It’s no secret that there is a modern-day gold rush going on in AI development. According to the 2024 Work Trend Index by Microsoft and Linkedin, over 40% of business leaders anticipate completely redesigning their business processes from the ground up using artificial intelligence (AI) within…
Killing the messenger
Like humans and other complex multicellular organisms, single-celled bacteria can fall ill and fight off viral infections. A bacterial virus is caused by a bacteriophage, or, more simply, phage, which is one of the most ubiquitous life forms on earth. Phages and bacteria are engaged in a constant battle, the virus attempting to circumvent the bacteria’s defenses, and the bacteria racing to find new ways to protect itself.
These anti-phage defense systems are carefully controlled, and prudently managed — dormant, but always poised to strike.
New open-access research recently published in Nature from the Laub Lab in the Department of Biology at MIT has characterized an anti-phage defense system in bacteria, CmdTAC. CmdTAC prevents viral infection by altering the single-stranded genetic code used to produce proteins, messenger RNA.
This defense system detects phage infection at a stage when the viral phage has already commandeered the host’s machinery for its own purposes. In the face of annihilation, the ill-fated bacterium activates a defense system that will halt translation, preventing the creation of new proteins and aborting the infection — but dooming itself in the process.
“When bacteria are in a group, they’re kind of like a multicellular organism that is not connected to one another. It’s an evolutionarily beneficial strategy for one cell to kill itself to save another identical cell,” says Christopher Vassallo, a postdoc and co-author of the study. “You could say it’s like self-sacrifice: One cell dies to protect the other cells.”
The enzyme responsible for altering the mRNA is called an ADP-ribosyltransferase. Researchers have characterized hundreds of these enzymes — although a few are known to target DNA or RNA, all but a handful target proteins. This is the first time these enzymes have been characterized targeting mRNA within cells.
Expanding understanding of anti-phage defense
Co-first author and graduate student Christopher Doering notes that it is only within the last decade or so that researchers have begun to appreciate the breadth of diversity and complexity of anti-phage defense systems. For example, CRISPR gene editing, a technique used in everything from medicine to agriculture, is rooted in research on the bacterial CRISPR-Cas9 anti-phage defense system.
CmdTAC is a subset of a widespread anti-phage defense mechanism called a toxin-antitoxin system. A TA system is just that: a toxin capable of killing or altering the cell’s processes rendered inert by an associated antitoxin.
Although these TA systems can be identified — if the toxin is expressed by itself, it kills or inhibits the growth of the cell; if the toxin and antitoxin are expressed together, the toxin is neutralized — characterizing the cascade of circumstances that activates these systems requires extensive effort. In recent years, however, many TA systems have been shown to serve as anti-phage defense.
Two general questions need to be answered to understand a viral defense system: How do bacteria detect an infection, and how do they respond?
Detecting infection
CmdTAC is a TA system with an additional element, and the three components generally exist in a stable complex: the toxic CmdT, the antitoxin CmdA, and an additional component called a chaperone, CmdC.
If the phage’s protective capsid protein is present, CmdC disassociates from CmdT and CmdA and interacts with the phage capsid protein instead. In the model outlined in the paper, the chaperone CmdC is, therefore, the sensor of the system, responsible for recognizing when an infection is occurring. Structural proteins, such as the capsid that protects the phage genome, are a common trigger because they’re abundant and essential to the phage.
The uncoupling of CmdC exposes the neutralizing antitoxin CmdA to be degraded, which releases the toxin CmdT to do its lethal work.
Toxicity on the loose
The researchers were guided by computational tools, so they knew that CmdT was likely an ADP-ribosyltransferase due to its similarities to other such enzymes. As the name suggests, the enzyme transfers an ADP ribose onto its target.
To determine if CmdT interacted with any sequences or positions in particular, they tested a mix of short sequences of single-stranded RNA. RNA has four bases: A, U, G, and C, and the evidence points to the enzyme recognizing GA sequences.
The CmdT modification of GA sequences in mRNA blocks their translation. The cessation of creating new proteins aborts the infection, preventing the phage from spreading beyond the host to infect other bacteria.
“Not only is it a new type of bacterial immune system, but the enzyme involved does something that’s never been seen before: the ADP-ribsolyation of mRNA,” Vassallo says.
Although the paper outlines the broad strokes of the anti-phage defense system, it’s unclear how CmdC interacts with the capsid protein, and how the chemical modification of GA sequences prevents translation.
Beyond bacteria
More broadly, exploring anti-phage defense aligns with the Laub Lab’s overall goal of understanding how bacteria function and evolve, but these results may have broader implications beyond bacteria.
Senior author Michael Laub, Salvador E. Luria Professor and Howard Hughes Medical Institute Investigator, says the ADP-ribosyltransferase has homologs in eukaryotes, including human cells. They are not well studied, and not among the Laub Lab’s research topics, but they are known to be up-regulated in response to viral infection.
“There are so many different — and cool — mechanisms by which organisms defend themselves against viral infection,” Laub says. “The notion that there may be some commonality between how bacteria defend themselves and how humans defend themselves is a tantalizing possibility.”
How examining conflict can be “intellectually serious” and “incredibly fun”
The banging on the tables begins almost immediately.
It’s September, and the 53 first-year students in MIT’s Concourse program are debating the pros and cons of capitalism during one of their Friday lunchtime seminars in Building 16. Sasha Rickard ’19 — assistant director of Concourse and the chair, or moderator, of the debate — reminds everyone of the rules: “Stand when you speak, address your questions and comments to the chair, and if you hear someone saying something you support, give them a little bang on the table.” The first speaker walks to the podium, praises the benefits of capitalism for her allotted four minutes, and is rewarded with a cacophony of table-banging.
Other students jump up to question her argument. The next speaker takes the opposite view, denouncing capitalism. For nearly two hours, there are more speeches on both sides of the issue, more questions, more enthusiastic banging on tables. Participants call the back-and-forth “intellectually serious,” “genuine good-faith engagement,” and “incredibly fun.”
The debate is one of the cornerstones of MIT’s Civil Discourse Project, a joint venture between the Concourse program and philosophy professors Brad Skow and Alex Byrne. The premise behind the Civil Discourse Project is that first-year students who practice talking and listening to each other even when they disagree will become more thoughtful and open-minded citizens, during their time at MIT and beyond.
“It’s consistent with free expression and free speech, but also consistent with the mission of the university, which is teaching and learning and getting to a greater sense of the truth,” says Linda Rabieh, a senior lecturer in the Concourse program and co-leader of the Civil Discourse Project with Skow, Byrne, and Concourse Director Anne McCants.
The project appears to be working. First-year Ace Chun, one of the student debaters, says,“It’s easy to just say, ‘Well, you have your opinion and I have mine,’ or ‘You’re wrong and I’m right.’ But going through the process of disagreement and coming up with a more informed position feels really important.”
It’s debatable
Funded by the Arthur Vining Davis Foundations, the project launched in fall 2023 as a series of paired events. First, two scholars with opposing views on a particular subject — often one from MIT and one from another institution — participate in a formal debate on campus. A week or two later, the Concourse students, having seen the first debate, hold their own version on the same topic. Past debates have explored feminism, climate change, Covid-19 public-health policies, and the Israel-Hamas conflict in Gaza.
This year’s first scholar debate explored the question “Is capitalism defensible?” and featured economist Tyler Cowen of George Mason University, who argued in the affirmative, and political scientist Alex Gourevitch of Brown University, who vigorously disagreed. Roughly 350 people registered to watch the two take turns delivering prepared remarks and answering audience questions in a large auditorium in the Stata Center.
These debates are open to everyone at MIT, as well as the public. They are not recorded or livestreamed because, Skow says, “we want people to feel free to say whatever’s on their mind without worrying that it’s going to be on the internet forever.” Concourse students in attendance look for ideas for what they might say in their own debate, but also, Rabieh says, how they might say it. Cowen and Gourevitch remained respectful even when their exchanges grew louder and hotter, and they ended the evening with a handshake. Students “were seeing reasonable people disagree,” Rabieh says.
Five or six years ago, Rabieh had begun to notice a reluctance among students to talk about controversial ideas; they didn’t want to risk offending anyone. “Most MIT students spend a lot of their time doing math, science, or engineering, and it’s tempting for them to take refuge in the certainty of quantitative reasoning,” she says.
Today’s combative political and cultural landscape can make it even harder to get students talking about hot-button issues, and as a result, civil discourse has become something of a holy grail in higher education. Some institutions (including MIT) now incorporate free-speech exercises into their orientation programs; others host “conversation” events or offer special faculty training. Byrne sees MIT’s Civil Discourse Project, with its connection to the Concourse curriculum, as consistent, pragmatic, hands-on learning. “We’re talking instead of just talking about talking,” he says. “It’s like swimming. It’s all very well to hear a lecture about pool etiquette — stay in your lane, don’t dive-bomb your fellow swimmers — but at some point, you have to actually get in the pool.”
Learning to argue
Concourse’s “pool” can be found in a student lounge in Building 16. That’s where a group of “debate fellows” — older students who have gone through the Concourse program themselves — coach the first-year students in crafting statements and speeches that can be presented at a debate. It’s also where the fellows help Rabieh and Rickard adapt the original debate question into a resolution the younger students can reasonably argue about. “Our students are still figuring out what they think about a lot of things,” Rickard says. So, the question debated by Cowen and Gourevitch — Is capitalism defensible? — becomes: “Capitalism is the best economic system because it prioritizes freedom and material wealth.”
The first-year students jumped in. During their lunchtime debate, they crowded around tables, ate lasagna and salad, and waited their turn at the podium. They told personal stories to illustrate their points. They tried arguing in support of an idea that they actually disagreed with. They admitted when they were stumped. “That’s a tricky question,” one of the speakers conceded.
“At a place like MIT, it’s easy to get caught up in your own world, like ‘I have this big assignment or I have this paper due,’” says debate fellow and senior Isaac Lock. “With the Civil Discourse Project, students are thinking about big ideas, maybe not having super-strong, solid opinions, but they’re at least considering them in ways that they probably haven’t done before.”
They’re also learning what a balanced conversation feels like. The student debates use a format developed by Braver Angels, a national organization that holds workshops and debates to try to bridge the partisan divide that exists in the United States today. With strict time limits and room for both prepared speeches and spontaneous remarks, the format “allows different types of people to speak,” says debate fellow Arianna Doss, a sophomore. “Because of the debates, we’re better-equipped to articulate our points and provide nuance — why I believe what I believe — while also acknowledging and understanding the shortcomings of our arguments.”
The Civil Discourse Project will publish more about its spring semester lectures on its website. Coleman Hughes, author of “The End of Race Politics: Arguments for a Colorblind America,” will be on campus March 3, and a debate on the relevance of legacy media is being planned for later in the semester.
Communications user terminal developed by MIT Lincoln Laboratory prepares for historic moon flyby
In 1969, Apollo 11 astronaut Neil Armstrong stepped onto the moon’s surface — a momentous engineering and science feat marked by his iconic words, “That’s one small step for a man, one giant leap for mankind.” Three years later, Apollo 17 became NASA’s final Apollo mission to land humans on the brightest and largest object in our night sky. Since then, no humans have visited the moon or traveled past low Earth orbit (LEO), largely because of shifting politics, funding, and priorities.
But that is about to change. Through NASA’s Artemis II mission, scheduled to launch no earlier than September 2025, four astronauts will be the first humans to travel to the moon in more than 50 years. In 2022, the uncrewed Artemis I mission proved the ability of NASA’s new spacecraft Orion — launched on the new heavy-lift rocket, the Space Launch System — to travel farther into space than ever before and return safely to Earth. Building on that success, the 10-day Artemis II mission will pave the way for Artemis III, which aims to land astronauts on the lunar surface, with the goal of establishing a future lasting human presence on the moon and preparing for human missions to Mars.
One big step for lasercom
Artemis II will be historic not only for renewing human exploration beyond Earth, but also for being the first crewed lunar flight to demonstrate laser communication (lasercom) technologies, which are poised to revolutionize how spacecraft communicate. Researchers at MIT Lincoln Laboratory have been developing such technologies for more than two decades, and NASA has been infusing them into its missions to meet the growing demands of long-distance and data-intensive space exploration.
As spacecraft push farther into deep space and advanced science instruments collect ultrahigh-definition (HD) data like 4K video and images, missions need better ways to transmit data back to Earth. Communication systems that encode data onto infrared laser light instead of radio waves can send more information at once and be packaged more compactly while operating with less power. Greater volumes of data fuel additional discoveries, and size and power efficiency translate to increased space for science instruments or crew, less expensive launches, and longer-lasting spacecraft batteries.
For Artemis II, the Orion Artemis II Optical Communications System (O2O) will send high-resolution video and images of the lunar surface down to Earth — a stark contrast to the blurry, grainy footage from the Apollo program. In addition, O2O will send and receive procedures, data files, flight plans, voice calls, and other communications, serving as a high-speed data pipeline between the astronauts on Orion and mission control on Earth. O2O will beam information via lasers at up to 260 megabits per second (Mbps) to ground optical stations in one of two NASA locations: the White Sands Test Facility in Las Cruces, New Mexico, or the Jet Propulsion Laboratory’s Table Mountain Facility in Wrightwood, California. Both locations are ideal for their minimal cloud coverage, which can obstruct laser signals as they enter Earth’s atmosphere.
At the heart of O2O is the Lincoln Laboratory–developed Modular, Agile, Scalable Optical Terminal (MAScOT). About the size of a house cat, MAScOT features a 4-inch telescope mounted on a two-axis pivoted support (gimbal), and fixed back-end optics. The gimbal precisely points the telescope and tracks the laser beam through which communications signals are emitted and received, in the direction of the desired data recipient or sender. Underneath the gimbal, in a separate assembly, are the back-end optics, which contain light-focusing lenses, tracking sensors, fast-steering mirrors, and other components to finely point the laser beam.
A series of firsts
MAScOT made its debut in space as part of the laboratory’s Integrated Laser Communications Relay Demonstration (LCRD) LEO User Modem and Amplifier Terminal (ILLUMA-T), which launched to the International Space Station (ISS) in November 2023. After a few weeks of preliminary testing, ILLUMA-T transmitted its first beam of laser light to NASA’s LCRD satellite in geosynchronous (GEO) orbit 22,000 miles above Earth’s surface. Achieving this critical step, known as “first light,” required precise pointing, acquisition, and tracking of laser beams between moving spacecraft.
Over the following six months, the laboratory team performed experiments to test and characterize the system’s basic functionality, performance, and utility for human crews and user applications. Initially, the team checked whether the ILLUMA-T-to-LCRD optical link was operating at the intended data rates in both directions: 622 Mbps down and 51 Mbps up. In fact, even higher data rates were achieved: 1.2 gigabits per second down and 155 Mbps up.
“This first demonstration of a two-way, end-to-end laser communications relay system, in which ILLUMA-T was the first LEO user of LCRD, is a major milestone for NASA and other space organizations,” says Bryan Robinson, leader of the laboratory’s Optical and Quantum Communications Group. “It serves as a precursor to optical relays at the moon and Mars.”
After the relay was up and running, the team assessed how parameters such as laser transmit power, optical wavelength, and relative sun angles impact terminal performance. Lastly, they contributed to several networking experiments over multiple nodes to and from the ISS, using NASA’s delay/disruption tolerant networking protocols. One landmark experiment streamed 4K video on a round-trip journey from an airplane flying over Lake Erie in Ohio, to the NASA Glenn Research Center in nearby Cleveland, to the NASA White Sands Test Facility in New Mexico, to LCRD in GEO, to ILLUMA-T on the ISS, and then back. In June 2024, ILLUMA-T communicated with LCRD for the last time and powered off.
“Our success with ILLUMA-T lays the foundation for streaming HD video to and from the moon,” says co-principal investigator Jade Wang, an assistant leader of the Optical and Quantum Communications Group. “You can imagine the Artemis astronauts using videoconferencing to connect with physicians, coordinate mission activities, and livestream their lunar trips.”
Moon ready
The Artemis II O2O mission will employ the same overall MAScOT design proven on ILLUMA-T. Lincoln Laboratory delivered the payload to NASA’s Kennedy Space Center for installation and testing on the Orion spacecraft in July 2023.
“Technology transfer to government is what Lincoln Laboratory does as a federally funded research and development center,” explains lead systems engineer Farzana Khatri, a senior staff member in the Optical and Quantum Communications Group. “We not only transfer technology, but also work with our transfer partner to ensure success. To prepare for O2O, we are leveraging lessons learned during ILLUMA-T operations. Recently, we conducted pre-mission dry runs to enhance coordination among the various teams involved.”
In August 2024, the laboratory completed an important milestone for the O2O optical terminal: the mission readiness test. The test involved three phases. In the first phase, they validated terminal command and telemetry functions. While laboratory-developed ground software was directly used to command and control ILLUMA-T, for O2O, it will run in the background and all commands and telemetry will be interfaced through software developed by NASA’s Johnson Space Center Mission Control Center. In the second phase, the team tested different user applications, including activating some of Orion’s HD cameras and sending videos from Cape Canaveral to Johnson Space Center as a mock-up for the actual space link. They also ran file transfers, video conferencing, and other operations on astronaut personal computing devices. In the third phase, they simulated payload commissioning activities, such as popping the latch on the optical hardware and moving the gimbal, and conducting ground terminal operations.
“For O2O, we want to show that this optical link works and is helpful to astronauts and the mission,” Khatri says. “The Orion spacecraft collects a huge amount of data within the first day of a mission, and typically these data sit on the spacecraft until it lands and take months to be offloaded. With an optical link running at the highest rate, we should be able to get data down to Earth within a few hours for immediate analysis. Furthermore, astronauts can stay in touch with Earth during their journey, inspiring the public and the next generation of deep-space explorers, much like the Apollo 11 astronauts who first landed on the moon 55 years ago.”
O2O is funded by the Space Communication and Navigation program at NASA Headquarters in Washington. O2O was developed by a team of engineers from NASA’s Goddard Space Flight Center and Lincoln Laboratory. This collaboration has led to multiple lasercom missions, such as the 2013 Lunar Laser Communication Demonstration, the 2021 LCRD, the 2022 TeraByte Infrared Delivery, and the 2023 ILLUMA-T.
How conflict can be “intellectually serious” and “incredibly fun”
The banging on the tables begins almost immediately.
It’s September, and the 53 first-year students in MIT’s Concourse program are debating the pros and cons of capitalism during one of their Friday lunchtime seminars in Building 16. Sasha Rickard ’19 — assistant director of Concourse and the chair, or moderator, of the debate — reminds everyone of the rules: “Stand when you speak, address your questions and comments to the chair, and if you hear someone saying something you support, give them a little bang on the table.” The first speaker walks to the podium, praises the benefits of capitalism for her allotted four minutes, and is rewarded with a cacophony of table-banging.
Other students jump up to question her argument. The next speaker takes the opposite view, denouncing capitalism. For nearly two hours, there are more speeches on both sides of the issue, more questions, more enthusiastic banging on tables. Participants call the back-and-forth “intellectually serious,” “genuine good-faith engagement,” and “incredibly fun.”
The debate is one of the cornerstones of MIT’s Civil Discourse Project, a joint venture between the Concourse program and philosophy professors Brad Skow and Alex Byrne. The premise behind the Civil Discourse Project is that first-year students who practice talking and listening to each other even when they disagree will become more thoughtful and open-minded citizens, during their time at MIT and beyond.
“It’s consistent with free expression and free speech, but also consistent with the mission of the university, which is teaching and learning and getting to a greater sense of the truth,” says Linda Rabieh, a senior lecturer in the Concourse program and co-leader of the Civil Discourse Project with Skow, Byrne, and Concourse Director Anne McCants.
The project appears to be working. First-year Ace Chun, one of the student debaters, says,“It’s easy to just say, ‘Well, you have your opinion and I have mine,’ or ‘You’re wrong and I’m right.’ But going through the process of disagreement and coming up with a more informed position feels really important.”
It’s debatable
Funded by the Arthur Vining Davis Foundations, the project launched in fall 2023 as a series of paired events. First, two scholars with opposing views on a particular subject — often one from MIT and one from another institution — participate in a formal debate on campus. A week or two later, the Concourse students, having seen the first debate, hold their own version on the same topic. Past debates have explored feminism, climate change, Covid-19 public-health policies, and the Israel-Hamas conflict in Gaza.
This year’s first scholar debate explored the question “Is capitalism defensible?” and featured economist Tyler Cowen of George Mason University, who argued in the affirmative, and political scientist Alex Gourevitch of Brown University, who vigorously disagreed. Roughly 350 people registered to watch the two take turns delivering prepared remarks and answering audience questions in a large auditorium in the Stata Center.
These debates are open to everyone at MIT, as well as the public. They are not recorded or livestreamed because, Skow says, “we want people to feel free to say whatever’s on their mind without worrying that it’s going to be on the internet forever.” Concourse students in attendance look for ideas for what they might say in their own debate, but also, Rabieh says, how they might say it. Cowen and Gourevitch remained respectful even when their exchanges grew louder and hotter, and they ended the evening with a handshake. Students “were seeing reasonable people disagree,” Rabieh says.
Five or six years ago, Rabieh had begun to notice a reluctance among students to talk about controversial ideas; they didn’t want to risk offending anyone. “Most MIT students spend a lot of their time doing math, science, or engineering, and it’s tempting for them to take refuge in the certainty of quantitative reasoning,” she says.
Today’s combative political and cultural landscape can make it even harder to get students talking about hot-button issues, and as a result, civil discourse has become something of a holy grail in higher education. Some institutions (including MIT) now incorporate free-speech exercises into their orientation programs; others host “conversation” events or offer special faculty training. Byrne sees MIT’s Civil Discourse Project, with its connection to the Concourse curriculum, as consistent, pragmatic, hands-on learning. “We’re talking instead of just talking about talking,” he says. “It’s like swimming. It’s all very well to hear a lecture about pool etiquette — stay in your lane, don’t dive-bomb your fellow swimmers — but at some point, you have to actually get in the pool.”
Learning to argue
Concourse’s “pool” can be found in a student lounge in Building 16. That’s where a group of “debate fellows” — older students who have gone through the Concourse program themselves — coach the first-year students in crafting statements and speeches that can be presented at a debate. It’s also where the fellows help Rabieh and Rickard adapt the original debate question into a resolution the younger students can reasonably argue about. “Our students are still figuring out what they think about a lot of things,” Rickard says. So, the question debated by Cowen and Gourevitch — Is capitalism defensible? — becomes: “Capitalism is the best economic system because it prioritizes freedom and material wealth.”
The first-year students jumped in. During their lunchtime debate, they crowded around tables, ate lasagna and salad, and waited their turn at the podium. They told personal stories to illustrate their points. They tried arguing in support of an idea that they actually disagreed with. They admitted when they were stumped. “That’s a tricky question,” one of the speakers conceded.
“At a place like MIT, it’s easy to get caught up in your own world, like ‘I have this big assignment or I have this paper due,’” says debate fellow and senior Isaac Lock. “With the Civil Discourse Project, students are thinking about big ideas, maybe not having super-strong, solid opinions, but they’re at least considering them in ways that they probably haven’t done before.”
They’re also learning what a balanced conversation feels like. The student debates use a format developed by Braver Angels, a national organization that holds workshops and debates to try to bridge the partisan divide that exists in the United States today. With strict time limits and room for both prepared speeches and spontaneous remarks, the format “allows different types of people to speak,” says debate fellow Arianna Doss, a sophomore. “Because of the debates, we’re better-equipped to articulate our points and provide nuance — why I believe what I believe — while also acknowledging and understanding the shortcomings of our arguments.”
The Civil Discourse Project will publish more about its spring semester lectures on its website. Coleman Hughes, author of “The End of Race Politics: Arguments for a Colorblind America,” will be on campus March 3, and a debate on the relevance of legacy media is being planned for later in the semester.
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Smart handling of neutrons is crucial to fusion power success
In fall 2009, when Ethan Peterson ’13 arrived at MIT as an undergraduate, he already had some ideas about possible career options. He’d always liked building things, even as a child, so he imagined his future work would involve engineering of some sort. He also liked physics. And he’d recently become intent on reducing our dependence on fossil fuels and simultaneously curbing greenhouse gas emissions, which made him consider studying solar and wind energy, among other renewable sources.
Things crystallized for him in the spring semester of 2010, when he took an introductory course on nuclear fusion, taught by Anne White, during which he discovered that when a deuterium nucleus and a tritium nucleus combine to produce a helium nucleus, an energetic (14 mega electron volt) neutron — traveling at one-sixth the speed of light — is released. Moreover, 1020 (100 billion billion) of these neutrons would be produced every second that a 500-megawatt fusion power plant operates. “It was eye-opening for me to learn just how energy-dense the fusion process is,” says Peterson, who became the Class of 1956 Career Development Professor of nuclear science and engineering in July 2024. “I was struck by the richness and interdisciplinary nature of the fusion field. This was an engineering discipline where I could apply physics to solve a real-world problem in a way that was both interesting and beautiful.”
He soon became a physics and nuclear engineering double major, and by the time he graduated from MIT in 2013, the U.S. Department of Energy (DoE) had already decided to cut funding for MIT’s Alcator C-Mod fusion project. In view of that facility’s impending closure, Peterson opted to pursue graduate studies at the University of Wisconsin. There, he acquired a basic science background in plasma physics, which is central not only to nuclear fusion but also to astrophysical phenomena such as the solar wind.
When Peterson received his PhD from Wisconsin in 2019, nuclear fusion had rebounded at MIT with the launch, a year earlier, of the SPARC project — a collaborative effort being carried out with the newly founded MIT spinout Commonwealth Fusion Systems. He returned to his alma mater as a postdoc and then a research scientist in the Plasma Science and Fusion Center, taking his time, at first, to figure out how to best make his mark in the field.
Minding your neutrons
Around that time, Peterson was participating in a community planning process, sponsored by the DoE, that focused on critical gaps that needed to be closed for a successful fusion program. In the course of these discussions, he came to realize that inadequate attention had been paid to the handling of neutrons, which carry 80 percent of the energy coming out of a fusion reaction — energy that needs to be harnessed for electrical generation. However, these neutrons are so energetic that they can penetrate through many tens of centimeters of material, potentially undermining the structural integrity of components and damaging vital equipment such as superconducting magnets. Shielding is also essential for protecting humans from harmful radiation.
One goal, Peterson says, is to minimize the number of neutrons that escape and, in so doing, to reduce the amount of lost energy. A complementary objective, he adds, “is to get neutrons to deposit heat where you want them to and to stop them from depositing heat where you don’t want them to.” These considerations, in turn, can have a profound influence on fusion reactor design. This branch of nuclear engineering, called neutronics — which analyzes where neutrons are created and where they end up going — has become Peterson’s specialty.
It was never a high-profile area of research in the fusion community — as plasma physics, for example, has always garnered more of the spotlight and more of the funding. That’s exactly why Peterson has stepped up. “The impacts of neutrons on fusion reactor design haven’t been a high priority for a long time,” he says. “I felt that some initiative needed to be taken,” and that prompted him to make the switch from plasma physics to neutronics. It has been his principal focus ever since — as a postdoc, a research scientist, and now as a faculty member.
A code to design by
The best way to get a neutron to transfer its energy is to make it collide with a light atom. Lithium, with an atomic number of three, or lithium-containing materials are normally good choices — and necessary for producing tritium fuel. The placement of lithium “blankets,” which are intended to absorb energy from neutrons and produce tritium, “is a critical part of the design of fusion reactors,” Peterson says. High-density materials, such as lead and tungsten, can be used, conversely, to block the passage of neutrons and other types of radiation. “You might want to layer these high- and low-density materials in a complicated way that isn’t immediately intuitive” he adds. Determining which materials to put where — and of what thickness and mass — amounts to a tricky optimization problem, which will affect the size, cost, and efficiency of a fusion power plant.
To that end, Peterson has developed modelling tools that can make analyses of these sorts easier and faster, thereby facilitating the design process. “This has traditionally been the step that takes the longest time and causes the biggest holdups,” he says. The models and algorithms that he and his colleagues are devising are general enough, moreover, to be compatible with a diverse range of fusion power plant concepts, including those that use magnets or lasers to confine the plasma.
Now that he’s become a professor, Peterson is in a position to introduce more people to nuclear engineering, and to neutronics in particular. “I love teaching and mentoring students, sharing the things I’m excited about,” he says. “I was inspired by all the professors I had in physics and nuclear engineering at MIT, and I hope to give back to the community in the same way.”
He also believes that if you are going to work on fusion, there is no better place to be than MIT, “where the facilities are second-to-none. People here are extremely innovative and passionate. And the sheer number of people who excel in their fields is staggering.” Great ideas can sometimes be sparked by off-the-cuff conversations in the hallway — something that happens more frequently than you expect, Peterson remarks. “All of these things taken together makes MIT a very special place.”
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