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    MIT-designed project achieves major advance toward fusion energy

    It was a moment three years in the making, based on intensive research and design work: On Sept. 5, for the first time, a large high-temperature superconducting electromagnet was ramped up to a field strength of 20 tesla, the most powerful magnetic field of its kind ever created on Earth. That successful demonstration helps resolve the greatest uncertainty in the quest to build the world’s first fusion power plant that can produce more power than it consumes, according to the project’s leaders at MIT and startup company Commonwealth Fusion Systems (CFS).

    That advance paves the way, they say, for the long-sought creation of practical, inexpensive, carbon-free power plants that could make a major contribution to limiting the effects of global climate change.

    “Fusion in a lot of ways is the ultimate clean energy source,” says Maria Zuber, MIT’s vice president for research and E. A. Griswold Professor of Geophysics. “The amount of power that is available is really game-changing.” The fuel used to create fusion energy comes from water, and “the Earth is full of water — it’s a nearly unlimited resource. We just have to figure out how to utilize it.”

    Developing the new magnet is seen as the greatest technological hurdle to making that happen; its successful operation now opens the door to demonstrating fusion in a lab on Earth, which has been pursued for decades with limited progress. With the magnet technology now successfully demonstrated, the MIT-CFS collaboration is on track to build the world’s first fusion device that can create and confine a plasma that produces more energy than it consumes. That demonstration device, called SPARC, is targeted for completion in 2025.

    “The challenges of making fusion happen are both technical and scientific,” says Dennis Whyte, director of MIT’s Plasma Science and Fusion Center, which is working with CFS to develop SPARC. But once the technology is proven, he says, “it’s an inexhaustible, carbon-free source of energy that you can deploy anywhere and at any time. It’s really a fundamentally new energy source.”

    Whyte, who is the Hitachi America Professor of Engineering, says this week’s demonstration represents a major milestone, addressing the biggest questions remaining about the feasibility of the SPARC design. “It’s really a watershed moment, I believe, in fusion science and technology,” he says.

    The sun in a bottle

    Fusion is the process that powers the sun: the merger of two small atoms to make a larger one, releasing prodigious amounts of energy. But the process requires temperatures far beyond what any solid material could withstand. To capture the sun’s power source here on Earth, what’s needed is a way of capturing and containing something that hot — 100,000,000 degrees or more — by suspending it in a way that prevents it from coming into contact with anything solid.

    That’s done through intense magnetic fields, which form a kind of invisible bottle to contain the hot swirling soup of protons and electrons, called a plasma. Because the particles have an electric charge, they are strongly controlled by the magnetic fields, and the most widely used configuration for containing them is a donut-shaped device called a tokamak. Most of these devices have produced their magnetic fields using conventional electromagnets made of copper, but the latest and largest version under construction in France, called ITER, uses what are known as low-temperature superconductors.

    The major innovation in the MIT-CFS fusion design is the use of high-temperature superconductors, which enable a much stronger magnetic field in a smaller space. This design was made possible by a new kind of superconducting material that became commercially available a few years ago. The idea initially arose as a class project in a nuclear engineering class taught by Whyte. The idea seemed so promising that it continued to be developed over the next few iterations of that class, leading to the ARC power plant design concept in early 2015. SPARC, designed to be about half the size of ARC, is a testbed to prove the concept before construction of the full-size, power-producing plant.

    Until now, the only way to achieve the colossally powerful magnetic fields needed to create a magnetic “bottle” capable of containing plasma heated up to hundreds of millions of degrees was to make them larger and larger. But the new high-temperature superconductor material, made in the form of a flat, ribbon-like tape, makes it possible to achieve a higher magnetic field in a smaller device, equaling the performance that would be achieved in an apparatus 40 times larger in volume using conventional low-temperature superconducting magnets. That leap in power versus size is the key element in ARC’s revolutionary design.

    The use of the new high-temperature superconducting magnets makes it possible to apply decades of experimental knowledge gained from the operation of tokamak experiments, including MIT’s own Alcator series. The new approach, led by Zach Hartwig, the MIT principal investigator and the Robert N. Noyce Career Development Assistant Professor of Nuclear Science and Engineering, uses a well-known design but scales everything down to about half the linear size and still achieves the same operational conditions because of the higher magnetic field.

    A series of scientific papers published last year outlined the physical basis and, by simulation, confirmed the viability of the new fusion device. The papers showed that, if the magnets worked as expected, the whole fusion system should indeed produce net power output, for the first time in decades of fusion research.

    Martin Greenwald, deputy director and senior research scientist at the PSFC, says unlike some other designs for fusion experiments, “the niche that we were filling was to use conventional plasma physics, and conventional tokamak designs and engineering, but bring to it this new magnet technology. So, we weren’t requiring innovation in a half-dozen different areas. We would just innovate on the magnet, and then apply the knowledge base of what’s been learned over the last decades.”

    That combination of scientifically established design principles and game-changing magnetic field strength is what makes it possible to achieve a plant that could be economically viable and developed on a fast track. “It’s a big moment,” says Bob Mumgaard, CEO of CFS. “We now have a platform that is both scientifically very well-advanced, because of the decades of research on these machines, and also commercially very interesting. What it does is allow us to build devices faster, smaller, and at less cost,” he says of the successful magnet demonstration. 

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    Proof of the concept

    Bringing that new magnet concept to reality required three years of intensive work on design, establishing supply chains, and working out manufacturing methods for magnets that may eventually need to be produced by the thousands.

    “We built a first-of-a-kind, superconducting magnet. It required a lot of work to create unique manufacturing processes and equipment. As a result, we are now well-prepared to ramp-up for SPARC production,” says Joy Dunn, head of operations at CFS. “We started with a physics model and a CAD design, and worked through lots of development and prototypes to turn a design on paper into this actual physical magnet.” That entailed building manufacturing capabilities and testing facilities, including an iterative process with multiple suppliers of the superconducting tape, to help them reach the ability to produce material that met the needed specifications — and for which CFS is now overwhelmingly the world’s biggest user.

    They worked with two possible magnet designs in parallel, both of which ended up meeting the design requirements, she says. “It really came down to which one would revolutionize the way that we make superconducting magnets, and which one was easier to build.” The design they adopted clearly stood out in that regard, she says.

    In this test, the new magnet was gradually powered up in a series of steps until reaching the goal of a 20 tesla magnetic field — the highest field strength ever for a high-temperature superconducting fusion magnet. The magnet is composed of 16 plates stacked together, each one of which by itself would be the most powerful high-temperature superconducting magnet in the world.

    “Three years ago we announced a plan,” says Mumgaard, “to build a 20-tesla magnet, which is what we will need for future fusion machines.” That goal has now been achieved, right on schedule, even with the pandemic, he says.

    Citing the series of physics papers published last year, Brandon Sorbom, the chief science officer at CFS, says “basically the papers conclude that if we build the magnet, all of the physics will work in SPARC. So, this demonstration answers the question: Can they build the magnet? It’s a very exciting time! It’s a huge milestone.”

    The next step will be building SPARC, a smaller-scale version of the planned ARC power plant. The successful operation of SPARC will demonstrate that a full-scale commercial fusion power plant is practical, clearing the way for rapid design and construction of that pioneering device can then proceed full speed.

    Zuber says that “I now am genuinely optimistic that SPARC can achieve net positive energy, based on the demonstrated performance of the magnets. The next step is to scale up, to build an actual power plant. There are still many challenges ahead, not the least of which is developing a design that allows for reliable, sustained operation. And realizing that the goal here is commercialization, another major challenge will be economic. How do you design these power plants so it will be cost effective to build and deploy them?”

    Someday in a hoped-for future, when there may be thousands of fusion plants powering clean electric grids around the world, Zuber says, “I think we’re going to look back and think about how we got there, and I think the demonstration of the magnet technology, for me, is the time when I believed that, wow, we can really do this.”

    The successful creation of a power-producing fusion device would be a tremendous scientific achievement, Zuber notes. But that’s not the main point. “None of us are trying to win trophies at this point. We’re trying to keep the planet livable.” More

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    Making the case for hydrogen in a zero-carbon economy

    As the United States races to achieve its goal of zero-carbon electricity generation by 2035, energy providers are swiftly ramping up renewable resources such as solar and wind. But because these technologies churn out electrons only when the sun shines and the wind blows, they need backup from other energy sources, especially during seasons of high electric demand. Currently, plants burning fossil fuels, primarily natural gas, fill in the gaps.

    “As we move to more and more renewable penetration, this intermittency will make a greater impact on the electric power system,” says Emre Gençer, a research scientist at the MIT Energy Initiative (MITEI). That’s because grid operators will increasingly resort to fossil-fuel-based “peaker” plants that compensate for the intermittency of the variable renewable energy (VRE) sources of sun and wind. “If we’re to achieve zero-carbon electricity, we must replace all greenhouse gas-emitting sources,” Gençer says.

    Low- and zero-carbon alternatives to greenhouse-gas emitting peaker plants are in development, such as arrays of lithium-ion batteries and hydrogen power generation. But each of these evolving technologies comes with its own set of advantages and constraints, and it has proven difficult to frame the debate about these options in a way that’s useful for policymakers, investors, and utilities engaged in the clean energy transition.

    Now, Gençer and Drake D. Hernandez SM ’21 have come up with a model that makes it possible to pin down the pros and cons of these peaker-plant alternatives with greater precision. Their hybrid technological and economic analysis, based on a detailed inventory of California’s power system, was published online last month in Applied Energy. While their work focuses on the most cost-effective solutions for replacing peaker power plants, it also contains insights intended to contribute to the larger conversation about transforming energy systems.

    “Our study’s essential takeaway is that hydrogen-fired power generation can be the more economical option when compared to lithium-ion batteries — even today, when the costs of hydrogen production, transmission, and storage are very high,” says Hernandez, who worked on the study while a graduate research assistant for MITEI. Adds Gençer, “If there is a place for hydrogen in the cases we analyzed, that suggests there is a promising role for hydrogen to play in the energy transition.”

    Adding up the costs

    California serves as a stellar paradigm for a swiftly shifting power system. The state draws more than 20 percent of its electricity from solar and approximately 7 percent from wind, with more VRE coming online rapidly. This means its peaker plants already play a pivotal role, coming online each evening when the sun goes down or when events such as heat waves drive up electricity use for days at a time.

    “We looked at all the peaker plants in California,” recounts Gençer. “We wanted to know the cost of electricity if we replaced them with hydrogen-fired turbines or with lithium-ion batteries.” The researchers used a core metric called the levelized cost of electricity (LCOE) as a way of comparing the costs of different technologies to each other. LCOE measures the average total cost of building and operating a particular energy-generating asset per unit of total electricity generated over the hypothetical lifetime of that asset.

    Selecting 2019 as their base study year, the team looked at the costs of running natural gas-fired peaker plants, which they defined as plants operating 15 percent of the year in response to gaps in intermittent renewable electricity. In addition, they determined the amount of carbon dioxide released by these plants and the expense of abating these emissions. Much of this information was publicly available.

    Coming up with prices for replacing peaker plants with massive arrays of lithium-ion batteries was also relatively straightforward: “There are no technical limitations to lithium-ion, so you can build as many as you want; but they are super expensive in terms of their footprint for energy storage and the mining required to manufacture them,” says Gençer.

    But then came the hard part: nailing down the costs of hydrogen-fired electricity generation. “The most difficult thing is finding cost assumptions for new technologies,” says Hernandez. “You can’t do this through a literature review, so we had many conversations with equipment manufacturers and plant operators.”

    The team considered two different forms of hydrogen fuel to replace natural gas, one produced through electrolyzer facilities that convert water and electricity into hydrogen, and another that reforms natural gas, yielding hydrogen and carbon waste that can be captured to reduce emissions. They also ran the numbers on retrofitting natural gas plants to burn hydrogen as opposed to building entirely new facilities. Their model includes identification of likely locations throughout the state and expenses involved in constructing these facilities.

    The researchers spent months compiling a giant dataset before setting out on the task of analysis. The results from their modeling were clear: “Hydrogen can be a more cost-effective alternative to lithium-ion batteries for peaking operations on a power grid,” says Hernandez. In addition, notes Gençer, “While certain technologies worked better in particular locations, we found that on average, reforming hydrogen rather than electrolytic hydrogen turned out to be the cheapest option for replacing peaker plants.”

    A tool for energy investors

    When he began this project, Gençer admits he “wasn’t hopeful” about hydrogen replacing natural gas in peaker plants. “It was kind of shocking to see in our different scenarios that there was a place for hydrogen.” That’s because the overall price tag for converting a fossil-fuel based plant to one based on hydrogen is very high, and such conversions likely won’t take place until more sectors of the economy embrace hydrogen, whether as a fuel for transportation or for varied manufacturing and industrial purposes.

    A nascent hydrogen production infrastructure does exist, mainly in the production of ammonia for fertilizer. But enormous investments will be necessary to expand this framework to meet grid-scale needs, driven by purposeful incentives. “With any of the climate solutions proposed today, we will need a carbon tax or carbon pricing; otherwise nobody will switch to new technologies,” says Gençer.

    The researchers believe studies like theirs could help key energy stakeholders make better-informed decisions. To that end, they have integrated their analysis into SESAME, a life cycle and techno-economic assessment tool for a range of energy systems that was developed by MIT researchers. Users can leverage this sophisticated modeling environment to compare costs of energy storage and emissions from different technologies, for instance, or to determine whether it is cost-efficient to replace a natural gas-powered plant with one powered by hydrogen.

    “As utilities, industry, and investors look to decarbonize and achieve zero-emissions targets, they have to weigh the costs of investing in low-carbon technologies today against the potential impacts of climate change moving forward,” says Hernandez, who is currently a senior associate in the energy practice at Charles River Associates. Hydrogen, he believes, will become increasingly cost-competitive as its production costs decline and markets expand.

    A study group member of MITEI’s soon-to-be published Future of Storage study, Gençer knows that hydrogen alone will not usher in a zero-carbon future. But, he says, “Our research shows we need to seriously consider hydrogen in the energy transition, start thinking about key areas where hydrogen should be used, and start making the massive investments necessary.”

    Funding for this research was provided by MITEI’s Low-Carbon Energy Centers and Future of Storage study. More

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    Energy storage from a chemistry perspective

    The transition toward a more sustainable, environmentally sound electrical grid has driven an upsurge in renewables like solar and wind. But something as simple as cloud cover can cause grid instability, and wind power is inherently unpredictable. This intermittent nature of renewables has invigorated the competitive landscape for energy storage companies looking to enhance power system flexibility while enabling the integration of renewables.

    “Impact is what drives PolyJoule more than anything else,” says CEO Eli Paster. “We see impact from a renewable integration standpoint, from a curtailment standpoint, and also from the standpoint of transitioning from a centralized to a decentralized model of energy-power delivery.”

    PolyJoule is a Billerica, Massachusetts-based startup that’s looking to reinvent energy storage from a chemistry perspective. Co-founders Ian Hunter of MIT’s Department of Mechanical Engineering and Tim Swager of the Department of Chemistry are longstanding MIT professors considered luminaries in their respective fields. Meanwhile, the core team is a small but highly skilled collection of chemists, manufacturing specialists, supply chain optimizers, and entrepreneurs, many of whom have called MIT home at one point or another.

    “The ideas that we work on in the lab, you’ll see turned into products three to four years from now, and they will still be innovative and well ahead of the curve when they get to market,” Paster says. “But the concepts come from the foresight of thinking five to 10 years in advance. That’s what we have in our back pocket, thanks to great minds like Ian and Tim.”

    PolyJoule takes a systems-level approach married to high-throughput, analytical electrochemistry that has allowed the company to pinpoint a chemical cell design based on 10,000 trials. The result is a battery that is low-cost, safe, and has a long lifetime. It’s capable of responding to base loads and peak loads in microseconds, allowing the same battery to participate in multiple power markets and deployment use cases.

    In the energy storage sphere, interesting technologies abound, but workable solutions are few and far between. But Paster says PolyJoule has managed to bridge the gap between the lab and the real world by taking industry concerns into account from the beginning. “We’ve taken a slightly contrarian view to all of the other energy storage companies that have come before us that have said, ‘If we build it, they will come.’ Instead, we’ve gone directly to the customer and asked, ‘If you could have a better battery storage platform, what would it look like?’”

    With commercial input feeding into the thought processes behind their technological and commercial deployment, PolyJoule says they’ve designed a battery that is less expensive to make, less expensive to operate, safer, and easier to deploy.

    Traditionally, lithium-ion batteries have been the go-to energy storage solution. But lithium has its drawbacks, including cost, safety issues, and detrimental effects on the environment. But PolyJoule isn’t interested in lithium — or metals of any kind, in fact. “We start with the periodic table of organic elements,” says Paster, “and from there, we derive what works at economies of scale, what is easy to converge and convert chemically.”

    Having an inherently safer chemistry allows PolyJoule to save on system integration costs, among other things. PolyJoule batteries don’t contain flammable solvents, which means no added expenses related to fire mitigation. Safer chemistry also means ease of storage, and PolyJoule batteries are currently undergoing global safety certification (UL approval) to be allowed indoors and on airplanes. Finally, with high power built into the chemistry, PolyJoule’s cells can be charged and discharged to extremes, without the need for heating or cooling systems.

    “From raw material to product delivery, we examine each step in the value chain with an eye towards reducing costs,” says Paster. It all starts with designing the chemistry around earth-abundant elements, which allows the small startup to compete with larger suppliers, even at smaller scales. Consider the fact that PolyJoule’s differentiating material cost is less than $1 per kilogram, whereas lithium carbonate sells for $20 per kilogram.

    On the manufacturing side, Paster explains that PolyJoule cuts costs by making their cells in old paper mills and warehouses, employing off-the-shelf equipment previously used for tissue paper or newspaper printing. “We use equipment that has been around for decades because we don’t want to create a cutting-edge technology that requires cutting-edge manufacturing,” he says. “We want to create a cutting-edge technology that can be deployed in industrialized nations and in other nations that can benefit the most from energy storage.”

    PolyJoule’s first customer is an industrial distributed energy consumer with baseline energy consumption that increases by a factor of 10 when the heavy machinery kicks on twice a day. In the early morning and late afternoon, it consumes about 50 kilowatts for 20 minutes to an hour, compared to a baseline rate of 5  kilowatts. It’s an application model that is translatable to a variety of industries. Think wastewater treatment, food processing, and server farms — anything with a fluctuation in power consumption over a 24-hour period.

    By the end of the year, PolyJoule will have delivered its first 10 kilowatt-hour system, exiting stealth mode and adding commercial viability to demonstrated technological superiority. “What we’re seeing, now is massive amounts of energy storage being added to renewables and grid-edge applications,” says Paster. “We anticipated that by 12-18 months, and now we’re ramping up to catch up with some of the bigger players.” More

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    Using aluminum and water to make clean hydrogen fuel — when and where it’s needed

    As the world works to move away from fossil fuels, many researchers are investigating whether clean hydrogen fuel can play an expanded role in sectors from transportation and industry to buildings and power generation. It could be used in fuel cell vehicles, heat-producing boilers, electricity-generating gas turbines, systems for storing renewable energy, and more.

    But while using hydrogen doesn’t generate carbon emissions, making it typically does. Today, almost all hydrogen is produced using fossil fuel-based processes that together generate more than 2 percent of all global greenhouse gas emissions. In addition, hydrogen is often produced in one location and consumed in another, which means its use also presents logistical challenges.

    A promising reaction

    Another option for producing hydrogen comes from a perhaps surprising source: reacting aluminum with water. Aluminum metal will readily react with water at room temperature to form aluminum hydroxide and hydrogen. That reaction doesn’t typically take place because a layer of aluminum oxide naturally coats the raw metal, preventing it from coming directly into contact with water.

    Using the aluminum-water reaction to generate hydrogen doesn’t produce any greenhouse gas emissions, and it promises to solve the transportation problem for any location with available water. Simply move the aluminum and then react it with water on-site. “Fundamentally, the aluminum becomes a mechanism for storing hydrogen — and a very effective one,” says Douglas P. Hart, professor of mechanical engineering at MIT. “Using aluminum as our source, we can ‘store’ hydrogen at a density that’s 10 times greater than if we just store it as a compressed gas.”

    Two problems have kept aluminum from being employed as a safe, economical source for hydrogen generation. The first problem is ensuring that the aluminum surface is clean and available to react with water. To that end, a practical system must include a means of first modifying the oxide layer and then keeping it from re-forming as the reaction proceeds.

    The second problem is that pure aluminum is energy-intensive to mine and produce, so any practical approach needs to use scrap aluminum from various sources. But scrap aluminum is not an easy starting material. It typically occurs in an alloyed form, meaning that it contains other elements that are added to change the properties or characteristics of the aluminum for different uses. For example, adding magnesium increases strength and corrosion-resistance, adding silicon lowers the melting point, and adding a little of both makes an alloy that’s moderately strong and corrosion-resistant.

    Despite considerable research on aluminum as a source of hydrogen, two key questions remain: What’s the best way to prevent the adherence of an oxide layer on the aluminum surface, and how do alloying elements in a piece of scrap aluminum affect the total amount of hydrogen generated and the rate at which it is generated?

    “If we’re going to use scrap aluminum for hydrogen generation in a practical application, we need to be able to better predict what hydrogen generation characteristics we’re going to observe from the aluminum-water reaction,” says Laureen Meroueh PhD ’20, who earned her doctorate in mechanical engineering.

    Since the fundamental steps in the reaction aren’t well understood, it’s been hard to predict the rate and volume at which hydrogen forms from scrap aluminum, which can contain varying types and concentrations of alloying elements. So Hart, Meroueh, and Thomas W. Eagar, a professor of materials engineering and engineering management in the MIT Department of Materials Science and Engineering, decided to examine — in a systematic fashion — the impacts of those alloying elements on the aluminum-water reaction and on a promising technique for preventing the formation of the interfering oxide layer.

    To prepare, they had experts at Novelis Inc. fabricate samples of pure aluminum and of specific aluminum alloys made of commercially pure aluminum combined with either 0.6 percent silicon (by weight), 1 percent magnesium, or both — compositions that are typical of scrap aluminum from a variety of sources. Using those samples, the MIT researchers performed a series of tests to explore different aspects of the aluminum-water reaction.

    Pre-treating the aluminum

    The first step was to demonstrate an effective means of penetrating the oxide layer that forms on aluminum in the air. Solid aluminum is made up of tiny grains that are packed together with occasional boundaries where they don’t line up perfectly. To maximize hydrogen production, researchers would need to prevent the formation of the oxide layer on all those interior grain surfaces.

    Research groups have already tried various ways of keeping the aluminum grains “activated” for reaction with water. Some have crushed scrap samples into particles so tiny that the oxide layer doesn’t adhere. But aluminum powders are dangerous, as they can react with humidity and explode. Another approach calls for grinding up scrap samples and adding liquid metals to prevent oxide deposition. But grinding is a costly and energy-intensive process.

    To Hart, Meroueh, and Eagar, the most promising approach — first introduced by Jonathan Slocum ScD ’18 while he was working in Hart’s research group — involved pre-treating the solid aluminum by painting liquid metals on top and allowing them to permeate through the grain boundaries.

    To determine the effectiveness of that approach, the researchers needed to confirm that the liquid metals would reach the internal grain surfaces, with and without alloying elements present. And they had to establish how long it would take for the liquid metal to coat all of the grains in pure aluminum and its alloys.

    They started by combining two metals — gallium and indium — in specific proportions to create a “eutectic” mixture; that is, a mixture that would remain in liquid form at room temperature. They coated their samples with the eutectic and allowed it to penetrate for time periods ranging from 48 to 96 hours. They then exposed the samples to water and monitored the hydrogen yield (the amount formed) and flow rate for 250 minutes. After 48 hours, they also took high-magnification scanning electron microscope (SEM) images so they could observe the boundaries between adjacent aluminum grains.

    Based on the hydrogen yield measurements and the SEM images, the MIT team concluded that the gallium-indium eutectic does naturally permeate and reach the interior grain surfaces. However, the rate and extent of penetration vary with the alloy. The permeation rate was the same in silicon-doped aluminum samples as in pure aluminum samples but slower in magnesium-doped samples.

    Perhaps most interesting were the results from samples doped with both silicon and magnesium — an aluminum alloy often found in recycling streams. Silicon and magnesium chemically bond to form magnesium silicide, which occurs as solid deposits on the internal grain surfaces. Meroueh hypothesized that when both silicon and magnesium are present in scrap aluminum, those deposits can act as barriers that impede the flow of the gallium-indium eutectic.

    The experiments and images confirmed her hypothesis: The solid deposits did act as barriers, and images of samples pre-treated for 48 hours showed that permeation wasn’t complete. Clearly, a lengthy pre-treatment period would be critical for maximizing the hydrogen yield from scraps of aluminum containing both silicon and magnesium.

    Meroueh cites several benefits to the process they used. “You don’t have to apply any energy for the gallium-indium eutectic to work its magic on aluminum and get rid of that oxide layer,” she says. “Once you’ve activated your aluminum, you can drop it in water, and it’ll generate hydrogen — no energy input required.” Even better, the eutectic doesn’t chemically react with the aluminum. “It just physically moves around in between the grains,” she says. “At the end of the process, I could recover all of the gallium and indium I put in and use it again” — a valuable feature as gallium and (especially) indium are costly and in relatively short supply.

    Impacts of alloying elements on hydrogen generation

    The researchers next investigated how the presence of alloying elements affects hydrogen generation. They tested samples that had been treated with the eutectic for 96 hours; by then, the hydrogen yield and flow rates had leveled off in all the samples.

    The presence of 0.6 percent silicon increased the hydrogen yield for a given weight of aluminum by 20 percent compared to pure aluminum — even though the silicon-containing sample had less aluminum than the pure aluminum sample. In contrast, the presence of 1 percent magnesium produced far less hydrogen, while adding both silicon and magnesium pushed the yield up, but not to the level of pure aluminum.

    The presence of silicon also greatly accelerated the reaction rate, producing a far higher peak in the flow rate but cutting short the duration of hydrogen output. The presence of magnesium produced a lower flow rate but allowed the hydrogen output to remain fairly steady over time. And once again, aluminum with both alloying elements produced a flow rate between that of magnesium-doped and pure aluminum.

    Those results provide practical guidance on how to adjust the hydrogen output to match the operating needs of a hydrogen-consuming device. If the starting material is commercially pure aluminum, adding small amounts of carefully selected alloying elements can tailor the hydrogen yield and flow rate. If the starting material is scrap aluminum, careful choice of the source can be key. For high, brief bursts of hydrogen, pieces of silicon-containing aluminum from an auto junkyard could work well. For lower but longer flows, magnesium-containing scraps from the frame of a demolished building might be better. For results somewhere in between, aluminum containing both silicon and magnesium should work well; such material is abundantly available from scrapped cars and motorcycles, yachts, bicycle frames, and even smartphone cases.

    It should also be possible to combine scraps of different aluminum alloys to tune the outcome, notes Meroueh. “If I have a sample of activated aluminum that contains just silicon and another sample that contains just magnesium, I can put them both into a container of water and let them react,” she says. “So I get the fast ramp-up in hydrogen production from the silicon and then the magnesium takes over and has that steady output.”

    Another opportunity for tuning: Reducing grain size

    Another practical way to affect hydrogen production could be to reduce the size of the aluminum grains — a change that should increase the total surface area available for reactions to occur.

    To investigate that approach, the researchers requested specially customized samples from their supplier. Using standard industrial procedures, the Novelis experts first fed each sample through two rollers, squeezing it from the top and bottom so that the internal grains were flattened. They then heated each sample until the long, flat grains had reorganized and shrunk to a targeted size.

    In a series of carefully designed experiments, the MIT team found that reducing the grain size increased the efficiency and decreased the duration of the reaction to varying degrees in the different samples. Again, the presence of particular alloying elements had a major effect on the outcome.

    Needed: A revised theory that explains observations

    Throughout their experiments, the researchers encountered some unexpected results. For example, standard corrosion theory predicts that pure aluminum will generate more hydrogen than silicon-doped aluminum will — the opposite of what they observed in their experiments.

    To shed light on the underlying chemical reactions, Hart, Meroueh, and Eagar investigated hydrogen “flux,” that is, the volume of hydrogen generated over time on each square centimeter of aluminum surface, including the interior grains. They examined three grain sizes for each of their four compositions and collected thousands of data points measuring hydrogen flux.

    Their results show that reducing grain size has significant effects. It increases the peak hydrogen flux from silicon-doped aluminum as much as 100 times and from the other three compositions by 10 times. With both pure aluminum and silicon-containing aluminum, reducing grain size also decreases the delay before the peak flux and increases the rate of decline afterward. With magnesium-containing aluminum, reducing the grain size brings about an increase in peak hydrogen flux and results in a slightly faster decline in the rate of hydrogen output. With both silicon and magnesium present, the hydrogen flux over time resembles that of magnesium-containing aluminum when the grain size is not manipulated. When the grain size is reduced, the hydrogen output characteristics begin to resemble behavior observed in silicon-containing aluminum. That outcome was unexpected because when silicon and magnesium are both present, they react to form magnesium silicide, resulting in a new type of aluminum alloy with its own properties.

    The researchers stress the benefits of developing a better fundamental understanding of the underlying chemical reactions involved. In addition to guiding the design of practical systems, it might help them find a replacement for the expensive indium in their pre-treatment mixture. Other work has shown that gallium will naturally permeate through the grain boundaries of aluminum. “At this point, we know that the indium in our eutectic is important, but we don’t really understand what it does, so we don’t know how to replace it,” says Hart.

    But already Hart, Meroueh, and Eagar have demonstrated two practical ways of tuning the hydrogen reaction rate: by adding certain elements to the aluminum and by manipulating the size of the interior aluminum grains. In combination, those approaches can deliver significant results. “If you go from magnesium-containing aluminum with the largest grain size to silicon-containing aluminum with the smallest grain size, you get a hydrogen reaction rate that differs by two orders of magnitude,” says Meroueh. “That’s huge if you’re trying to design a real system that would use this reaction.”

    This research was supported through the MIT Energy Initiative by ExxonMobil-MIT Energy Fellowships awarded to Laureen Meroueh PhD ’20 from 2018 to 2020.

    This article appears in the Spring 2021 issue of Energy Futures, the magazine of the MIT Energy Initiative.  More

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    Amy Watterson: Model engineer

    “I love that we are doing something that no one else is doing.”

    Amy Watterson is excited when she talks about SPARC, the pilot fusion plant being developed by MIT spinoff Commonwealth Fusion Systems (CSF). Since being hired as a mechanical engineer at the Plasma Science and Fusion Center (PSFC) two years ago, Watterson has found her skills stretching to accommodate the multiple needs of the project.

    Fusion, which fuels the sun and stars, has long been sought as a carbon-free energy source for the world. For decades researchers have pursued the “tokamak,” a doughnut-shaped vacuum chamber where hot plasma can be contained by magnetic fields and heated to the point where fusion occurs. Sustaining the fusion reactions long enough to draw energy from them has been a challenge.

    Watterson is intimately aware of this difficulty. Much of her life she has heard the quip, “Fusion is 50 years away and always will be.” The daughter of PSFC research scientist Catherine Fiore, who headed the PSFC’s Office of Environment, Safety and Health, and Reich Watterson, an optical engineer working at the center, she had watched her parents devote years to making fusion a reality. She determined before entering Rensselaer Polytechnic Institute that she could forgo any attempt to follow her parents into a field that might not produce results during her career.

    Working on SPARC has changed her mindset. Taking advantage of a novel high-temperature superconducting tape, SPARC’s magnets will be compact while generating magnetic fields stronger than would be possible from other mid-sized tokamaks, and producing more fusion power. It suggests a high-field device that produces net fusion gain is not 50 years away. SPARC is scheduled to be begin operation in 2025.

    An education in modeling

    Watterson’s current excitement, and focus, is due to an approaching milestone for SPARC: a test of the Toroidal Field Magnet Coil (TFMC), a scaled prototype for the HTS magnets that will surround SPARC’s toroidal vacuum chamber. Its design and manufacture have been shaped by computer models and simulations. As part of a large research team, Waterson has received an education in modeling over the past two years.

    Computer models move scientific experiments forward by allowing researchers to predict what will happen to an experiment — or its materials — if a parameter is changed. Modeling a component of the TFMC, for example, researchers can test how it is affected by varying amounts of current, different temperatures or different materials. With this information they can make choices that will improve the success of the experiment.

    In preparation for the magnet testing, Watterson has modeled aspects of the cryogenic system that will circulate helium gas around the TFMC to keep it cold enough to remain superconducting. Taking into consideration the amount of cooling entering the system, the flow rate of the helium, the resistance created by valves and transfer lines and other parameters, she can model how much helium flow will be necessary to guarantee the magnet stays cold enough. Adjusting a parameter can make the difference between a magnet remaining superconducting and becoming overheated or even damaged.

    Watterson and her teammates have also modeled pressures and stress on the inside of the TFMC. Pumping helium through the coil to cool it down will add 20 atmospheres of pressure, which could create a degree of flex in elements of the magnet that are welded down. Modeling can help determine how much pressure a weld can sustain.

    “How thick does a weld need to be, and where should you put the weld so that it doesn’t break — that’s something you don’t want to leave until you’re finally assembling it,” says Watterson.

    Modeling the behavior of helium is particularly challenging because its properties change significantly as the pressure and temperature change.

    “A few degrees or a little pressure will affect the fluid’s viscosity, density, thermal conductivity, and heat capacity,” says Watterson. “The flow has different pressures and temperatures at different places in the cryogenic loop. You end up with a set of equations that are very dependent on each other, which makes it a challenge to solve.”

    Role model

    Watterson notes that her modeling depends on the contributions of colleagues at the PSFC, and praises the collaborative spirit among researchers and engineers, a community that now feels like family. Her teammates have been her mentors. “I’ve learned so much more on the job in two years than I did in four years at school,” she says.

    She realizes that having her mother as a role model in her own family has always made it easier for her to imagine becoming a scientist or engineer. Tracing her early passion for engineering to a middle school Lego robotics tournament, her eyes widen as she talks about the need for more female engineers, and the importance of encouraging girls to believe they are equal to the challenge.

    “I want to be a role model and tell them ‘I’m a successful engineer, you can be too.’ Something I run into a lot is that little girls will say, ‘I can’t be an engineer, I’m not cut out for that.’ And I say, ‘Well that’s not true. Let me show you. If you can make this Lego robot, then you can be an engineer.’ And it turns out they usually can.”

    Then, as if making an adjustment to one of her computer models, she continues.

    “Actually, they always can.” More

  • in

    Manipulating magnets in the quest for fusion

    “You get the high field, you get the performance.”

    Senior Research Scientist Brian LaBombard is summarizing what might be considered a guiding philosophy behind designing and engineering fusion devices at MIT’s Plasma Science and Fusion Center (PSFC). Beginning in 1972 with the Alcator A tokamak, through Alcator C (1978) and Alcator C-Mod (1991), the PSFC has used magnets with high fields to confine the hot plasma in compact, high-performance tokamaks. Joining what was then the Plasma Fusion Center as a graduate student in 1978, just as Alcator A was finishing its run, LaBombard is one of the few who has worked with each iteration of the high-field concept. Now he has turned his attention to the PSFC’s latest fusion venture, a fusion energy project called SPARC.

    Designed in collaboration with MIT spinoff Commonwealth Fusion Systems (CFS), SPARC employs novel high temperature superconducting (HTS) magnets at high-field to achieve fusion that will produce net energy gain. Some of these magnets will wrap toroidally around the tokamak’s doughnut-shaped vacuum chamber, confining fusion reactions and preventing damage to the walls of the device.

    The PSFC has spent three years researching, developing, and manufacturing a scaled version of these toroidal field (TF) coils — the toroidal field model coil, or TFMC. Before the TF coils can be built for SPARC, LaBombard and his team need to test the model coil under the conditions that it will experience in this tokamak.

    HTS magnets need to be cooled in order to remain superconducting, and to be protected from the heat generated by current. For testing, the TFMC will be enclosed in a cryostat, cooled to the low temperatures needed for eventual tokamak operation, and charged with current to produce magnetic field. How the magnet responds as the current is provided to the coil will determine if the technology is in hand to construct the 18 TF coils for SPARC.

    A history of achievement

    That LaBombard is part of the PSFC’s next fusion project is not unusual; that he is involved in designing, engineering, and testing the magnets is. Until 2018, when he led the R&D research team for one of the magnet designs being considered for SPARC, LaBombard’s 30-plus years of celebrated research had focused on other areas of the fusion question.

    As a graduate student, he gained early acclaim for the research he reported in his PhD thesis. Working on Alcator C, he made groundbreaking discoveries about the plasma physics in the “boundary” region of the tokamak, between the edge of the fusing core and the wall of the machine. With typical modesty, LaBombard credits some of his success to the fact that the topic was not well-studied, and that Alcator C provided measurements not possible on other machines.

    “People knew about the boundary, but nobody was really studying it in detail. On Alcator C, there were interesting phenomena, such as marfes [multifaceted asymmetric radiation from the edge], being detected for the first time. This pushed me to make boundary layer measurements in great detail that no one had ever seen before. It was all new territory, so I made a big splash.”

    That splash established him as a leading researcher in the field of boundary plasmas. After a two-year turn at the University of California at Los Angeles working on a plasma-wall test facility called PISCES, LaBombard, who grew up in New England, was happy to return to MIT to join the PSFC’s new Alcator C-Mod project.

    Over the next 28 years of C-Mod’s construction phase and operation, LaBombard continued to make groundbreaking contributions to understanding tokamak edge and divertor plasmas, and to design internal components that can survive the harsh conditions and provide plasma control — including C-Mod’s vertical target plate divertor and a unique divertor cryopump system. That experience led him to conceive of the “X-point target divertor” for handling extreme fusion power exhaust and to propose a national Advanced Divertor tokamak eXperiment (ADX) to test such ideas.

    All along, LaBombard’s true passion was in creating revolutionary diagnostics to unfold boundary layer physics and in guiding graduate students to do the same: an Omegatron, to measure impurity concentrations directly in the boundary plasma, resolved by charge-to-mass ratio; fast-scanning Langmuir-Mach probes to measure plasma flows; a Shoelace Antenna to provide insight into plasma fluctuations at the edge; the invention of a Mirror Langmuir Probe for the real-time measurements of plasma turbulence at high bandwidth.

    Switching sides

    His expertise established, he could have continued this focus on the edge of the plasma through collaborations with other laboratories and at the PSFC. Instead, he finds himself on the other side of the vacuum chamber, immersed in magnet design and technology. Challenged with finding an effective HTS magnet design for SPARC, he and his team were able to propose a winning strategy, one that seemed most likely to achieve the compact high field and high performance that PSFC tokamaks have been known for.

    LaBombard is stimulated by his new direction and excited about the upcoming test of the TFMC. His new role takes advantage of his physics background in electricity and magnetism. It also supports his passion for designing and building things, which he honed as high school apprentice to his machinist father and explored professionally building systems for Alcator C-Mod.

    “I view my principal role is to make sure the TF coil works electrically, the way it’s supposed to,” he says. “So it produces the magnetic field without damaging the coil.”

    A successful test would validate the understanding of how the new magnet technology works, and will prepare the team to build magnets for SPARC.

    Among those overseeing the hours of TFMC testing will be graduate students, current and former, reminding LaBombard of his own student days working on Alcator C, and of his years supervising students on Alcator C-Mod.

    “Those students were directly involved with Alcator C-Mod. They would jump in, make things happen — and as a team. This team spirit really enabled everyone to excel.

    “And looking to when SPARC was taking shape, you could see that across the board, from the new folks to the younger folks, they really got engaged by the spirit of Alcator — by recognition of the plasma performance that can be made possible by high magnetic fields.”

    He laughs as he looks to the past and to the future.

    “And they are taking it to SPARC.” More