, “is to get neutrons to deposit warmth the place you need them to and to cease them from depositing warmth the place you don’t need them to.” These concerns, in flip, can have a profound affect on fusion reactor design. This department of nuclear engineering, known as neutronics — which analyzes the place neutrons are created and the place they find yourself going — has turn into Peterson’s specialty.
It was by no means a high-profile space of analysis within the fusion neighborhood — as plasma physics, for instance, has all the time garnered extra of the highlight and extra of the funding. That’s precisely why Peterson has stepped up. “The impacts of neutrons on fusion reactor design haven’t been a excessive precedence for a very long time,” he says. “I felt that some initiative wanted to be taken,” and that prompted him to make the swap from plasma physics to neutronics. It has been his principal focus ever since — as a postdoc, a analysis scientist, and now as a school member.
A code to design by
One of the best ways to get a neutron to switch its vitality is to make it collide with a lightweight atom. Lithium, with an atomic variety of three, or lithium-containing supplies are usually good selections — and needed for producing tritium gas. The location of lithium “blankets,” that are meant to soak up vitality from neutrons and produce tritium, “is a essential a part of the design of fusion reactors,” Peterson says. Excessive-density supplies, comparable to lead and tungsten, can be utilized, conversely, to dam the passage of neutrons and different varieties of radiation. “You would possibly wish to layer these high- and low-density supplies in a sophisticated means that isn’t instantly intuitive” he provides. Figuring out which supplies to place the place — and of what thickness and mass — quantities to a difficult optimization drawback, which can have an effect on the dimensions, value, and effectivity of a fusion energy plant.
To that finish, Peterson has developed modelling instruments that may make analyses of those types simpler and quicker, thereby facilitating the design course of. “This has historically been the step that takes the longest time and causes the largest holdups,” he says. The fashions and algorithms that he and his colleagues are devising are basic sufficient, furthermore, to be appropriate with a various vary of fusion energy plant ideas, together with those who use magnets or lasers to restrict the plasma.
Now that he’s turn into a professor, Peterson is able to introduce extra individuals to nuclear engineering, and to neutronics particularly. “I like educating and mentoring college students, sharing the issues I’m enthusiastic about,” he says. “I used to be impressed by all of the professors I had in physics and nuclear engineering at MIT, and I hope to present again to the neighborhood in the identical means.”
He additionally believes that if you’re going to work on fusion, there isn’t any higher place to be than MIT, “the place the amenities are second-to-none. Individuals listed below are extraordinarily progressive and passionate. And the sheer quantity of people that excel of their fields is staggering.” Nice concepts can typically be sparked by off-the-cuff conversations within the hallway — one thing that occurs extra regularly than you anticipate, Peterson remarks. “All of this stuff taken collectively makes MIT a really particular place.”
