It's my pleasure today to introduce our speaker, that's Professor Zach Hartwig. I think a lot of you know Zach, but maybe not everybody, so I thought I'd provide a little bit of background. Zach got his PhD from MIT, the Nuclear Science and Engineering Program department, where he did some very interesting work that is quite different than what he's working on now. He built and tested a very novel and interesting new diagnostic for interrogating the first wall in a tokamak. It used an energetic ion beam steered by the magnets in the tokamak to hit different places on the wall, and determine the characteristics of the first wall.
Deposits, erosion, and such. And it had the advantage that it was in situ, and so he could make measurements between runs, or even between shots. Now, up until that point, the only kind of measurements available were ex situ, where we would take, first of all, material out of the tokamak between campaigns, where you got basically one measurement per year. And the conditions you were looking at were averaged over an entire year's of experiments. So big improvement there. After graduation, he worked as a postdoc for a while, and then accepted an appointment to the NSE faculty.
Zach was part of the original SPARC Skunk Works, back when it wasn't a multibillion dollar company, but just a few people kicking around ideas. And then was one of the cofounders of CFS itself. And once the project really got rolling, he led the R&D team, which worked on high temperature superconductor cables and magnets.
And that all led to the successful test of a toroidal field model coil just a few months ago in the fall of '21. So today he's going to talk about those efforts, and some of the results. Zach? Terrific. Thanks for the introduction, Martin.
I'm sort of reminded, this is our second go round at IAP. We did this about five years ago now. So OK, welcome everybody.
We have a pretty ambitious agenda for today, so I'm going to try to get through it on time. What we're going to talk about today is what I call the long road to 20 tesla on the SPARC toroidal field model coil. And it's really a magnet origin story. It's to provide a little bit of the maybe sort of excitement and color behind the magnet project, to help us better put the magnet in context. So you can see the magnet, you can see the test facility that we built at MIT to test it here on the screen. We're going to dive into that in more detail.
So I want to acknowledge all the people listed here at the bottom who provided material for this talk. Sort of an enormous outpouring of information. So I want to start in the place I think which is most important to doing big projects, and that's to acknowledge the people who make projects happen. That's really something that I came to learn firsthand over the four or five years of leading projects here, is that people make projects.
So I want to thank the exceptional, exceptional team from Commonwealth Fusion Systems and from MIT. You can see a number of their faces here in the test hall, who delivered on the TFMC project through some pretty extraordinary circumstances, as you can tell by everybody wearing face masks for about 15 months of this project. So I tried to list everybody here who had an important hand in this project. I'm sure I missed a few people. I don't have time to go through everybody, I do want to acknowledge a few people.
Rui Vieira, the chief engineer. And then the engineering group leaders, Brian LaBombard, Chris Lammi, Joy Dunn, Ted Golfinopoulos, and Phil Michael. A number of other people, just terrific effort.
Also want to acknowledge our vendors, who delivered under some pretty extraordinary circumstances, again, through a couple of tough years for them. So a great group of people, many of whom are going to be involved in a lot of the things you hear about today. So I want to also just acknowledge that the TFMC project, and the success that we'll talk about, is a pretty nice confirmation of a hypothesis that we put forth about five or six years ago, which was the idea that we could develop a new model for collaborative research where we would combine the best of academia with new companies, with a startup. So we could actually start a company like CFS, grow it alongside of the R&D that was going on, to the point that it would be capable of taking the research out of MIT and commercializing it. And so, this partnership of CFS and PSFC that was proposed some years ago really came to fruition in this project.
So really, a nice thing to recognize. So let's talk about the SPARC toroidal field model coil project, which I'll refer to is TFMC in most of this talk. And for the purposes here, I'll sort of characterize it as doing four things. The first was really to develop the basic conductor technologies that we needed to build magnets. You can see a picture of two of them that we developed on the left, cables and coils.
And then taking those technologies, we had to design and build the model coil itself. You can see a picture of that here, being rigged by a team at MIT. We had to then, in parallel, build and commission a test facility to actually go off and characterize the magnet. And then we had to actually run the test. So we wanted, in our first test, to get to 20 tesla.
It's about 15 to 20 times more powerful than a hospital MRI, which is sort of the magnets some of us might be familiar with in everyday life. And we wanted to achieve 20 tesla in our first test, and we did that. So this project, which was pretty ambitious, was completed in four years or so by MIT and CFS in partnership with our vendors. And when I had a chance to sort of think about giving this talk, I wanted to step back a little bit, and sort of think, that was a pretty impressive run that we had over a pretty difficult period of time.
And so it sort of begs the question, how does this project compare to other things that may have been done in a similar vein? And I list one here. This is called the ITER central solenoid model coil. So it's another type of magnet that was built as an experiment. You can see a picture of it here. How does this compare to what we did over the last few years? So in terms of the project scope, it was roughly the same as TFMC.
The idea of building a large coil, representative scale, testing it, et cetera. The coil itself, as you can see here, is quite a bit larger due to the technology that they had at the time. A little bit more stored energy. But it's about the same electrical current, and it's actually almost half-- a little more than half of the magnetic field, which makes some of the challenges easier. It took about a decade to develop this project.
We might say two years to develop the conductor technology, eight years to design, fabricate, and test the coil. And perhaps most striking in contrast, if you look at the participants, I list some of them here. This was a dozen plus major industries across three continents.
You'll see names like Lockheed Martin, Mitsubishi Heavy Industry, and Saldo, a large Italian contractor. So there's a lot of work around the world, with the test site in Japan. And so when I kind of had a chance to reflect on our own accomplishments here, it sort of raised a question, which was, while our coil is much smaller, we, along with our vendors, executed a similar project scope in less than half of the time, including 15 months with COVID 19 restrictions, with almost everything-- with an exception of large scale machining and forging and some component fabrication-- really done in house here.
And like the CSMC project that you see here, it worked on the first time out of the gate. And it begs the question, how? So that's what we want to talk about in part for this talk today. So what I want to do, we'll lay out the agenda here. It's a little ambitious, as I said. I want to try to go beyond asking the what question-- what is TFMC-- and I want to try to get to the how and why. So I want to go a little level deeper.
Maybe deeper than we typically tend to go in technical talks. So I want to ask some questions, like, how did we get to the TFMC, and through it? Why was this magnet project successful, and on such a challenging schedule? And why did this project happen? Why did it come out of MIT, and done here with MIT and our partner, CFS? Why did it happen here, and not somewhere else? So in order to do all that, what I want to do is convince you of three things in this talk. So I want to convince you first that high field superconducting magnets enable a better path to fusion energy. That's why we're doing them.
I want to make a sort of hypothesis that we can test in this talk, which is that there are sort of three key attributes that go some ways to answering this how and why question. And I list them here, we'll talk about them in a second. And then after we look at how it was possible and why it happened here, then I want to convince you that high field superconducting magnet technology is approaching maturity with the test's successful build and test of the model coil.
So to do this, here's our agenda. We're going to look very briefly at magnets, and magnetic fields, and fusion energy. We don't have too much time. Then what I'd like to do is trace what I have sort of come to appreciate as the 100 year odyssey of high field magnet R&D at MIT that led us right up to the TFMC, and enabled us to execute the project in part. And then we'll get an overview of the TFMC project, and what its success might mean for fusion.
So first, I want to take a look at these three terms which are going to underline, sort of sit in the background of a lot of what we're going to talk about in the middle of the talk. And it's the three things that I think are really important to look at when we review this history and try to ask the questions how did we do this, why was it at MIT, why was it successful? The first thing I think is important is culture. Culture of an organization and the project. And so you can kind of define that as the pattern of behavior ingrained in an organization that defines how it solves problems.
It includes beliefs, norms, values, mindsets that shape our actions. Culture is a very intangible thing, it's very difficult to communicate, especially in a talk. And so you'll see a lot of it implicitly, I hope, in what we talk about and what we see.
But I thought-- when I was discussing with Joe Minervini, former head of PFCC Magnet Division, about this talk, he gave me a great quote, which I think puts you-- gives you a sense of what that culture is at MIT. And what he said was, in keeping with MIT tradition, we tackle only the most difficult technical challenge in the field of magnets. Always pushing, always developing first of kind new technologies. The second thing I want to talk about and try to examine here is something I've come to call institutional capabilities.
And here, I would say this is the intrinsic ability to move quickly and confidently, and at scale. So this includes things like equipment, processes, systems, working knowledge that's in place to get something done. And we'll see that.
And the third is, I sort of said when I introduced the team and thanked everybody, it's really about the people. So I would just define that as integrated experience, expertise, and the efforts of those people who bring all of their selves, and put that into the project. And so we're going to try to see elements of all three of these things. Before we begin in earnest, I do want to just issue an apology in advance.
I can't possibly show everything that people sent me upon my request. It was an enormous deluge of material, which is terrific. We're going to try to cover a lot of material, and inaccuracies and emissions are inevitable. And I do want to point out, this is just one perspective to look at this project and what came before. And it's a bit of a historical one at that. So we're going to spend a little more time looking at the history, rather than that some of the innovations in the TFMC, to take a bit of a 10,000 foot view.
And I do want to make a point here that I'm going to say MIT-- that's often going to refer to a number of different laboratories and centers that now operate as one as the Plasma Science and Fusion Center. So I list them here. Francis Bitter Magnet Laboratory, National Magnet Laboratory, Plasma Science and Fusion Center, and all the work that was done before those centers came about. So with that, let's take a brief look at why we're interested in superconducting high field magnets for fusion. And so we'll do this as a series of primer lessons, if you like. So three lessons which I'll state and just quickly go through.
The first is that we're interested in superconductors because we can make magnetic fields with very, very small power requirements. And you can see an example of that here. So this is the Alcator C-Mod copper toroidal field magnet. So this is a magnet we operated here at MIT for about 25 years. You can get a sense of its scale. It's a copper magnet.
It's not superconducting. It produces magnetic fields of about 12 tesla. The challenge is it only runs for about four seconds until it heats up, because it's a resistive magnet and can melt. And in order to power it, it takes about 225 megawatts for four seconds. That's about the size of a small power plant in a city.
And you can see some of the enormous infrastructure, rooms of equipment that are required to power that magnet that we had to operate and maintain at MIT. In contrast, the TFMC superconducting magnet is about the same scale. You look at the picture. It has a field that's about two times as high, which is good.
We can operate it continuously for as long as we like, and it only takes about 120 kilowatts, give or take. So that's about 2,000 times less power just to operate that magnet. And if we were to put these magnets in a fusion power plant, that significant savings in energy to run the magnet, we can actually sell as electricity onto the grid. So that's a good thing for a fusion power plant. The other point to make is that modern superconductors not only allow us to do all this great stuff with low power, but we can achieve much higher magnetic fields, and in much smaller sized devices than we can otherwise. And I'll take an example from the world of cyclotrons.
So this is a picture on the right of 184 inch cyclotron that Ernest Lawrence built at Berkeley in the mid 1940s. It's a copper magnet cyclotron, and you can get a sense of the scale that's involved in this piece of equipment. So it made a beam of hundred MeV protons, it had a magnetic field of about two tesla. It had to weigh about 5,000 tons to do what it needed to do, because, in large part, of the magnetic field. At the bottom right, you can see where better superconductors take us.
Niobium 3 tin, in this case, for people who are interested. This is a modern cyclotron for cancer therapies that was designed and prototyped here at MIT. Has about the same beam characteristics, but it's a much higher magnetic field at nine tesla. And it's only 50 tons, so it's about 100 times less mass.
Which, depending on your scaling, that tends to mean about 100 times cheaper to build. So the same is true of fusion, when we can make something 100 times smaller, it's effectively 100 times cheaper, faster, easier to build. So that's a good thing. So that's why we like superconductors. The second primer lesson here is to make the point that fusion always maximizes the magnetic field that it can get out of magnet technologies that exist at the time.
And that's simply because the performance of fusion gets better like magnetic field to the fourth. B to the fourth. And so you can see in this sort of graphical timeline, starting in the '50s and '60s we had copper wire.
So you can see Lyman Spitzer here with the first stellarator at Princeton. Very low magnetic field. Then we took a step, a big step, in fact, up in magnetic field with something called cryogenic Bitter plate magnets. We'll talk about those in a minute. We were able to get very, very high field, but again, at the expense of very high power consumption.
So then, what we did was, we knew we had to take a hit in field to get into the superconducting range of magnets, which we wanted for a fusion power plant. So while we went down in field in the next generation of fusion devices with niobium titanium magnets, and then niobium 3 tin devices. We did get superconducting magnets, which are appropriate for fusion. Now what's happened in about the last 10 years is, a new superconductor called rare earth barium copper oxide-- not going to go into too much detail about what it is, but it is essentially a transformational change in capabilities of superconductor.
It is much, much better than anything that's happened before, from a magnetic field perspective and an engineering perspective. Has a lot of advantages. And so it's pretty clear from this timeline that at some point, somebody is going to build a fusion machine out of the next greatest superconductor, because it lets us go to much higher field, we get much higher performance in our fusion machine. And that leads us to the last lesson in this primer, which is that high field magnets open a very attractive and accelerated path to fusion energy. And this is a path that was first really put forth by MIT maybe five or six years ago, and is now being walked by MIT and CFS. But it's also inspired quite a lot of others around the world to see that this is an attractive path.
Where we were in about 2016 was finishing the operation of Alcator C mod, our high field tokamak here, where we proved out that high field fusion science was a really viable and attractive option. We knew that if we could build high field magnets that got us 12 tesla, 13 tesla, 14 tesla magnetic fields in the center of the plasma of a tokamak, we could build very small devices that could put out hundreds of megawatts of fusion power, and ultimately electricity, very efficiently. But the superconducting concepts we had at the time, high field superconductors, were kind of only at the drawing board or benchtop scale.
There was really a gap between what was needed and what was available. And that's basically what the toroidal field model coil project was. It was an idea to take what was sort of on the drawing board-- we'll talk about that-- do some of the developments necessary to build the electrical conductors to make the magnets, and then demonstrate that the magnets at a representative scale were really ready to go.
So with that sort of quick tour of superconductors in high field in mind, I'd like to turn to this idea of history, and how 100 years of thinking about high field magnets at MIT was able to lead us to the TFMC, and ultimately enable it. And so, it's often been said that stories have a beginning, and stories have an end. And I often find in technical talks, we tend to focus a lot on the end of the story.
The latest and greatest, the newest inventions, the things that we did that enabled it to go. And we'll talk about those things, but what I also want to do here is sort of focus on the beginning and the middle of the story, and look at the enormous foundation that had to be in place for us to take those next steps and actually deliver on the toroidal field model coil project. So our story begins perhaps in an unlikely place, which is in 1923 in a basement in New York City. And the story begins, as these stories often do, in academia, with a young person desperately seeking to find a PhD project that would pass muster. This person, of course, is Francis Bitter. As many of you know, he was born in 1900, he had a career that only a physicist in the early part of the 20th century could have.
We'll talk about that in a second, but what he's doing in 1920 is wondering what he's going to do for a PhD. And there's a great quote from his autobiography that says, "as I was walking around the corridors of Columbia, my eye lit on an impressive looking magnet in an empty laboratory." And so, it's always dicey to pinpoint the moment where a chain of events starts, but this might be the moment for our story here.
And so what Bitter does is, he goes on to use that magnet, he completes his PhD, he measures the magnetic moment of noble gases. But he's greatly disappointed. And he's disappointed because the magnet technology at the time does not allow him to go much above two to three tesla. It's an iron based magnet that saturates, and so no matter what you do to it, you'll never get the higher fields that Bitter needed to do the atomic and nuclear physics that he was interested in. So he goes on from here to have a pretty stunning career, like I said, you could only have in the early 20th century.
He goes to Germany in the 1920s, he spends time with Planck, with Schrodinger, he makes friends with Leo Szilard of nuclear weapons fame. He takes the subway home with Einstein, and discusses the lectures at the time. He comes back from Germany to complete his PhD. He goes off to California, works for Robert Millikan, a Nobel Prize winning American physicist, and Hale, the astronomer. But all of the time he's doing this, in the back of his mind, he's thinking, this problem of magnets needs to be solved. And so, as he's thinking about what to do for a career, he has this quote, which I pulled from his book.
He says, "one project that appealed to me was to make a stronger magnetic field that could be made with the iron based magnets. The problem was to discover how far it was practical to go." And so that last part about how far it was practical to go really provides the map and the vision that we're very much still walking on today. So what happens? So Bitter comes to MIT in the 1930s, and he starts to come up with concepts for how to build the first high field magnet.
And he hits on one, which we'll see, but he has a problem. And the problem is, as we've seen, that copper magnets take an enormous amount of power to run because they're resistive, and MIT simply doesn't have the capabilities. So luckily, Bitter is at MIT, and he calls up Vannevar Bush, who's a titan of an early and mid 20th century science and technology. Vannevar Bush picks up the phone and pulls a few strings at Con Edison, the local power company in Boston, and he hooks Bitter up with a spot in the basement of the Scotia Street substation. And Bitter is able to have enough power to test his magnet. Now I was sort of curious-- because this happened in Boston, I was kind of curious to see if this place still exists, and it turns out it does.
And so you could go one and a half miles across the Charles River into Boston, and you can find a very much turn of the 20th century brick building right here on Scotia Street. And it's in the basement of that building where the first high field magnet is ever tested. And I think it's by no accident that, 80 years later, the TFMC is tested just a mile and a half away.
But it really puts a pin down in the map, and says that high field magnet technology is going to be developed at MIT. So ultimately, what Bitter does is he invents something called the Bitter plate magnet, and the idea here is to provide magnetic fields above 3 tesla for science and engineering. So you can see magnet number one, and then magnet number three, which was a more advanced design.
And then ultimately, here on the right, you can see a modern Bitter plate magnet. Now the way these work is pretty ingenious, but very simple. So in terms of generating field, what he does is he stacks copper plates between insulators, and he forces the current to take many turns as it spirals around, which generates an axial magnetic field with no iron. But the real problem that turns out Bitter had to solve was how to remove all the heat from these magnets. And so he puts the magnets in a pressure vessel, essentially.
He force flows water around those magnets, but more importantly, through the series of grooves that are in these plates. And that enables very high flux cooling of the copper, which is very hot. So in terms of what ultimately this legacy does for TFMC, we have very high field, it can be done. The fundamentals of high field magnets are in place, and we know how to remove heat from magnets. Very nice.
Well, it turns out there's sort of an extraordinary comparison that we can make between Bitter's first high field magnet and the toroidal field model coil, despite the fact they're separated by almost 85 years. If you look at the sketch of magnet number one, what you'll see is Bitter put several plates into a spiral configuration that generates the magnetic field on axis. He puts that inside a pressure vessel, and he force flows coolant around and through the plates of this magnet. If we look at the toroidal field model coil that we built here in the last two years, it is exactly the same type of magnet. We have a number of plates that carry current in a spiral fashion, we put those plates together to make a stronger magnetic field.
And then we put that stack of plates into a pressure vessel, a case, and we force flow cooling around the magnet and through special channels that we put into those pancakes. So in 1935, Bitter had essentially foreseen the key elements of magnets, and one that we would use 85 years later, which is how to arrange the plates, and how to keep them cold. Really, an extraordinary visual comparison here.
So the next step in our journey is when a professor by the name of Bruno Coppi comes to MIT. And Bruno Coppi realizes that we could take Bitter plate magnets, we could bend them-- not to produce an axial field, but to produce a toroidal field-- and we could confine a plasma within those magnets. And so that leads to a series of devices known as the Alcator devices, here at MIT. So Alcator A, which had fields of around 12 tesla on coil, Alcator C, 17 tesla, and Alcator C-Mod, 12 tesla field on coil. All of these tokamaks used Bitter plate magnet technology.
And so there's a lot of learning that was done here at the PSFC because of this. So we learned not only about copper magnets, we learned about high field structural supports, how to forge with vendors and machine large scale support systems, how to take good care of vacuum, and other things. And that experience translated directly to the TFMC. So for example, and we had to do our own forgings and machining in this case, you see a forging of a very large structural case and pressure vessel being done at our vendors. Ken Stevens of the TFMC team there in the background.
We had the in house experience, the metallurgical experts to call on, who could work directly with us on that process. The Alcator C mod did a number of other things in the Alcator program. It left a whole lot of infrastructure around, and a knowledge about how to use that infrastructure. So this is an example. This is a picture from May of 2018. This was the first time we carried out a soldering process on anything that mattered early in the program.
And we actually used the oven that was used to build the C-Mod TF coils. So it was really the expertise and in the infrastructure that came from Alcator allowed us to do very quick, at scale R&D for TFMC. Another aspect I wanted to touch on for Alcator was just simply the idea about large scale integration and operations of complex systems. So a number of people from MIT involved, and you can see some examples of what that looks like here. So the idea that we have experienced design engineers and modelers who understand the interfaces, and how to put together enormously complex systems. Other things like the installation and the operation of the 225 MVA alternator.
You can sort of see this was an alternator delivered by rail to MIT from Con Edison in Brooklyn. Sort of occurred to me putting this together, Con Edison may have done more for fusion and high field magnets than any other power company. But they did donate this, which enabled us to power the Alcator C mod magnets.
And then of course, for 25 years, we had to assemble, maintain, and operate a world class fusion facility. And these experiences were just enormously helpful to training a world class team of students, scientists, engineers, technicians, et cetera. And this was really driven home to me when I was at the Magnet Technology Conference and Steve Gourlay, who's the former head of the US Magnet Development Program, gave a lessons learned talk. Sort of his key lessons from a lifetime of building big magnets.
And one of the things he said which struck me was that critical steps in high field superconducting magnets dictate the need for high quality, experienced technicians. And so many of our technicians on the C-Mod program, for example, or on the TFMC program, came up through the Alcator A, Alcator C, Alcator C mod and had a lifetime of experiences that made the TFMC possible. So a really nice touch point with others in the field. And so I think, in terms of the impact for TFMC, that is really a legacy, and it's that Alcator C-Mod sort of gave us this culture of close to expert cooperation between students, scientists, engineers, technicians, on a complex... OK, now I want to turn to a different magnet technology, and this was the development of the first ever superconducting cables for fusion magnets. So this was led by a guy named Bruce Montgomery, Mitch Hoenig, Mike Steeves, other people at the PSFC starting in the '70s.
And so you can see a picture of what these things look like. This is basically a way to bundle many, many smaller superconductors together, such that you can carry the 50 to 100 kiloamps necessary for fusion magnets, but keep them cold, and have enough structure to support them. This idea came up in the mid '70s.
Joe Minervini told me Bruce Montgomery took this to the World Fusion Program in the '70s, and was largely laughed out of the room that this was never a practical way to do it. And of course, the last laugh was Bruce's, ultimately, because now CIC technology underlines every single fusion superconducting fusion magnet, with a few exceptions, that have ever been built in the world. So this was really a big foundation for the next step in fusion technology. And so the things we learned here were things like how to design and fabricate superconducting conductors, how to do high flux cryogenic cooling, and all the infrastructure that was left behind at MIT to do this type of work. And so, again, to make a touch point with TFMC, when we started the program in 2017, we just happened to have a whole bunch of heavy equipment lying around that would let us build full scale, jacketed superconducting cables. And so you can see a picture-- this is Rui Vieira and Pete Stahl, people who knew how to work with this equipment and had experience that resulted in very quick R&D that was quite successful in developing a new type of cable.
And a group of people and techniques that allowed us to wind those things into coils. So really, this effort, another platform that TFMC could stand on. Those cables were then used by many around the world, but also by people at MIT. One example is the project we looked at earlier.
So this is the ITER central solenoid model coil. MIT was responsible for building half of this coil, and then supervising the integration of that coil into the test facility. This occurred in the late '90s to the early 2000s, it involved a lot of people from the PSFC who then went on to participate in TFMC. So you can see some examples of things that we did. So MIT established a fabrication facility down in Hingham.
You can see a lot of big tents, you can see small people here to give you a sense of the scale of what had to be done in a very clean facility. So there are a lot of large scale and complex activities that the engineers and technicians had to work out. And then of course, the model coil module that built had to be integrated into the larger test facility. So MIT had people on site to do that.
So the real lessons that were developed here for TFMC were establishing fabrication facilities, designing and building complex magnets, and integrating those things with test facilities. And so I really like this picture, because it's not an accident that the CSMC model coil on the left-- 20 years ago-- and the TFMC on the right look so similar, and that they worked on the first attempt. So it was really our participation, and the people that came before me in the CSMC, who enabled the experience and the expertise to put these magnets together, but also to seamlessly integrate them into what are inevitably very complex test facilities. So really, a direct-- really a direct connection of what we did then with what we did on TFMC. So I want to-- oh, no.
My slides got a little messed up here, unfortunately, so I'll carry you through this, even though there's something in the way. So the next step that I want to follow was the development of a new type of superconducting cable. So the CIC cable we just looked at was an older style of superconductor. Now we want to carry this forward to develop REBCO cables.
And so the idea here, which was led by Makoto Takayasu at MIT, was to take many, many small, flat tapes, and to combine them together in such a way that they could carry the very large currents to be cooled, and to do other things that we needed for fusion. And so Makoto really deserves an enormous amount of credit, because while a lot of us here at MIT were doing plasma physics and looking at other things, Makoto was actually developing the first conductors out of this new type of superconductor that were suitable for fusion. Unfortunately, all those pictures are hidden behind-- hidden behind this slide. Makoto did things like joints, he developed cables, he developed-- you can see here on the right-- some of the first coils, and proved that they could work at very high conditions without any degradation. And so there was a lot of takeaways for TFMC. The basic technology, how to build these style of REBCO cables, what the joints might look like, how to bend them, et cetera.
And of course, I think it's important to point out that Makoto's work has now made impacts all around the world. So there are many types of this conductor technology which are being developed, and they're all based on this T stack concept that came out of MIT. For TFMC, it was really good that we had that T stack work being done for the last 10 or 15 years, because it enabled something that was necessary to test the coil. And so you can see here on the top left, these are superconducting REBCO cables that we developed, similar to Makoto's cables, and using a lot of his learning. We called them viper cables. This was a technology we were able to move on very quickly, and so we developed these in the first years of the project.
These are now sort of the foundation for some of the other magnets that are being developed for SPARC, but they also provided what we call a cold bus, which is essentially a way to get 50 kiloamps of current from this component in the test hall, called the current leads, all the way over to the magnet, which is sitting here on the right in this picture. So you have to have a way to get current from one place to another. And in this case, there were really no alternatives out there, and so it was really nice that we had developed this technology. You can see a picture of what those cold bus cables look like here, and sort of a picture of them being installed.
All comes from the T stack concept. So I realize once again, I managed to fudge my slides, and I put a slide on top of another, which is very unfortunate. So it goes. So what I want to talk about next is another concept that came out of MIT, this case from Yuki Iwasa's group in the Francis Bitter Magnet Laboratory. And this was the idea that REBCO coils could be built with no insulation, no electrical insulation. And this was a pretty radical idea at the time.
This was a completely new way to build a magnet, and to operate it, to achieve high field. So these were ideas that were developed by people like Suyong Han, Dongkeun Park, who's pictured here behind this magnet-- sorry Dongkeun-- Yuki Iwasa, Juan Bascunan, and others. And they basically built the first coils in late 2009 and 2010, and ran them through a number of tests. And they sort of proved out the fundamental physics and engineering of these coils. And these coils had a number of advantages.
So for example, they could carry a lot of current in a small space. That means the magnet could be very compact, but it could be very high field. They did a lot of the early physics of how a no insulation coil would work, how electrical currents would move around in these magnets. They also did something which I think is important.
You can kind of still see it here, it's a little obscured. Is they sort of reignite this race to high magnetic field. So you can see year here on the x-axis. Tesla is here on the x-- y axis, excuse me. And you see a number of coils that MIT built were really the first in a series of other groups starting to take this technology and push the limits up to where it stands now, to Suyong Han's coil in Korea, which is an all REBCO NI coil of about 46 tesla. And so I wanted to make the same point as I did for Makoto, that Yuki, and Dongkeun and Suyong's work here at MIT has now had impact far beyond MIT.
So we have groups at CERN, National High Field Lab, doing really innovative things with NI coils. And other groups in fusion-- Tokamak Energy in England, Seoul National University where Suyong Han now is developing this NI technology with a look towards fusion magnets, very similar to what we're doing here. And so for TFMC, again, this was an amazing foundation for us, because that first coil that was developed in 2009, about six years later, the seeds of what would become the TFMC team came along and wound our own single tape REBCO coil, with some assistance from Yuki's group. So we were sort of just getting our feet wet and learning how to do some of these things.
And that led directly then, in 2018, for us to make a number of changes and innovations to this technology, to make the magnets suitable for fusion-- large scale fusion magnets. So it was really helpful. So when you see a picture of Bill Beck and Brian LaBombard wound the first NINT coil. And when we were looking at the first post soldered NINT coil, we did so with an idea there was a lot of confidence and understanding of how these coils went that really helped us make the innovations necessary for our own magnetic designs. So as we're coming into the more modern era, I want to end with two things.
The first is not necessarily a project, it's actually an academic course. So this is a classic graduate class that's taught by Dennis Whyte. In this case, it was taught in the spring of 2010. A number of us participated in this course that went on to have key roles in SPARC and the TFMC.
But what this class resulted in was a paper that published the first proposed design of a toroidal field magnet coil with REBCO. And you can see some pictures of the magnets, it's a cross-section of the magnets here. And while I can say-- looking back, there's a lot, of let's say, well intentioned naivete in it, this was really the first time a group had sat down, I think, and thought really seriously what a modern REBCO coil would look like.
And so that was really a benefit. So the benefit for us on TFMC was that we knew what high field fusion could do in terms of device-- of fusion device performance, size, cost. We had a good working knowledge of what some of the challenges might be with building REBCO toroidal field magnets, and what REBCO was and how to think about it.
And maybe importantly, a group of highly enthusiastic, dare I say zealous, students who, in 2010, were really eager to see this brought to the world. And I pulled a quote out from the paper, which I think is relevant, from the conclusion, which says, "unlike LTS, the previous generation of superconductors, REBCO makes it conceivable to build a reactor with a magnetic field on the order of 20 tesla to exploit the magnetic field to the fourth dependence of fusion power in a DT burning tokamak reactor." So that is SPARC, essentially.
And its ARC, and its the other types of high field fusion devices that are being proposed. And you can find a lot of it there. I do want to make a sort of funny anecdote, which is, if you look at this plot on the right, this is sort of a system study that was done by myself and Bob Mumgaard, and a few others.
And what it did was it-- you sort of throw a whole bunch of things-- cost, and operations, and everything else, into this magnet design, and tried to pick what the optimum operating temperature was for this new generation of magnets. And nobody had really thought, I think, in great detail perhaps about exactly what temperature might be the right one for a fusion magnet. And it turns out, you can see the black line, there's a nice sweet spot, sort of between 10 and 20k.
And we all sort of joke amongst ourselves, every other fusion magnet that's been proposed with this always says 20 kelvin, 20 kelvin. And it would be sort of amusing if this was the nexus of where that idea-- where the genesis of where this idea came from. A bunch of students sort of putting things together for a course.
The last thing I want to mention, again, not a project or class, but an organization. And it goes to the institutional capabilities that MIT were able to tap into, and that's a lab at MIT Bates. So the Bates Research and Engineering Center formerly operated a large linear accelerator up in Middleton, Massachusetts. And so in some ways, I sort of think of Bates as our sister lab at MIT, a lab working on large scale, complex technology projects.
And so some people-- and I list them here-- came onto the TFMC team in 2019 to augment our capabilities very quickly. And so that translated into a really, I think, advantageous situation for TFMC, because a lot of things could be done very quickly. And so when we look at, for instance, the TFMC Test Hall, which we'll go into more detail in a second, we see a lot of things that come from all of the experience at Bates in operating-- building and operating very large scale equipment. So to give just two examples, a power supply that powered a detector that was doing some nuclear physics. We had the experience and the vendor connections to very quickly turn that into a 50 kilowatt power supply.
Similarly, for a large detector that was built and operated at Bates, we could import high power electric bus cables and, boom, drop them into the TFMC to allow us to go quickly. So that huge base of knowledge that we can tap into, and the people who came along with it that were really helpful, and really helped augment our ability to go as quickly as we wanted to do on TFMC. So I want to end our high field odyssey here, and it occurred to me as I was putting this talk together, my grandmother used to tell me I was always somebody who tried to put 10 pounds of shit in a five pound bag, and that's clearly what I'm trying to do here by going through the history of high field fusion magnets at MIT. There's so much that we didn't cover, and people sent me a lot of details about, that is in that 100 year history, and I just want to mention some of those things. Everything from test facilities, to metallurgical alloy development, high yield cyclotrons, Moda generators, maglev trains.
There's just a lot of projects and experience that were done here that deserve time that we just don't have to give them. An example, just to point it out, levitate a dipole experiment was a project here where we had a two ton superconducting coil. It was levitated in the middle of a vacuum chamber with other magnets to confine a plasma. Very advanced, sort of a bold approach to doing plasma confinement.
And a fun fact, turns out one of the magnets that was there was the first ever high temperature superconductor magnet anywhere in the fusion industry. So that came out of MIT. Another one, which is one of my favorites that I hadn't come across before, was the so called baby magnet, which was built by Bruce Montgomery, Makoto Takayasu, and others at MIT.
And the idea here was actually assist in treatment for babies to help them connect esophagus when it was not properly grown in the womb. So this is a particular type of treatment where, using little magnetic bullets and a magnetic field, you could actually help surgeons elongate the esophagus and make a surgical connection. So I think that is maybe by far the most unique magnet I've seen come out of PSFC, and certainly again testifies to the confidence that we have at MIT in building pretty novel magnets.
So now we sort of enter the last part of our talk. We've been going for about 45 minutes, and we have about 10 minutes to go, and then I'll wrap up. So I want to talk about now, the TFMC project, with all of that history and knowledge behind us of what went into it.
So let's talk about the TFMC. So we had a lot to do on the TFMC. We looked at the four components of what the project would be. Doing the conductor development, building the coil, building the test facility, and running the test. All that was really done with the idea of retiring the risk in the production and operation of large scale, steady state REBCO magnets. So there's a number of things we had to do.
We knew this magnet technology needed to be done, such that it could go immediately into SPARC, into a high field tokamak. And that really constrained and set the tone for what we had to do. So as an example, we had to design it properly. It had to achieve the same requirements that it would see in SPARC, or close. We had to develop the EM modeling tools to design the SPARC magnets. In terms of supply chain, we knew we had to grow the REBCO manufacturers to provide us with enough material.
We had to develop structural materials, get large scale vendors to participate with us. In terms of fabrication, we wanted two link manufacturing processes, process control scalability, as a fundamental part of TFMC. We would have to tackle the challenges of high field operation. So structural loading, stress and strain on the superconductors that can damage them. And it wasn't, as I say, just about building a coil.
We actually had to develop a whole bunch of novel things that enabled us to test this coil successfully on a very tight timeline. And ultimately, we had to deal with something called quench. So that's the idea that magnets have a lot of stored energy. Superconducting magnets, when they're cold, life is good. But if something goes wrong, all that energy can go into heating the coils up, which can lead to damage.
There are other aspects, like having high pressure coolant induced Eddy forces that create challenges that had to be dealt with. So this is sort of the glamour shot of the TFMC. So it is the largest REBCO magnet ever built, typically, depending on how you look at it, by an order of magnitude or a few. So you can see an example of the size of the magnet.
It's about three meters by two meters. It's D shaped, both to allow high concentration of the magnetic field in the corners to get up to that 20 tesla margin. But it's also D shaped to help us prove out sort of the magnetic field topology, the fabrication techniques with a D shaped magnet, amongst other things. So remember back to the Bitter plates? We had 16 plates, or pancakes, that we stack into the core of the magnet.
We'll look at that in a second. So that magnet has about 270 kilometers of superconductor in it. That's enough to go from here to Albany in one continuous stretch. We operate this magnet at about 20 kelvin, again, maybe because a bunch of students 12 years ago thought that was a good idea.
We used supercritical helium at very high pressure, so about 20 bar. You know, 300 and say, 50 PSI. The current is about 40 kiloamps, we get in excess of 20 tesla on axis, and the magnet itself weighs about 10 kilograms, or about 11 imperial tons. So it's a pretty impressive magnet. Very much a step change by about a factor of 1,000, in terms of mass of the largest REBCO magnet that's ever been built.
So a little more detail as to how do we build this. So you can think of this as really a REBCO stacking plate, no insulation magnet. Kind of putting together a lot of the REBCO stack work and the NI work that came earlier from MIT. So what we do is we take a steel plate, and we machine grooves in it on one side, where we put stacks of REBCO cables. On the other side, we have grooves for cooling.
Those REBCO stacks terminate at the so called internal pancake to pancake joints such that when we stack multiple pancakes, the current has a path to go around in a spiral to generate the magnetic field, and then into the next pancake where it can continue to spiral. And then we've developed a VPI-- vacuum pressure impregnation solder process to bond everything mechanically, electrically, and thermally together. So then what do we do? We take all these pancakes, we stack them up into a winding pack, which you can see here. So you can think of that as the core of the magnet. We put two plates, top and bottom, with these parts you see here called current leads. You can think of those essentially the plus and minus terminals of a battery, or something that uses power.
So that's where we hook up our current and inject it into the magnet, so that it can create field. And then just like the Bitter plate concept you saw earlier, we can take this magnet, put it in a large structural case to deal with the electric mechanical forces. But it also serves as a pressure vessel where we can force flow cooling through all the channels in the magnet to make sure that those superconducting pancakes stay cold. So why do we want to do it this way? What are the real advantages of the magnet? There's a number of proposed design features, and the goal of the TFMC project and other magnet projects will be to prove these design features out.
So the first is it's modular, simple construction compared to other generations of magnets. Rapid assembly, easy maintenance. You can swap pancakes in and out. It's very scalable for commercial production. This is intrinsically a low voltage technology.
That was one of the early advantages that was proven about NI magnets. So it's less than a volt. That's very different than other fusion superconducting magnets, which have to operate at 5 or 10 kilovolts, where you can get arcs, you can get lightning bolts, and cause-- or just cause damage or destroy your magnets. And that's really nice for us. It means minimal insulation, simple fabrication, low voltage systems around the magnet, and increased safety for people.
The magnet has high thermal stability. That means it's very hard for it to stop being superconducting. It's robust to damage or defects that are caused by manufacturing, and off normal events in operation are recoverable. It sits in the bottom of a nice well, and it likes to be cold.
The other idea was this pressure vessel cooling approach. While this is standard for Bitter plate magnets, it's very different than the traditional superconducting magnets that exist today. This gives us enhanced heat removal, the ability to optimize locally where we want to cool. Very simple manifolding to get the supercritical helium in it out. The magnet has very high current in a small space. That gives us a compact magnet, and it lets us take some of the space that would be needed with other technologies, and put it to other uses.
And then, another proposal is that this magnet, like the smaller NI magnets that have been built, are essentially passively safe to a quench event, meaning that if the magnet were to quench and warm up, the magnet would be just fine. It doesn't require a whole bunch of infrastructure to actually protect it. So all of these are sort of proposals to be proven out in the TFMC project, and in others.
So that's the magnet. What about the test facility? So the test facility was built at MIT in about 18 months. You see a pretty impressive time lapse here, where we took the cell that was outside of Alcator-- so this is about a 10,000 square foot hall. It was filled to the brim with equipment. We basically cleaned that out over the span of nine months, and then nine months later, had built, assembled, and commissioned the test facility that we needed for the TFMC, but also for other future magnet projects. So a very, very quick turnaround, showing what the team achieved in a short time.
Now it's a very unique and capable test facility. So just to point out a few things that you see in this picture, we have a 50 kiloamp power supply over here, we have a 50 kiloamp warm bus that brings our current down to this large vacuum vessel here. Inside, we have something called the current leads, whose job it is is to take this very large electrical current from room temperature at the top, down to cryogenic temperatures, in this case 20 kelvin at the bottom.
And then a series of cables to bring that current into the toroidal field model coil, which sits in this large vacuum vessel here. So we have all the support systems that we need. A cryo system that's liquid free, we have a large crane, we have a whole bunch of other systems you see here at the bottom that are required to operate what is really a full scale and complex test facility. Now of all the innovations we had to do to make the magnet test possible, I just want-- I have time, and I want to focus on one, which is what we call the 50 kiloamp binary REBCO current leads and feeder system. So this is essentially another major innovation where, I think these are the largest current leads of their kind by a factor of two to three that have ever been built. And so these were largely designed, assembled, and commissioned in house, because there were simply no other alternatives out there that could be developed and delivered on the schedule that we needed.
And the idea being, the current comes in at the top, it comes down to a 77K stage, and then is brought down to 20 kelvin. So it's cooled by liquid nitrogen in the middle, and supercritical helium at the bottom. And then the idea being that that series of Viper cable that we saw before can carry that current-- on the positive terminal, can carry that current through a series of cables into the magnet-- which is down here on the right-- and then return at the negative terminal back to the power supply. So these were sort of an entire project in and of themselves, and they were tested quite successfully to 41 kiloamps before the test, with all joints meeting our specification by a factor of a few. So a really nice series of innovations. So I want to wrap up here with the first test.
The job here was to assess the steady state operation at full performance of the coil, and we really asked three questions. Does the peak field on coil exceed 20 tesla? That was a key metric for us. Does the magnetic field and the power dissipation-- the heating within this magnet-- match these very detailed models that a team of people developed to predict the behavior of current and heat and field in this new type of no insulation magnet, where those things were not as well known before we did the test? You can see a picture of what the field distribution looks like from one of the models, where we have very high fields in the corner.
And in fact, if you look at these black rectangles, these are the winding pack. This is where the actual superconductor is in the magnet. You can see over a large portion of the coil, we get fields in excess of 20 tesla. Very high electromechanical forces right here, which was one of the design objectives. And so this winding pack had an array of extensive instrumentation to measure just about everything we wanted to see.
And of course, our modeling team and the physicists worked with the operations team to develop a test program. This is a prediction of that program, where over the span of about four days, we ramp up the coil in steps to get to our peak performance objective. And so I'm very happy to report, as many of you probably know already, and saw in articles, but this test in late August, early September was very successful. It largely went according to the plan.
So you can see here, we ramped up the current over the span of about 60 hours, pausing in steps to look at the physics of the magnet, and tracking the magnetic field that we got. You can see a significant fraction exceeded 20 tesla on the magnet. And so that was mission achieved for the whole team. A big moment of relief, and then the magnet was ramped down. I'm not going to go into all the details. I leave them here for people who want to go over them, but I think the point to be made here that a number of things were achieved in the test.
This high field 20 tesla performance in a large scale magnet was confirmed, we had very low resistance interpancake joints, which is-- joints are always a big risk to a superconducting coil. If they're not made properly, the coil heats up and doesn't work. We had very good cryogenic performance, the ability to control and maintain temperatures in the magnet.
The significant structural loading on the magnet, in some cases, almost approaching a gigapascal was handled as designed by the winding pack, that big structural case. And we had very good match to the simulated predictions of how this coil would operate in steady state. So a lot of nice science and engineering objectives were achieved. So I want to close here, and just sort of make the point that while we've kind of been looking at a lot of individual projects, sort of gate posts along the journey, if you like, I think the graphic on the left illustrates for me one of the points I wanted to make here, was not the individual gate posts but really this long line that connects what we were able to do on the TFMC, all the way back to Frances Bitter in 1935. It really is a continuity of things that happened here that enabled the success. And I think, for me, it was a really interesting oppor
2022-03-25