Evelyn Reynolds

Before you scramble to clean your room or attempt to make your pajamas look a bit less like pajamas, here is a good excuse to keep your video off during your next virtual meeting: reducing your environmental impact. New research shows that if you turn your camera off during a videoconference, you can reduce your environmental footprint in that meeting by 96 percent.
Conducted by a team from MIT, Purdue University, and Yale University, the study uncovers the impacts that internet use has on the environment. This is especially significant considering that many countries have reported at least a 20 percent increase in internet use since March 2020 due to the Covid-19 lockdowns.
While the shift to a more digital world has made an impressive dent in global emissions overall — thanks in large part to the likely temporary emissions reductions associated with travel — the impact of our increasingly virtual lifestyles should not be overlooked.
“The goal of this paper is to raise awareness,” says Maryam Arbabzadeh, a postdoc at the MIT Energy Initiative and a co-author of the study. “It is great that we are reducing emissions in some sectors; but at the same time, using the internet also has an environmental impact contributing to the aggregate. The electricity used to power the internet, with its associated carbon, water, and land footprints, isn’t the only thing impacting the environment; the transmission and storage of data also requires water to cool the systems within them.”
One hour of streaming or videoconferencing can emit between 150 and 1,000 grams of carbon dioxide, depending on the service. By comparison, a car produces about 8,887 grams from burning one gallon of gasoline. That hour also requires 2-12 liters of water and a land area about the size of an iPad Mini. Those hours add up in our daily lives with all the time we’re spending on video — and so does the associated environmental footprint.
According to the researchers, if remote work continues through the end of 2021, the global carbon footprint could grow by 34.3 million tons in greenhouse gas emissions. To give a sense of the scale: This increase in emissions would require a forest twice the size of Portugal to fully sequester it all. Meanwhile, the associated water footprint would be enough to fill more than 300,000 Olympic-sized swimming pools, and the land footprint would be equal to roughly the size of Los Angeles.
To store and transmit all of the data powering the internet, data centers consume enough electricity to account for 1 percent of global energy demand — which is more than the total consumption for many countries. Even before the pandemic, the internet’s carbon footprint had been increasing and accounted for about 3.7 percent of global greenhouse gas emissions.
While there have been studies evaluating the carbon footprint of internet data transmission, storage, and use, the associated water and land footprints have been largely overlooked. To address this gap, the researchers in this study analyze the three major environmental footprints — water, land, and carbon — as they pertain to internet use and infrastructure, providing a more holistic look at environmental impact. Their findings are published in Resources, Conservation and Recycling.
Using publicly available data, the researchers give a rough estimate of the carbon, water, and land footprints associated with each gigabyte of data used in common online apps such as Netflix, Instagram, TikTok, Zoom, and 14 other platforms, as well as general web surfing and online gaming. They find that the more video used, the higher the footprints.
A common streaming service, like Netflix or Hulu, requires 7 gigabytes per hour of high-quality video streaming, translating to an average of 441 g CO2e (grams per carbon dioxide equivalent) per hour. If someone is streaming for four hours a day at this quality for a month, the emissions rise to 53 kg CO2e. However, if that person were to instead stream in standard definition, the monthly footprint would only be 2.5 kg CO2e. That decision would save emissions equivalent to driving a car from Baltimore, Maryland to Philadelphia, Pennsylvania, about 93 miles.
Now multiply these savings across 70 million users all streaming in standard definition rather than high definition. That behavioral change would result in a decrease of 3.5 million tons of CO2e — equating to the elimination of 1.7 million tons of coal, which is about 6% of the total monthly consumption of coal in the United States.
“Banking systems tell you the positive environmental impact of going paperless, but no one tells you the benefit of turning off your camera or reducing your streaming quality. So, without your consent, these platforms are increasing your environmental footprint,” says Kaveh Madan, who led and directed this study while a visiting fellow at the Yale MacMillan Center.
While many service providers and data centers have been working to improve operational efficiency and reduce their carbon footprints by diversifying their energy portfolios, measures still need to be taken to reduce the footprint of the product. A streaming service’s video quality is one of the largest determinants of its environmental footprint. Currently, the default for many services is high-definition, putting the onus on the user to reduce the quality of their video in order to improve their footprint. Not many people will be interested in reducing their video quality, especially if the benefits of this action are not well known.
“We need companies to give users the opportunity to make informed, sustainable choices,” says Arbabzadeh. “Companies could change their default actions to lead to less environmental impact, such as setting video quality to standard definition and allowing users to upgrade to high definition. This will also require policymakers to be involved — enacting regulations and requiring transparency about the environmental footprint of digital products to encourage both companies and users to make these changes.”
The researchers also look at specific countries to understand how different energy systems impact the environmental footprints for an average unit of energy used in data processing and transmission. The data show wide variation in carbon, land, and water intensity. In the United States, where natural gas and coal make up the largest share of electricity generation, the carbon footprint is 9 percent higher than the world median, but the water footprint is 45 percent lower and the land footprint is 58 percent lower. Meanwhile, in Brazil, where nearly 70 percent of the electricity comes from hydropower, the median carbon footprint is about 68 percent lower than the world median. The water footprint, on the other hand, is 210 percent higher than the world median, and increasing reliance on hydropower at the expense of fragile rainforest ecosystems has other substantial environmental costs.
“All of these sectors are related to each other,” says Arbabzadeh. “In data centers where electricity comes from a cleaner source, the emissions will be lower; and if it’s coming from fossil fuels, then the impact will be higher.”
“Right now, we have virtual meetings all over, and we’re spending more of our leisure time than ever streaming video content. There is definitely a paradigm shift,” she adds. “With some small behavior changes, like unsubscribing from junk emails or reducing cloud storage, we can have an impact on emissions. It is important that we raise public awareness so that, collectively, we can implement meaningful personal and systemic changes to reduce the internet’s environmental impact and successfully transition to a low-carbon economy.”
The study was supported by the MIT Energy Initiative, Purdue Climate Change Research Center, the Purdue Center for the Environment, and the Yale MacMillan Center. More

Climate action is among the top priorities for the Institute and one that demands global solutions. With Denmark’s reputation as a leader in sustainable thinking, finding a way to bring the two together presented a natural synergy for the MIT-Denmark program. Part of MIT International Science and Technology Initiatives (MISTI), MIT-Denmark connects students and faculty with institutions and industry in Denmark to advance critical research, build new technologies, and create innovative partnerships. Despite the recent challenges due to pandemic-imposed travel restrictions, developing these meaningful international collaborations continues to be a top priority for both MIT students and their counterparts abroad.
The Green Campus Challenge was launched with these goals in mind, tasking student teams to develop proposals to make a more sustainable campus and also broaden their cross-cultural competencies and learn about how sustainability is perceived in another culture.
“We need to work together to make our future more sustainable, and our campuses are the perfect place to start,” says Madeline Smith, program manager for MIT-Denmark. Smith hosted the event alongside the Confederation of Danish Industry (Dansk Industri) with additional collaboration from the MIT Office of Sustainability and the MIT Design for America Club. In the challenge, students ideated solutions and developed plans to make their university campus more sustainable within the areas of architecture/community spaces, energy, and food/waste. They tackled these issues from a global perspective, working in teams that included both MIT and Danish university students.
MIT students joining the challenge came from a variety of class years and majors, from first-year students to PhD candidates, with interests ranging from computer science to civil engineering to urban planning. Danish university students came from top universities across the country, including Aalborg University (AAU), Copenhagen Business School (CBS), the Technical University of Denmark (DTU), University of Copenhagen (KU), and Southern Denmark University (SDU).
Beyond science and technology
Challenge organizers enhanced the experience by providing student teams with mentorship from campus stakeholders, experts in academia and entrepreneurship, and some of Denmark’s most innovative companies. Danfoss advised students on district energy solutions, while mentors from KU and MIT Office of Sustainability provided information about food and waste systems. Other mentors included representatives from Rambøll, SPACE10, Blue Lobster, EcoTree, and DTU Skylab.
“Working on this event was very exciting for us,” says Miha Bobič, vice president of business development and product portfolio at Danfoss, who joined the Green Campus Challenge both as a mentor and on the jury for finalist pitches. “Due to current circumstances, we could not get the experience of face-to-face meetings and mentorship, but students still showed a great deal of engagement and developed innovative ideas, which, if properly developed, could end up as new startups.”
In between mentorship and team brainstorming, there were workshops to help students develop innovative thinking processes, consider project stakeholders, and learn how to pitch their idea to a sustainability-minded audience. Students found time for some fun as well and joined together for MIT and Denmark-themed trivia, yoga, and even a food waste-preventing cooking class organized by Danish startup, Too Good To Go.  
“It was a great experience diving into ideation, collaborating with our international teammates, learning more about their culture and approach to innovation and sustainability,” says Allison Lee, a master of city planning candidate at MIT.
The event culminated with teams presenting their pitches to a panel of judges from the U.S. and Denmark, including Franklin Carrero-Martinez (U.S. National Academy of Sciences, Engineering, and Math), Kinga Christensen (Dansk Industri), Susy Jones (MIT Sustainability), and Tomas Refslund Poulsen (KU Green Campus Initiative), as well as a jury from Danfoss, which selected a winner to recognize within the field of energy innovation.
“It was inspiring to see talented students from MIT and Danish universities pitching their ideas to create sustainable campuses for the future,” says Kinga Christensen, deputy director general for the Confederation of Danish Industry. “By bringing together their skills and perspectives, alongside the mentorship they received from Danish companies and university experts, they were able to develop some truly innovative sustainability proposals.”
Teams find winning solutions
Winning the grand prize was team Green-(In)-Spire, who proposed a campus sustainability world fair. Their plan would include a designated space on campus to showcase technologies and inventions that address campus sustainability through events and “world fairs.” The team members were Allison Lee (MIT), Anna Worning (AAU), Erik Koors (SDU), John Liu (MIT), and Kiara Wahnschafft (MIT).
Team FreeCyclers received runner-up honors for their idea to create a centralized freecycle space. This space would allow students to donate and pick up items too good to throw away, such as books, kitchen equipment, clothing, and more. The team included Eva Smerekanych (MIT), Isabel Dolp (CBS), Niklas Ludvigsen (CBS), Melissa Møller (AAU), and Shristi Rijal (SDU).
For innovations in energy, the Danfoss Prize was awarded to the team UniGreen Farmers for their idea to develop UniGreen Farms, university-led urban rooftop research facilities where interdisciplinary research could take place between senior and entry-level researchers and students. Team members were Brian Li (MIT), Federico D’Ascanio (KU), Frederik Bøllingtoft (AAU), Julia Romero (KU), and Kosmas Subashi (KU).
“This pandemic hasn’t made international collaboration easy,” says Smith. “But seeing students from MIT and Danish universities finish the Green Campus Challenge both eager to make a sustainability impact on their campus community and excited about the international network they’ve developed demonstrates the value of these types of cross-cultural experiences.”
With support from the Danish Industry Foundation and the Confederation of Danish Industry, MIT-Denmark connects MIT students and faculty with institutions and industry in Denmark. MISTI’s global experiential learning programs are made possible through the generosity of individuals, corporations, and foundations. For more information, email misti@mit.edu or contact country program managers directly. MISTI is an experiential program in the Center for International Studies within the School of Humanities, Arts, and Social Sciences. More

The King Climate Action Initiative (K-CAI), a research and policy initiative of MIT’s Abdul Latif Jameel Poverty Action Lab (J-PAL), announced the results of its first competition aimed at identifying and scaling innovative solutions at the intersection of poverty and climate change. K-CAI will fund 10 research studies to generate evidence and four projects that will take evidence-informed approaches to scale. 
Launched in July 2020 in partnership with King Philanthropies, the $25 million initiative is among the first major climate change initiatives focused on generating evidence in real-world settings, and translating that evidence into effective solutions at the nexus of climate change and poverty alleviation worldwide. 
K-CAI’s inaugural competition comes at a pivotal movement in the fight against climate change. The Biden administration recently took executive action to address climate change, including issuing a memorandum to promote evidence-informed decision-making. This action signals a renewed vigor to fight the climate crisis from the United States, and there is hope for greater global cooperation and focus on scientific evidence. 
Without urgent and collective efforts, the effects of climate change will be felt more deeply, particularly by people experiencing extreme poverty. Climate solutions need to not only reduce emissions and pollution, but also address adaption and energy access challenges to protect the most vulnerable populations.
“At King Philanthropies, we aim to improve the lives of the world’s poorest people by supporting high-performing leaders and organizations that are pursuing evidence-based strategies,” says Kim Starkey, president and CEO of King Philanthropies. “Today, climate change is worsening the problem of extreme poverty. We welcome this opportunity to work with the King Climate Action Initiative at J-PAL in identifying and scaling effective solutions that address these two crises simultaneously.”
There is still a critical lack of research on the real-world impacts of climate solutions. Lab-generated evidence can fail to account for human behavior, such as imperfect implementation or low take-up. To ensure the most effective solutions are scaled, investments in real-world evaluations are crucial.  
K-CAI addresses this research need by funding randomized evaluations that will generate rigorous evidence and catalyze the scale-up of effective climate policy and technology solutions. To that end, winners of the first competition are addressing urgent policy priorities across K-CAI’s four main focus areas: climate change mitigation, pollution reduction, adaption, and energy access. 
Climate change mitigation
In order to mitigate the worst effects of climate change, we must significantly reduce global greenhouse gas emissions. The adoption of innovative technologies or increased efficiencies can reduce industrial emission intensity and its harmful effects. One K-CAI-funded study led by Robert Metcalfe, J-PAL affiliate and visiting associate professor in economics at the University of Southern California, is dedicated to reducing greenhouse gas emissions in the shipping industry will evaluate whether changing management practices can increase fuel efficiency in the shipping industry. 
There is also a significant opportunity to reduce emissions through conservation and reduced deforestation. Adapting lessons from a previous randomized evaluation that examined the impacts of paying farmers to reduce deforestation in Uganda, K-CAI is funding a scale-up project led by Seema Jayachandran ’93, J-PAL Gender sector co-chair and professor of economics at Northwestern University; Santiago Izquierdo-Tort, ecological economist at Instituto Tecnológico Autónomo de México; and Santiago Saavedra, assistant professor of economics at Universidad del Rosario that aims to improve the cost-effectiveness of a similar program in Mexico by encouraging participants to enroll more of their eligible land.
Pollution reduction
Local pollutants, such as particulate matter, have harmful effects on health and productivity. Building on evidence from a 2019 randomized evaluation in Gujarat, India, a new project led by Michael Greenstone, J-PAL Energy, Environment, and Climate Change sector co-chair and Milton Friedman Professor of Economics at the University of Chicago; Rohini Pande, J-PAL Political Economy and Governance sector co-chair, professor of economics, and director of the Economic Growth Center at Yale University; Nick Ryan PhD ’12, J-PAL affiliate and assistant professor of economics at Yale University; and Anant Sudarshan, South Asia director at the Energy Policy Institute at the University of Chicago will support regulators in piloting and scaling an emissions trading program to incentivize reducing air pollutants in Punjab and Gujarat. The goal of this effort is to reduce pollution and make it more affordable for businesses to comply with environmental regulations. 
Similarly, K-CAI is funding a study with Douglas Almond, professor of economics and international and public affairs at Columbia University and Shuang Zhang, associate professor of economics at the University of Colorado at Boulder to leverage monitoring systems that provide objective and real-time emissions data to improve environmental inspections in China. The aim of this study is to understand if, when provided with better emissions data, environmental inspectors can improve enforcement and reduce industrial air pollution. 
Climate change adaptation
Climate change is increasing the frequency and severity of extreme weather events, from wildfires to hurricanes to droughts and floods. Increasing resilience to these extreme weather events is critical, especially for low-income communities and countries. 
A new K-CAI-funded study led by Rohini Pande and Maulik Jagnani, assistant professor of economics at the University of Colorado at Denver addresses this challenge through the first randomized evaluation of a flood early warning system in India, which will leverage forecasting and alerting systems, as well as grassroots volunteers trained in community outreach. This will generate insights on how to disseminate time-sensitive forecasts that encourage behavior that protects individuals from flood risks, despite the high initial costs of those behaviors.
Energy access
As economies in low- and middle-income countries grow, so will energy demand. The city of Cape Town, South Africa, is currently facing this challenge and exploring evidence-informed policy solutions.  
Cape Town provides free basic electricity to low-income households and has committed to net carbon neutrality by 2050. The city government must balance equitable growth goals with demand for utilities, but has limited tools at its disposal. A new scale-up project, led by B. Kelsey Jack, J-PAL Energy, Environment, and Climate Change sector co-chair and associate professor of environmental and development economics at the University of California at Santa Barbara, will adapt evidence on targeting to improve the delivery of electricity subsidies to low-income households in Cape Town, building on long-term partnerships between J-PAL Africa, Jack, and the local government. 
Next steps for climate solutions
Funding these projects is a critical first step in developing long-term, evidence-based, and effective climate change solutions focused on both mitigation and adaptation.
“Evidence-informed solutions are critical in the global fight against climate change, and K-CAI’s first round of competition winners demonstrate that it is possible to rigorously evaluate climate policies in real-world settings,” said Iqbal Dhaliwal, global executive director of J-PAL.
These studies and scaling projects utilize an innovative combination of high- and low-tech solutions in order to adapt climate solutions to low- and middle-income country contexts. Not only is this technological innovation key, but their focus on enabling policies is equally important to ensuring solutions are both effective and equitable. K-CAI-funded researchers will work with regulators, companies, and utilities to learn about program effectiveness as they take policy action.
Claire Walsh, project director of K-CAI, notes, “Policy innovation and evaluation, just like technological innovation, is vital for confronting climate change. It can help build the case for policy action and ensure that good technologies achieve their ultimate goals.” 
K-CAI will run two competitions each year to further its mission to identify, generate, and scale cost-effective solutions across its four focus areas. 
To stay up to date with environment, energy, and climate change research and policy, subscribe to J-PAL newsletters and select “Environment & Energy” as an interest area. More

Electricity generated by fusion power plants could play an important role in decarbonizing the U.S. energy sector by mid-century, says a new consensus study report from the National Academies of Sciences, Engineering, and Medicine, which also lays out for the first time a set of technical, economic, and regulatory standards and a timeline for a U.S. fusion pilot plant that would begin producing energy in the 2035-40 time frame.
To achieve this key step toward commercialization, the report calls for an aggressive public-private effort to produce by 2028 a pilot plant design that can, when built, accommodate any of the developmental approaches seeking to realize fusion’s potential as a safe, carbon-free, on-demand energy source.
These include what it calls the “leading fusion concept, a deuterium-tritium fueled tokamak,” like that being pursued at MIT spinout Commonwealth Fusion Systems (CFS) with support from the Institute’s Plasma Science and Fusion Center (PSFC) and Department of Nuclear Science and Engineering. Martin Greenwald, deputy director of the PSFC, notes that “the report can be seen as confirming and validating the vision that motivated the founding of CFS in 2018.” The new report follows and extends a 2018 National Academies study that (while acknowledging the significant scientific and technical challenges still faced by fusion) saw promise in the tokamak approach, called for continued U.S. participation in the international ITER fusion experiment, and suggested a pilot plant effort .
PSFC director and Hitachi America Professor of Engineering Dennis Whyte helped develop the new study as a member of the National Academies’ Committee on the Key Goals and Innovation Needed for a U.S. Fusion Pilot Plant, which also included representatives from other universities, national laboratories, and private companies. It sought out a broad range of expertise from government, academic, and private-sector sources, including U.S. utilities and energy companies.  
“The biggest thing,” says Whyte, is that the diverse group “came to a consensus that fusion is relevant, and that this effort is important.” Driving factors include utility industry commitments to deep cuts in carbon emissions in coming decades, along with a combination of simultaneous synergistic advances in fusion science and technology, application of new resources from areas outside the traditional fusion community, and particularly the rise of interest in private fusion developers like CFS, which collectively have received some $2 billion in funding in recent years.
There has also been a broad pivot by much of the nation’s fusion research community away from a focus on science and toward a mission of practical energy production. This consensus was expressed in a recent report by the Federal Energy Sciences Advisory Committee (FESAC) that urged the nation to “move aggressively toward the deployment of fusion energy, which could substantially power modern society while mitigating climate change,” and suggested development of a pilot plant. The new National Academies study advances the concept with specifics on what a successful pilot plant would look like.
The report’s authors took a marketplace-driven approach to defining the pilot plant’s characteristics, based on discussions with utilities and other energy-sector organizations that would ultimately be the builders, owners, and operators of fusion generating facilities, says Whyte. “Setting those goal posts is very important, laying out the technical, regulatory, and economic performance requirements for the pilot plant,” he explains. “They’re demanding, but they should be, because that’s what’s needed to make fusion viable.”
Those requirements include a total pilot plant cost of less than $5-6 billion and generating capacity of at least 50 megawatts. In addition to proving the ability to create reliable, sustained net energy gain and power production from fusion for steadily increasing periods of time, says the report, the plant must provide “cost certainty to the marketplace in terms of capital cost, construction time, control of radioactive effluents including tritium, the cost of electricity, and the maintenance/operating schedule and cost.”
These results would inform subsequent construction of first-of-a-kind commercial fusion plants in the 2040s, and then broader propagation of fusion energy facilities onto the grid around mid-century, by which time major U.S. utilities have committed to deep reductions in their carbon emissions.
A key near-term factor in achieving these goals is formation of multiple public-private teams to conceptualize and design aspects of the pilot plant over the next seven years. These include improved fusion confinement and control, materials that can withstand the withering temperatures and stresses produced during fusion, methods of extracting fusion-generated heat and harnessing it for generation, and development of a closed fuel cycle. All are technically challenging and also require close attention to cost, manufacturability, maintainability, and other system-level considerations.
Combining resources from national labs, academic institutions, and private industry is a good approach to addressing these tasks, says Martin Greenwald, deputy director of the PSFC and senior research scientist. “Technologies like fusion come to market through the private sector, especially in the U.S., and once you understand that you can see appropriate roles for government labs that can do basic research, universities that are free to work with private industry, and companies that can use their own capital to pick up and commercialize the work.” Private space programs provide an example, he notes, with companies building rockets and using NASA facilities for things like testing and launch.
“The question,” adds Greenwald, “is whether we can collectively gather the resources and investments and execute in a way that meets the pace. We don’t want to be complacent about how audacious this is, but we have to be audacious if we’re going to meet the need.”
Bob Mumgaard, chief executive officer of CFS, says the new report is another indication of fusion’s growing momentum. In addition to the two National Academies studies, growing private investment, and FESAC’s community-driven recommendations, he points to the January enactment of federal appropriations legislation that funded both domestic and international fusion activities, including ongoing participation in ITER.
“For first time in 40 years, the U.S. government has a policy of building a new energy industry, a whole ecosystem,” says Mumgaard. “The legislation sort of pre-authorized many of the things the National Academies report says are good ideas, like the pivot into energy technology, the more-aggressive timeline, and getting regulation sorted out, which is going pretty well, actually — that’s all in the bill. It lays the groundwork for the broad community to take all this to heart and start doing the work. It’s very different from isolated companies doing their own thing, and universities running experiments, and has been very rapid in terms of how these things usually go. We are entering a whole new era for fusion.”
Cecil and Ida Green Professor Emeritus Ernest Moniz, who served as U.S. secretary of energy during the Obama administration, adds that “The academy report alerts the scientific community, the Congress, and the Biden Administration, which is prioritizing climate change risk mitigation, to the incredible progress over the last years towards fusion as a viable energy source — innovation along several technology pathways, supported largely by private capital. Public-private partnerships can help take several of these technologies to demonstrations in this decade, allowing fusion to be a critical enabler of a decarbonized electric grid before mid-century.” More

Perovskites are a leading candidate for eventually replacing silicon as the material of choice for solar panels. They offer the potential for low-cost, low-temperature manufacturing of ultrathin, lightweight flexible cells, but so far their efficiency at converting sunlight to electricity has lagged behind that of silicon and some other alternatives.
Now, a new approach to the design of perovskite cells has pushed the material to match or exceed the efficiency of today’s typical silicon cell, which generally ranges from 20 to 22 percent, laying the groundwork for further improvements.
By adding a specially treated conductive layer of tin dioxide bonded to the perovskite material, which provides an improved path for the charge carriers in the cell, and by modifying the perovskite formula, researchers have boosted its overall efficiency as a solar cell to 25.2 percent — a near-record for such materials, which eclipses the efficiency of many existing solar panels. (Perovskites still lag significantly in longevity compared to silicon, however, a challenge being worked on by teams around the world.)
The findings are described in a paper in the journal Nature by recent MIT graduate Jason Yoo PhD ’20, professor of chemistry and Lester Wolfe Professor Moungi Bawendi, professor of electrical engineering and computer science and Fariborz Maseeh Professor in Emerging Technology Vladimir Bulović, and 11 others at MIT, in South Korea, and in Georgia.
Perovskites are a broad class of materials defined by the fact that they have a particular kind of molecular arrangement, or lattice, that resembles that of the naturally occurring mineral perovskite. There are vast numbers of possible chemical combinations that can make perovskites, and Yoo explains that these materials have attracted worldwide interest because “at least on paper, they could be made much more cheaply than silicon or gallium arsenide,” one of the other leading contenders. That’s partly because of the much simpler processing and manufacturing processes, which for silicon or gallium arsenide requires sustained heat of over 1,000 degrees Celsius. In contrast, perovskites can be processed at less than 200 C, either in solution or by vapor deposition.
The other major advantage of perovskite over silicon or many other candidate replacements is that it forms extremely thin layers while still efficiently capturing solar energy. “Perovskite cells have the potential to be lightweight compared to silicon, by orders of magnitude,” Bawendi says.
Perovskites have a higher bandgap than silicon, which means they absorb a different part of the light spectrum and thus can complement silicon cells to provide even greater combined efficiencies. But even using only perovskite, Yoo says, “what we’re demonstrating is that even with a single active layer, we can make efficiencies that threaten silicon, and hopefully within punching distance of gallium arsenide. And both of those technologies have been around for much longer than perovskites have.”
One of the keys to the team’s improvement of the material’s efficiency, Bawendi explains, was in the precise engineering of one layer of the sandwich that makes up a perovskite solar cell — the electron transport layer. The perovskite itself is layered with a transparent conductive layer used to carry an electric current from the cell out to where it can be used. However, if the conductive layer is directly attached to the perovskite itself, the electrons and their counterparts, called holes, simply recombine on the spot and no current flows. In the researchers’ design, the perovskite and the conductive layer are separated by an improved type of intermediate layer that can let the electrons through while preventing the recombination.
This middle electron transport layer, and especially the interfaces where it connects to the layers on each side of it, tend to be where inefficiencies occur. By studying these mechanisms and designing a layer, consisting of tin oxide, that more perfectly conforms with those adjacent to it, the researchers were able to greatly reduce the losses.
The method they use is called chemical bath deposition. “It’s like slow cooking in a Crock-Pot,” Bawendi says. With a bath at 90 degrees Celsius, precursor chemicals slowly decompose to form the layer of tin dioxide in place. “The team realized that if we understood the decomposition mechanisms of these precursors, then we’d have a better understanding of how these films form. We were able to find the right window in which the electron transport layer with ideal properties can be synthesized.”
After a series of controlled experiments, they found that different mixtures of intermediate compounds would form, depending on the acidity of the precursor solution. They also identified a sweet spot of precursor compositions that allowed the reaction to produce a much more effective film.
The researchers combined these steps with an optimization of the perovskite layer itself. They used a set of additives to the perovskite recipe to improve its stability, which had been tried before but had an undesired effect on the material’s bandgap, making it a less efficient light absorber. The team found that by adding much smaller amounts of these additives — less than 1 percent — they could still get the beneficial effects without altering the bandgap.
The resulting improvement in efficiency has already driven the material to over 80 percent of the theoretical maximum efficiency that such materials could have, Yoo says.
While these high efficiencies were demonstrated in tiny lab-scale devices, Bawendi says that “the kind of insights we provide in this paper, and some of the tricks we provide, could potentially be applied to the methods that people are now developing for large-scale, manufacturable perovskite cells, and therefore boost those efficiencies.”
In pursuing the research further, there are two important avenues, he says: to continue pushing the limits on better efficiency, and to focus on increasing the material’s long-term stability, which currently is measured in months, compared to decades for silicon cells. But for some purposes, Bawendi points out, longevity may not be so essential. Many electronic devices such as cellphones, for example, tend to be replaced within a few years anyway, so there may be some useful applications even for relatively short-lived solar cells.
“I don’t think we’re there yet with these cells, even for these kind of shorter-term applications,” he says. “But people are getting close, so combining our ideas in this paper with ideas that other people have with increasing stability could lead to something really interesting.”
Robert Hoye, a lecturer in materials at Imperial College London, who was not part of the study, says, “This is excellent work by an international team.” He adds, “This could lead to greater reproducibility and the excellent device efficiencies achieved in the lab translating to commercialized modules. In terms of scientific milestones, not only do they achieve an efficiency that was the certified record for perovskite solar cells for much of last year, they also achieve open-circuit voltages up to 97 percent of the radiative limit. This is an astonishing achievement for solar cells grown from solution.”
The team included researchers at the Korea Research Institute of Chemical Technology, the Korea Advanced Institute of Science and Technology, the Ulsan National Institute of Science and Technology, and Georgia Tech. The work was supported by MIT’s Institute for Soldier Nanotechnology, NASA, the Italian company Eni SpA through the MIT Energy Initiative, the National Research Foundation of Korea, and the National Research Council of Science and Technology. More

“That was your warmup. Now we’re really in the thick of it.” 
Daniel Korsun ’20 is reflecting on his four years of undergraduate preparation and research at MIT as he enters “the thick” of graduate study at the Institute’s Plasma Science and Fusion Center (PSFC). The nuclear science and engineering student’s “warmup” included enough fusion research on the SPARC tokamak to establish him as part of the PSFC community.
“I already have this network of peers and professors and staff,” he notes with enthusiasm. “I’ve been kind of training for this for four years.”
Korsun arrived on the MIT campus in 2016 prepared to focus on chemistry, but quickly developed a fascination for the nuclear side of physics. Postponing one of his undergraduate course requirements, he indulged in Professor Mike Short’s Introduction to Nuclear Science class. After that he was “super hooked,” especially by the subject of fusion, a carbon-free, potentially endless source of energy.
Learning from his class colleague Monica Pham ’19 about a summer Undergraduate Research Opportunity Program (UROP) opening at the PSFC, Korsun applied and quickly found himself in the center’s accelerator laboratory, which is co-operated jointly with the Department of Nuclear Science and Engineering (NSE).
“I’ve always been interested in clean energy, advanced solar, climate change. When I actually got into the depths of fusion, seeing what the PSFC was doing — nothing ever compared.”
Korsun’s continuing excitement for research at the PSFC ultimately landed him in MIT’s SuperUROP undergraduate research program during his junior year. Guided by NSE Assistant Professor Zach Hartwig and his graduate students, Korsun was learning about the fusion research that remains his focus today, including SPARC, a next-generation fusion experiment that is prototype to a planned energy-producing fusion furnace called ARC.
Both these tokamak designs are being developed by MIT in association with Commonwealth Fusion Systems (CFS), and are dependent on game-changing, high-temperature superconducting (HTS) tape. Magnets created from this tape will wrap around the tokamak’s donut-shaped vacuum chamber, confining the hot plasma.
Korsun is exploring the effect of radiation, produced during the fusion process, on the HTS tapes. To do this he needs to test the critical current of the tapes, the maximum amount of current a superconductor can conduct while remaining in a superconducting state. Because radiation damage impacts how well superconductors can carry current, the critical current of the tapes changes in relation to how much they are irradiated.
“You can irradiate anything at room temperature,” he notes. “You just blast it with protons or neutrons. But that information is not really useful, because your SPARC and ARC magnets will be at cryogenic temperatures, and they’ll be operating in extremely strong magnetic fields as well. What if these low temperatures and high fields actually impact how the material responds to damage?”
Pursuing this question as an undergraduate took him with his teammates as far as Japan and New Zealand, where they could use special facilities to test the critical current of HTS tape under relevant conditions. “On our Japan trip to the High Field Laboratory for Superconducting Materials at Tohoku University, we conducted the SPARC project’s first-ever tests of HTS tape at the actual SPARC toroidal field magnetic field and temperature. It was a grueling trip — we generally worked about 15 or 16 hours a day in the lab — but incredible.”
The necessity of leaving campus in the spring of his senior year due to the Covid lockdown meant that Korsun would graduate virtually.
“It was not ideal. I’m not the kind of person to sit on my parents’ couch for six months.”
He made the most of his summer by securing a virtual internship at CFS, where he helped to refine ARC’s design based on what had been learned from SPARC research.
“Crazy amounts of knowledge have been gained that were not even fathomable five years ago, when it was designed.”
Korsun looks forward to the day when SPARC is operating, inspiring even more updates to the ARC design.
“It’s so easy to get excited about SPARC,” he says. “Everyone is, and I am, too. But it’s not quite the end goal. We’ve got to keep an eye on the distance.” More

Pablo Duenas-Martinez and Dharik Mallapragrada first met on opposite sides of a sponsored research project through the MIT Energy Initiative (MITEI). They worked together to define a project to study the long-term evolution of the electricity sector in India and the impacts of technological and policy drivers. Duenas-Martinez guided the research direction on MITEI’s end, and Mallapragada provided input from an industry perspective.
Mallapragada, who earned his PhD in chemical engineering from Purdue University, had been working in the energy and petrochemical sector for about five years at two different companies when he came to a realization.
“As I took on a bunch of different roles at the companies, I came to realize the connections between the applied research I was pursuing and the policy implications in the context of decarbonizing energy systems, but somehow the framing of the problems I was investigating didn’t sit right with me,” he says. He came to MIT because he wanted to think about the issue in broader terms. “The main challenge in my mind is to address economy-wide decarbonization while simultaneously expanding access to energy. It is not just the end state, but the entire trajectory of this transition that matters. I think everybody recognizes what the end goal is. But there are no real clear pathways that have been identified, and I’ve been eager to contribute toward addressing the gaps in this area of energy research.”
At MITEI, Mallapragada utilizes his engineering training and industry background while learning about all the other elements that are necessary to be able to address the grand challenge of decarbonization, which he describes as “really very multidisciplinary in terms of scope and applications.”
Mallapragada joined fellow research scientists Duenas-Martinez and Karen Tapia-Ahumada at the Electric Power Systems (EPS) Center, one of MITEI’s Low-Carbon Energy Centers. The center unites MIT researchers, faculty, and students to accelerate the transition to a clean electric power sector. The center’s mission is threefold:
to examine the impacts of emerging technologies, business models, regulatory frameworks, and policy dynamics;
to investigate solutions ranging from developing new analytical tools for improved decision-making in the industry to vetting breakthrough technologies; and
to serve as a convening entity to engage industry and policymakers and provide thought leadership through rigorous analysis of the clean energy transition.
Steering EPS Center projects
Mallapragada, Duenas-Martinez, and Tapia-Ahumada all bring a wealth of experience to their roles as the researchers who shape the direction of EPS Center projects. Mallapragada, the newest addition to the team, credits his previous work in the energy industry and personal experience working with academia on sponsored projects with helping him to “hit the ground running” at MITEI, in terms of engaging with research sponsors and guiding projects.
“Oftentimes, research scientists become conduits for communication within an organization. Our research helps people from different sides of the business engage with each other in new ways,” says Mallapragada. “Our role is not just to do the research, but actually to persuade people to think about problems and challenges in new ways, using evidence generated from modeling and analysis.”
Duenas-Martinez is no stranger to helping people in different sectors — from power and gas utilities to government and regulatory agencies — think outside the box to improve energy systems around the world.
He grew up in Madrid, where he obtained his bachelor’s degree in industrial engineering, a master’s in electric power systems, and a doctorate in electrical engineering at Comillas Pontifical University. He first came into contact with MIT during his PhD work in 2012, before joining MITEI as a postdoc in 2014. “I also received a bachelor’s in economics from a distance learning university two years ago,” he says.
A number of his projects touch on the impacts of natural gas on the electric power system, but his work has started moving in a different direction. “Lately, I’ve been working on the security of energy supply and researching the distribution side and all the changes that are happening in the electric power system,” says Duenas-Martinez.
Tapia-Ahumada, an electrical engineer, joined MITEI as a postdoc in 2011 and became a research scientist in 2014, but she has been at MIT for far longer. Like Mallapragada and Duenas-Martinez, her journey to MITEI spans years and continents. She grew up in Chile and came to MIT in 2003 after living and working in Argentina following her graduation from the Pontifical Catholic University of Chile.
While her husband pursued his MBA, Tapia-Ahumada was accepted into MIT’s Technology and Policy Program, where she completed her graduate degree and continued on to earn her PhD in engineering systems.
“I did both my master’s and PhD while I was having my kids — so I finished everything all at once,” she says. Tapia-Ahumada completed postdoc work at MIT and finally landed at MITEI as a research scientist. “It has been a long and a rewarding road for me here at MIT,” she says.
Tapia-Ahumada’s research interests include the operation and planning of electric power systems, renewable energy generation, distributed energy resources, and the market and regulatory structures required to support the development of sustainable energy systems.
Roles at MITEI
Mallapragada, Duenas-Martinez, and Tapia-Ahumada manage separate projects and teams within the EPS Center’s portfolio, but they utilize their different backgrounds to work toward the common goal of implementing widespread electricity access while decarbonizing the electric power sector.
They each define their role slightly differently.
“In some ways, I play the role of a principal investigator on a research project, while also being fairly hands-on with the research — not only doing some of it, but also defining what the research objectives are and then working with students to meet the research goals,” says Mallapragada. He notes that he primarily works with graduate students from MIT’s Technology and Policy Program.
Duenas-Martinez concurs with Mallapragada, adding that establishing and managing the human capital for a project is a major part of sponsored research projects. “Sometimes we work together with a postdoc or a student — and sometimes, as in the cases of both Karen and me, we have even been the postdoc or the student on the project,” he says.
Of equal importance, he says, is working with international students. Students from around the world often contact MITEI research scientists about topics of interest, and MITEI will invite them to come work on a project to help enrich the EPS Center’s work with outside ideas.
They also work with “UROPs” — students who receive funding through MIT’s vast Undergraduate Research Opportunities Program, which connects students with faculty to work on new or established research projects. “My experience with UROP students has always been great,” says Duenas-Martinez. “They are motivated and very, very smart.”
Tapia-Ahumada explains that they are all very hands-on when it comes to helping students succeed. “We [research scientists] are all developing particular modeling tools, so we know the details of the tools, and then when we bring on students, we are starting from scratch. They need the extra push from us at the beginning to learn how to set up and run the models, and then, once they are up to speed, we supervise their research throughout the course of the project,” she explains.
The three research scientists also regularly serve as advisors for master’s theses, and work with postdocs to help them figure out where they’d like to end up post-MITEI.
The EPS Center researchers do not work in fixed groups on every project. In fact, Mallapragada feels fortunate to have been part of quite a few different teams working on MITEI projects. “I’ve been able to build my own network that spans across MIT, rather than having a team that I work with on a day-to-day basis. I’m kind of like a puzzle piece that fits in wherever I’m needed,” he says.
Tapia-Ahumada observes that research scientists act as a link between professors and particular projects. “Sometimes the professors provide the high-level ideas, and then we are there to help work out the smaller details of the project,” she notes.
Mallapragada says MITEI research scientists help faculty by providing greater context to, and perspective on, the fundamental research that may be happening within academic departments. “We don’t necessarily operate within the realm of technology development or fundamental science research ourselves, but we help faculty contextualize the work they are doing and make it appealing to an industrial sponsor, who may not otherwise be thinking about these issues from a long-term perspective. That is something that has an appeal not only within the electric power systems sector, but also across all the end-use sectors,” he says. “We fit into the technology development pipeline as a contact center for defining what topics need to be focused on by industry, policymakers, and academia in order to accelerate the sustainable energy transition.”
Research highlights and planned trajectories
Of the many projects they’ve participated in at MITEI, a few remain highlights. Duenas-Martinez counts MITEI’s 2016 Utility of the Future study as a particular favorite. The study addressed the technology, policy, and business models that are shaping the evolution of the delivery of electricity services.
“We were on the cutting edge of knowledge. We were doing some really deep analysis of what’s going to happen in the next few years, with all the transformation that is happening in the electric power systems,” says Duenas-Martinez. “This was a consortium project, which was something very new for me. We had 10 companies involved and also an expert advisory board, so there were long discussions with large groups about very hot topics at the time, and it was a great learning experience because I was new. It was so rewarding.”
One of Tapia-Ahumada’s favorite projects focused on Iceland. “It was fascinating because of the topic itself. Iceland’s energy is almost 100 percent renewable, so it was very interesting to learn about some of the challenges they are facing in order to ensure the long-term security of electricity supply in an economic manner while preserving environmental goals.” She also enjoyed having the opportunity to work with both Duenas-Martinez and colleagues from Comillas Pontifical University in Spain. “It was an international group of people working on a very relevant topic,” she says.
Tapia-Ahumada, along with Ignacio Pérez-Arriaga, a visiting professor from Comillas Pontifical University, also worked on a MITEI Seed Fund project with Mei Yuan, a research scientist at the Joint Program on the Science and Policy of Global Change. They developed an integrated framework that combined electricity and economic modeling with policy analysis of carbon cap-and-trade, renewable portfolio standards, and other energy and climate mechanisms used in the United States. Tapia-Ahumada says she found the project rewarding because it allowed the researchers to decide how to expand their modeling tools and determine which scenarios to analyze.
Mallapragada came on board with MITEI as part of a sponsored research project looking into the factors likely to impact the delivered cost of electricity in future low-carbon grids and the role for emerging technologies like battery energy storage. He considers it to be a highlight of his time at MITEI. “The fairly broad project scope meant that I had significant autonomy in terms of refining the research questions and approach, and it led us to identify some interesting insights on the long-term value of battery energy storage in power systems,” he says. He plans to continue pursuing research on the role that hydrogen will play in the future clean energy system — a question that has been of increasing importance during his time at MITEI. “I’ve seen a clear, increasing emphasis on opportunities for clean hydrogen, and I’ve been fortunate to get involved with a few projects, some of which have been published, but others for which the results will be coming along within the next year or so.”
According to Duenas-Martinez, the majority of the changes happening in the electric power sector are happening at the consumer level. He plans to explore how the adoption of new technologies and distributed resources is going to impact the power system in general. “I want to know how energy communities will migrate to new technologies and how consumer empowerment and choice enter into the equation. What will the future of our electric power system look like?” he asks.
“The work that we are doing at MITEI is very wide in scope, and our focus on the electric power system also encompasses electrification, which involves other sectors of the economy,” adds Tapia-Ahumada. “We are thinking hard about how to expand our research scope to incorporate other sectors, such as energy-intensive heating and transportation.”
She aims to better understand the economic signals that consumers receive and the effects of electricity retail prices. “We are exploring how the retail price of electricity could be set to result in an efficient economic response — and how on-site energy generation will affect electricity consumption.”
Tapia-Ahumada adds that she thinks of herself as a bridge between research methodology and real-world applications. “We have many methodologies, but then we need to find the right sort of abstraction in order for us to develop appropriate tools that can produce meaningful results, and then find ways to communicate those findings to nontechnical audiences so they can understand the potential applications and various pathways.”
In addition to being a research scientist, Tapia-Ahumada is MITEI’s digital learning fellow, a new role at MITEI that means she is responsible for helping develop and implement MITEI’s online course curriculum.
Researching through a pandemic
Of course, learning and research in the age of Covid-19 looks a bit different, especially for those with children at home.
“We are researchers, but we are also primarily parents of kids of various ages,” says Mallapragada. “My own personal experience has been that, on the face of it, the pandemic seems like something you can handle — but as the weeks have gone by, the situation has evolved, just like the disease.” While he is grateful for the extra time with his son, it seems like the rest of the world has “kind of normalized,” he notes.
“It’s not that anybody’s pressuring you to do things, but it’s just that you also want to normalize and work at your pre-Covid-19 pace. And so you’re kind of torn in different directions,” he says. “I feel like in some ways, it has been a lot harder now than in the beginning, when maybe you were thinking of this as a short-term thing that would soon evolve into something that resembles normalcy. So — I have mixed feelings. Obviously, there are good days and bad days,” reflects Mallapragada.
“I think we’re all parents here, so we have some personal situations at home to deal with, and we’ve also been enjoying the extra family time, but I will say that research-wise, we haven’t really scaled back much,” says Duenas-Martinez. “We have all been working equally as hard at home as when we were at the office. There are long nights, weekends are like weekdays, but overall, it’s been pretty good.”
“For me, the transition has been okay,” says Tapia-Ahumada. “My boys are already teenagers. They are very independent and they’re close in age, so they keep themselves busy.”
Tapia-Ahumada also says there has been no difference when it comes to working with research sponsors. For example, she has been working with a sponsor since before the pandemic hit that is based in both San Francisco and China.
“Before the Covid crisis, we were working with them remotely, so there have been no changes there. It has been good; they have kept collaborating with us. And they are also very conscious of our time constraints,” she says. “Everyone has been flexible, which helps because I think we’re all in the same boat — everyone understands that we have family commitments and some things that we didn’t foresee. But it’s been good. With research you always keep going — it’s never-ending.”
Energy access and communications challenges
The three also offer insights into what they consider to be the most important challenges to solve in the energy space. While decarbonization is certainly an urgent issue, the team also considers expanded energy access and the accessible, effective communication of research findings to be other major obstacles to overcome.
Duenas-Martinez says he remains focused on the long-term outlook for energy systems and on other critical problems, including how to provide reliable and affordable electricity to those who are still without power. “We still have about 1 billion people without access to good electricity. This is one topic that MITEI is focused on: We are working with the Universal Energy Access Lab to facilitate energy access to those around the globe,” says Duenas-Martinez. “We have been developing tools and we are in close contact with multilateral organizations, and governments and authorities from different countries to try to make this transformation possible.”
Another major barrier to the clean energy transition is the lack of a common language within academia. “I have different styles for working with electrical engineers versus economists. It’s very challenging to find a common language so that multidisciplinary teams can understand each other,” says Tapia-Ahumada.
In addition, it’s hard to get the research into the hands of those who can do something with it and effect real change, such as policymakers and the general public. “How do we communicate with lay people and policymakers in order for them to understand the need for decarbonization, where we are trying to go, and what we are trying to accomplish?” she asks.
Duenas-Martinez adds that he is always taken aback by how hard it is to explain what is going on in the energy world to the general public and to combat preconceived notions and pervasive misinformation: “There are many hot topics, starting with decarbonization and local air pollution, where people already have pieces of information — but it’s not always the correct information, and it has surprised me how difficult it is to explain the reality and help them to see the fuller energy picture.”
Mallapragada, too, is focused on engaging with academia, industry, policymakers, and the public in a meaningful way. “There’s an increasing demand from society for science to be relevant to social issues and making that connection — so what may not have been part of the job description of a scientist previously is now a significant part of our role. It’s not just about doing good research and publishing papers, but there is the added responsibility to take the extra step to communicate the findings effectively and in a nuanced way,” says Mallapragada.
Working the clean energy transition
Finding the balance between solving energy problems and being realistic about the best paths forward can also be a challenge.
“At the end of the day, I want to be a constructive contributor in solving climate and energy challenges. And sometimes the constructive contributor has to be the one to say, ‘Hey, we don’t have all the answers, and we need to pump the brakes. Otherwise, we might end up going down a path that we may not like down the road,’” says Mallapragada.
“We know that 2050 is the target that everyone has in mind for reaching our decarbonization goals,” adds Tapia-Ahumada. “If we are to make a successful energy transition, electricity prices will be key. We’ll keep working on our simulation tools. They are not going to be the final answer, but they will identify the various pathways that the energy or electricity sector may take. This information is going to be useful for regulators, utilities, and other stakeholders working on the transition.”
As the world continues to work toward a sustainable energy future, Duenas-Martinez says MITEI researchers will offer a set of solutions that could help move us down the path, but not dictate the path itself.
“We are not here to say what should be done. We are more here just to provide food for thought,” says Duenas-Martinez. “We are doing the analysis, we are testing different scenarios, we are innovating and developing lots of solutions. We don’t know which solution is the best one, but we are doing the best we can to try to improve our future by providing industry and policy makers with the tools to solve our energy challenges.”
This article appears in the Autumn 2020 issue of Energy Futures, the magazine of the MIT Energy Initiative.  More

The pursuit of fusion as a safe, carbon-free, always-on energy source has intensified in recent years, with a number of organizations pursuing aggressive timelines for technology demonstrations and power plant designs. New-generation superconducting magnets are a critical enabler for many of these programs, which creates growing need for sensors, controls, and other infrastructure that will allow the magnets to operate reliably in the harsh conditions of a commercial fusion power plant.
A collaborative group led by Department of Nuclear Science and Engineering (NSE) doctoral student Erica Salazar recently took a step forward in this area with a promising new method for quick detection of a disruptive abnormality, quench, in powerful high-temperature superconducting (HTS) magnets. Salazar worked with NSE Assistant Professor Zach Hartwig of the MIT Plasma Science and Fusion Center (PSFC) and Michael Segal of spinout Commonwealth Fusion Systems (CFS), along with members of the Swiss CERN research center and the Robinson Research Institute (RRI) at Victoria University in New Zealand to achieve the results, which were published in the journal Superconductor Science and Technology.
Stanching quench
Quench occurs when part of a magnet’s coil shifts out of a superconducting state, where it has no electrical resistance, and into a normal resistive state. This causes the massive current flowing through the coil, and stored energy in the magnet, to quickly convert into heat, and potentially cause serious internal damage to the coil.
While quench is a problem for all systems using superconducting magnets, Salazar’s team is focused on preventing it in power plants based on magnetic-confinement fusion devices. These types of fusion devices, known as tokamaks, will maintain a plasma at extremely high temperature, similar to the core of a star, where fusion can occur and generate net-positive energy output. No physical material can handle those temperatures, so magnetic fields are used to confine, control, and insulate the plasma. The new HTS magnets allow the tokamak’s toroidal (doughnut-shaped) magnetic enclosure to be both stronger and more compact, but interruptions in the magnetic field from quench would halt the fusion process — hence the importance of improved sensor and control capabilities.
With this in mind, Salazar’s group sought a way of quickly spotting temperature changes in the superconductors, which can indicate nascent quench incidents. Their test bed was a novel superconducting cable developed in the SPARC program known as VIPER, which incorporates assemblies of thin steel tape coated with HTS material, stabilized by a copper former and jacketed in copper and stainless steel, with a central channel for cryogenic cooling. Coils of VIPER can generate magnetic fields two-to-three times stronger than the older-generation low-temperature superconducting (LTS) cable; this translates into vastly higher fusion output power, but also makes the energy density of the field higher, which places more onus on quench detection to protect the coil.
A focus on fusion’s viability
Salazar’s team, like the entire SPARC research and development effort, approached its work with a focus on eventual commercialization, usability, and ease of manufacture, with an eye toward accelerating fusion’s viability as an energy source. Her background as a mechanical engineer with General Atomics during production and testing of LTS magnets for the international ITER fusion facility in France gave her perspective on sensing technologies and the critical design-to-production transition.
“Moving from manufacturing into design helped me think about whether what we’re doing is a practical implementation,” explains Salazar. Moreover, her experience with voltage monitoring, the traditional quench-detection approach for superconducting cable, led her to think a different approach was needed. “During fault testing of the ITER magnets, we observed electrical breakdown of the insulation occurring at the voltage tap wires. Because I now consider anything that breaks high-voltage insulation to be a major risk point, my perspective on a quench detection system was, what do we do to minimize these risks, and how can we make it as robust as possible?”
A promising alternative was temperature measurement using optical fibers inscribed with micro-patterns known as fiber Bragg gratings (FBGs). When broadband light is directed at an FBG, most of the light passes through, but one wavelength (determined by the spacing, or period, of the grating’s pattern) is reflected. The reflected wavelength varies slightly with both temperature and strain, so placement of a series of gratings with different periods along the fiber allows independent temperature monitoring of each location.
While FBGs have been leveraged across many different industries for measurement of strain and temperature, including on much smaller superconducting cables, they had not been used on larger cables with high current densities like VIPER. “We wanted to take good work by others and put it to the test on our cable design,” says Salazar. VIPER cable was well-adapted for this approach, she notes, because of its stable structure, which is designed to withstand the intense electrical, mechanical, and electromagnetic stresses of a fusion magnet’s environment.
A new extension on FBGs
A novel option was provided by the RRI team in the form of ultra-long fiber Bragg gratings (ULFBGs) — a series of 9-milimeter FBGs spaced 1 mm apart. These essentially behave as one long quasi-continuous FBG, but with the advantage that the combined grating length can be meters long instead of millimeters. While conventional FBGs can monitor temperature changes at localized points, ULFBGs can monitor simultaneously occurring temperature changes along their entire length, allowing them to provide very rapid detection of temperature variation, irrespective of the location of the heat source.
Although this means that the precise location of hot spots is obscured, it works very well in systems where early identification of a problem is of utmost importance, as in an operating fusion device. And a combination of ULFBGs and FBGs could provide both spatial and temporal resolution.
An opportunity for hands-on verification came via a CERN team working with standard FBGs on accelerator magnets at the CERN facility in Geneva, Switzerland. “They thought FBG technology, including the ULFBG concept, would work well on this type of cable and wanted to look into it, and got on board with the project,” says Salazar.
In 2019, she and colleagues journeyed to the SULTAN facility in Villigen, Switzerland, a leading center for superconducting cable evaluation operated by the Swiss Plasma Center (SPC), which is affiliated with Ecole Polytechnique Fédérale de Lausanne, to evaluate samples of VIPER cable with optical fibers set into grooves on their outer copper jackets. Their performance was compared to traditional voltage taps and resistance temperature sensors.
Quick detection under realistic conditions
The researchers were able to quickly and reliably detect small temperature disturbances under realistic operating conditions, with the fibers picking up early-stage quench growth before thermal runaway more effectively than the voltage taps. When compared to the challenging electromagnetic environment seen in a fusion device, the fibers’ signal-to-noise ratio was several times better; in addition, their sensitivity increased as quench regions expanded, and the fibers’ response times could be tuned. This enabled them to detect quench events tens of seconds faster than voltage taps, especially during slowly propagating quenches — a characteristic unique to HTS which is exceptionally difficult for voltage taps to detect in the tokamak environment, and which can lead to localized damage.
“[U]sing fiber optic technologies for HTS magnets quench detection or as a dual verification method with voltage show great promise,” says the group’s write-up, which also cites the manufacturability and minimal technological risk of the approach.
“The development of sensitive temperature measurements with FBGs is a very promising approach to the challenging problem of protecting HTS coils from damage during quenches,” observes Kathleen Amm, director of the Brookhaven National Laboratory Magnet Division, who was not affiliated with the research effort. “This is critical to the development of game-changing technologies like compact fusion, where practical, high-field, high-temperature superconducting magnets are a key technology. It also has the potential to solve the problem of quench protection for many industrial HTS applications.”
Work is underway on refining the location and installation of the fibers, including the type of adhesive used, and also on investigating how the fibers can be installed in other cables and on different platforms, says Salazar.
“We’re having a lot of dialogue with CFS and continuing to coordinate with the RRI team’s ULFBG technology, and I am currently creating a 3D model of quench dynamics, so we can better understand and predict what quench would look like under different conditions,” states Salazar. “Then we can develop design recommendations for the detection system, like the type and spacing of the gratings, so it can detect in the desired length of time. That will allow the controls engineers and the engineers working on quench detection algorithms to write and optimize their code.”
Salazar praised the experimental team’s outstanding collegiality, noting, “the collaboration with RRI and CERN was special. We all converged in Switzerland, worked hard together, and had fun putting our efforts in and getting great results.”
Funding for this research was provided by CFS. More