Plasma
Rogerio Jorge receives first grant as a professor
Congrats to Prof. Rogerio Jorge who was awarded his first grant as a professor! The three-year, $500,000 National Science Foundation grant, titled “Moment Approach to Multiscale Plasmas,” will be used to fund a graduate student and postdoc on the project.
“Astrophysical plasmas appear in more than 90% of the universe — for example, on the surface of the sun or in the intergalactic medium — and there’s still a lot of things that we don’t understand about them,” Jorge says. “We need to study phenomena in astrophysical plasmas and try to replicate them numerically to better understand them.”
Jorge’s work will focus on the so-called collisionless regime of these plasmas, where particles travel for a long time before experiencing any collision. He says this regime is difficult to model, both experimentally and numerically.
“We’ve proposed a new method that has two parts. The first one is to try to simplify the equations using a reduced model, called a moment model,” Jorge says. “Second, it’s using machine learning to reduce it even more.”
Jorge and his team have the moment model theory ready to be applied. For the machine learning step, they will use JAX, an open-source machine learning framework developed by the DeepMind team at Google that many physicists are starting to use in their research.
Jorge plans to investigate one intriguing phenomenon in collisionless plasmas: how the acceleration of super-thermal particles occurs versus thermodynamic heating. This will help scientists understand how charged particles in a plasma become energized, a phenomenon applicable to both laboratory and astrophysical plasmas. He will also apply this new approach to the problem of magnetic reconnection in collisionless plasmas, a problem he says is difficult to model due to the topology changes that occur in short time scales.
“We need new models to try to handle these complex scenarios without spending months and months on a single simulation,” Jorge says.
NSF grants require investigators to address the broader impacts of their research, defined as “the potential to benefit society and contribute to the achievement of specific, desired societal outcomes.” Jorge plans to work with the department’s Wonders of Physics outreach program to create realistic movies that simulate these astrophysical plasma environments. For example, he hopes to show, in detail, what is happening with magnetic reconnection in auroras or around the surface of the sun, with both using the new code developed through his research.
For this research, Jorge is collaborating with experimentalists at UW-Madison’s WiPPL facilities, and computational plasma physicists at UCLA, MIT, and Princeton.
Madison Symmetric Torus operates stable plasma at ten times the Greenwald Limit
If net-positive fusion energy is to ever be achieved, density is key: the more atomic nuclei crashing into each other the more efficient the reaction will be. Nearly 40 years ago, Martin Greenwald identified a density limit above which tokamak plasmas become unstable, and the so-called Greenwald limit has at best been exceeded by a factor of two in the ensuing decades.
In a new study published July 29 in Physical Review Letters, physicists at the University of Wisconsin–Madison produced a tokamak plasma that is stable at 10 times the Greenwald limit. The findings may have implications for tokamak fusion reactors, though the researchers caution that their plasma is not directly comparable to that in a fusion reactor.
“Tokamak devices are considered a leading contender in the race to build a nuclear fusion reactor that generates power in the same way as the sun,” says Noah Hurst, a scientist with the Wisconsin Plasma Physics Laboratory (WiPPL) and lead author on the study. “Our discovery of this unusual ability to operate far above the Greenwald limit is important for boosting fusion power production and preventing machine damage.”
Tokamaks are toroidal devices, basically hollow metal donuts that churn ionized plasma through the tube by applying both a magnetic field and an electrical current. This shape has been shown to be particularly adept at confining the plasma, which is required to reach the high temperature and density needed for fusion. But the design can also lead to instabilities in the plasma: as its density increases, the plasma becomes more turbulent, causing the plasma to give up all its energy to the wall and cool off.
The device that the WiPPL team used in this new study is the Madison Symmetric Torus, or MST. For many years, MST has operated as one of the leading programs studying the reversed field pinch, a toroidal configuration closely related to the tokamak. MST was designed to anticipate operation as a tokamak, allowing direct comparison of the two toroidal configurations in the same device. Unlike other tokamaks, the metal donut that houses the MST plasmas is thick and highly conducting, allowing for more stable operation..
In 2018, MST scientists received National Science Foundation funding to build power supplies that are programmable, facilitating easier access to a range of toroidal plasma configurations, from tokamak to reversed field pinch. Hurst was hired in 2019 to study MST plasmas in tokamak mode with the new power supply.
“My job was to try to find ways to make the plasma go unstable,” Hurst says. “I tried, and I found that, well, in many cases, it doesn’t. It was surprising.”
![a graph with time [ms] on the x axis and electron density) aka plasma density on the y axis. Several data lines, given in a rainbow of colors, all go up within the first few ms, hold steady for up to 40ms, and then drop down to 0. A dotted line, representing the Greenwald limit, is shown around 0.75 on the y axis; all but one of the data lines goes well above that dotted line, up to 10x the value of the Greenwald limit](https://www.physics.wisc.edu/wp-content/uploads/2024/07/nlim_summary.png)
The Greenwald limit is just the ratio of the plasma density to the product of the plasma current and plasma size, a simple metric that allows comparison of different devices and operating conditions. Since the limit was defined, only a handful of devices have operated above it, and by at most a factor of two.
“Here, we were at a factor of ten,” Hurst says. “Future reactor-scale tokamaks will likely need to operate near or above the Greenwald limit, so if we can better understand what’s causing the density limit and understand the physics of how we got to ten times the limit, then maybe we have a shot at doing something about it.”
Though the researchers feel confident in their results, they are unexpected. The team is actively exploring explanations.
“The first thing we would ask is, what’s different about our machine relative to other machines?” Hurst says. “MST is very different because it was designed with a thicker wall than most tokamaks. Also, most tokamaks produce lower-resistance plasmas, so they don’t need these large voltages like we did in order to run.”
Hurst also emphasizes that these results are unlikely to be directly applicable to fusion reactors, such as ITER and others that are being built in the hopes of being the first net-positive energy production tokamaks. But he and the team are cautiously optimistic.
“Our results were obtained in a low magnetic field, low temperature plasma, which is not capable of fusion power production. Still, we were the first ones to be able to do this, and you have to start somewhere,” Hurst says. “We’re going to keep studying these plasmas, and we think that what we learn might help higher-performance fusion devices to operate at the higher densities they need to be successful.”
This study was supported by the U.S. Department of Energy (DE-SC0020245); by the Wisconsin Plasma Physics Laboratory, a research facility supported by the U.S. DOE Office of Fusion Energy Sciences under contract DE-SC0018266; and by a National Science Foundation Major Research Instrumentation grant (PHY 1828159).
First plasma marks major milestone in UW–Madison fusion energy research
A fusion device at the University of Wisconsin–Madison generated plasma for the first time Monday, opening a door to making the highly anticipated, carbon-free energy source a reality.
Over the past four years, a team of UW–Madison physicists and engineers has been constructing and testing the fusion energy device, known as WHAM (Wisconsin HTS Axisymmetric Mirror) in UW’s Physical Sciences Lab in Stoughton. It transitioned to operations mode this week, marking a major milestone for the yearslong research project that’s received support from the U.S. Department of Energy.
“The outlook for decarbonizing our energy sector is just much higher with fusion than anything else,” says Cary Forest, a UW–Madison physics professor who has helped lead the development of WHAM. “First plasma is a crucial first step for us in that direction.”
WHAM started in 2020 as a partnership between UW–Madison, MIT and the company Commonwealth Fusion Systems. Now, WHAM will operate as a public-private partnership between UW–Madison and spinoff company Realta Fusion Inc., positioning it as major force for fusion research advances at the university.
Cristian Vega awarded Callen Award for Excellence in Theoretical Plasma Physics Research
Congrats to (now) Dr. Cristian Vega who won the Callen Award for Excellence in Theoretical Plasma Physics Research! Vega won the award on April 29, just days before defending his thesis on May 3.
The Callen Award is awarded annually to a UW–Madison plasma physics graduate student for achievements in plasma theory. Now-retired Professor Emeritus Jim Callen was a long-time faculty member in the Nuclear Engineering and Engineering Physics department. Callen was also an affiliate faculty member of the Physics department.
Welcome, Professor Vladimir Zhdankin!
Theoretical plasma astrophysicist Vladimir Zhdankin ‘11, PhD ’15, returns to UW–Madison as an assistant professor of physics on January 1, 2024. As a student, Zhdankin worked with Prof. Stas Boldyrev on solar wind turbulence and basic magnetohydrodynamic turbulence, which are relevant for near-Earth types of space plasmas. After graduating, Zhdankin began studying plasma astrophysics of more extreme environments. He first completed a postdoc at CU-Boulder, then a NASA Einstein Fellowship at Princeton University. He joins the department from the Flatiron Institute in New York, where he is currently a Flatiron Research Fellow.
Please give an overview of your research.
These days, most of my interest is in the field of plasma astrophysics — the application of plasma physics to astrophysical problems. Much of the matter in the universe is in a plasma state, such as stars, the matter around black holes, and the interstellar medium in the galaxy. I’m interested in understanding the plasma processes in those types of systems. My focus is particularly on really high energy systems, like plasmas around black holes or neutron stars, which are dense objects where you could get extreme plasmas where relativistic effects are important. The particles are traveling at very close to the speed of light, and there’s natural particle acceleration occurring in these systems. They also radiate intensely, you could see them from halfway across the universe. There’s a need to know the basic plasma physics in these conditions if you want to interpret observations of those systems. A lot of my work involves doing plasma simulations of turbulence in these extreme parameter regimes.
What are one or two research projects you’ll focus on the most first?
One of them is on making reduced models of plasmas by using non-equilibrium statistical mechanical ideas. Statistical mechanics is one of the core subjects of physics, but it doesn’t really seem to apply to plasmas very often. This is because a lot of plasmas are in this regime that’s called collisionless plasma, where they are knocked out of thermal equilibrium, and then they always exist in a non-thermal state. That’s not what standard statistical mechanics is applicable to. This is one of the problems that I’m studying, whether there is some theoretical framework to study these non-equilibrium plasmas, to understand basic things like: what does it mean for entropy to be produced in these types of plasmas? The important application of this work is to explain how are particles accelerated to really high energies in plasmas. The particle acceleration process is important for explaining cosmic rays which are bombarding the Earth, and then also explaining the highest energy radiation which we see from those systems.
Another thing I’m thinking about these days is plasmas near black holes. In the center of the Milky Way, for example, there’s a supermassive black hole called Sagittarius A*, which was recently imaged a year or two ago by the Event Horizon Telescope. It’s a very famous picture. What you see is the shape of the black hole and then all the plasma in the vicinity, which is in the accretion disk. I’m trying to understand the properties of that turbulent plasma and how to model the type of radiation coming out of the system. And then also whether we should expect neutrinos to be coming out, because you would need to get very high energy protons in order to produce neutrinos. And it’s still an open question of whether or not that happens in these systems.
What attracted you to UW–Madison?
It’s just a perfect match in many ways. It really feels like a place where I’m confident that I could succeed and accomplish my goals, be an effective mentor, and build a successful group. It has all the resources I need, it has the community I need as a plasma physicist to interact with. I think it has a lot to offer to me and likewise, I have a lot to offer to the department there. I’m also really looking forward to the farmers’ market and cheese and things like that. You know, just the culture there.
What is your favorite element and/or elementary particle?
I like the muon. It is just a heavy version of the electron, I don’t remember, something like 100 times more massive or so. It’s funny that such particles exist and this is like the simplest example of one of those fundamental particles which we aren’t really familiar with, it’s just…out there. You could imagine situations where you just replace electron with a muon and then you get slightly different physics out of it.
What hobbies and interests do you have?
They change all the time. But some things I’ve always done: I like running, skiing, bouldering indoors, disk golf, racquet sports, and hiking. (Cross country or downhill skiing?) It’s honestly hard to choose which one I prefer more. In Wisconsin, definitely cross country. If I’m in real mountains, the Alps or the Rockies, then downhill is just an amazing experience.
Welcome, Professor Rogerio Jorge!
Plasma theorist Rogerio Jorge will join the UW–Madison physics department as an assistant professor on January 1, 2024. He joins us from IST in Lisbon, Portugal, where he is a research professor. Jorge completed his first postdoc at the University of Maryland at College Park, then accepted a Humboldt Fellowship where he worked on the design of fusion energy devices in Greifswald, Germany.
Please give an overview of your research.
My work is twofold: I uncover basic plasma physics phenomena and apply my plasma physics knowledge to the realization of fusion energy. My most recent work is devoted to the design of Stellarators, a type of fusion machine that is free of major instabilities and disruptions. Here, we try to have this clean renewable energy available to the world as fast as possible. While I’ve been doing research on fusion since my PhD studies, where I focused on one type of device called the Tokamak, when I went to the U.S. for my postdoc, I started focusing on the Stellarator. The Stellarator has had a lot of research since the ’60s, but only recently it had a big resurgence.
Thanks to the enormous progress in computational power, I do a lot of simulations for my work. I have worked on several codes, each focusing on a particular physics or engineering problem such as electromagnetic coils, stability, turbulence, and energy retention, which are all used in combination to do designs for new machines. I also collaborate with startups seeking to rapidly develop fusion energy and supervise students and postdocs who are trying to get new designs for new machines. Most of our work is in the realm of classical physics, based on things that people learn while they’re majoring in physics such as electrodynamics and electromagnetism. But then, we couple it with new computational and mathematical techniques, such as machine learning, to streamline our workflow.
We have ideas for Stellarator design that could allow for much better performance than we had before so that the resulting devices achieve higher temperatures and higher densities. However, we should always take into account that theory and experiment may operate on different planes. We are in contact with experimentalists who sometimes tell us, “Your machine is too complicated to build!” And then we have to go back and incorporate their constraints into the design.
Once you arrive in Madison, what are one or two research projects you think your group will focus on first?
Stellarator design and optimization will be one of the main branches, and we have many projects that either could be started or have started in my research group now that we will be continuing in Madison. One of these topics is the confinement of fast particles resulting from fusion reactions, that is, alpha particle dynamics. These must stay confined long enough to continuously feed energy to the plasma, leading to what we call a burning plasma. Right now, the machines we have, they’re still prototypes, meaning that they haven’t made many studies on the physics of burning plasmas. We still need to do a lot of research on it. Once we turn on the machine and start getting a lot of energy, we must be able to predict what’s going on. Burning plasma physics or fast particle physics is one of the major issues. Besides burning plasma physics, I will also continue the work on stellarator optimization, with a particular focus on how machine learning can help us obtain increasingly better designs and how to incorporate experimental constraints into the optimization. Another branch will be the study of basic plasma physics with a particular focus on astrophysical plasmas. During my PhD, I developed a method to accurately incorporate collisions between charged particles in plasmas. I intend to further develop that technique, creating a numerical tool that is easy to use and can be used to predict extreme events in space, as well as predict the behavior of plasmas in the lab, such as the Wisconsin Plasma Physics Laboratory.
What attracted you to Madison?
Madison has one of the best physics departments in the world, particularly in my area of plasma physics. I believe it’s one of the top places that people think of when they do the sort of work that I do, stellarators and basic plasma physics. This is because there is here a prototype fusion device, a myriad of experimental plasma physics facilities, and people doing state-of-the-art theory and simulation. Furthermore, when I visited Madison, I loved the views, the lakes, and the overall quality of life.
What is your favorite element or elementary particle?
I think I like the neutrino. It was fun learning about neutrinos in particle physics. They were thought to have no mass, but their flavors can actually oscillate while they travel, and this yields a very tiny but finite amount of mass. Besides, they can go through essentially everything without getting detected, they’re basically invisible! It’s something that you think you know what it is, and you know all the calculations and you understand it, but at the end of the day experiments and the nature tells you that you don’t exactly know what you think you know. There’s more to the story there and they seem so simple, yet there is more to the story.
What hobbies and interests do you have?
Definitely music. I play the guitar and I like to learn how to play new instruments. I have a few instruments around the house but the one that I am learning how to play right now is the violin. Like the neutrino, even with only four strings, it’s a deceivingly complicated instrument.
Stas Boldyrev earns DOE funding to investigate turbulence in relativistic plasmas
This post was adapted from a U.S. Department of Energy announcement
The U.S. Department of Energy (DOE) announced August 23 that it is funding $9.96M to support research in basic plasma science and engineering as well as frontier plasma science experiments at several midscale DOE Collaborative Research Facilities (CRFs) across the nation. The funding will go to 20 universities — including to UW–Madison physics professor Stas Boldyrev — four private companies, and one national laboratory.
The funding will cover 30 awards aimed at supporting basic plasma science research as well as increasing research productivity and participation of U.S. researchers in the CRFs. The awards include three-year single investigator or small group projects as well as short-term, one-time seed funding projects.
“Basic and low temperature plasma science is an important area with many scientific and technological impacts,” said Jean Paul Allain, DOE Associate Director of Science for Fusion Energy Sciences. “The research funded under this FOA will enable the U.S research community to address many fundamental and technological science challenges helping to ensure continued American leadership in this critical field.”
Boldyrev’s award will investigate turbulence in relativistic plasmas, which is more poorly understood compared to its non-relativistic counterpart. Relativistic plasma turbulence exists in extremely hot and energetic natural systems, where plasma and/or particle flow rates approach the speed of light, and it is required to explain radiation spectra of space phenomena such as solar flares or galactic nuclei jets.
“This project intends to develop analytical, phenomenological, and numerical models of turbulent energy cascades, and describe how such turbulence interacts with magnetic fields,” Boldyrev says. “We will concentrate on universal statistical properties of relativistic turbulence, which makes the results applicable to various lab, space, and astronomy environments, where such turbulence is present.”
Vadim Roytershteyn of the Space Science Institute is a co-investigator.
Ke Fang, Ellen Zweibel earn Simons Foundation funding to study electrodynamics in extreme environments
Much of what we understand about fundamental physics is based on experiments done in the convenient “lab” of earth. But our planet is just one location, with its own relatively mild electromagnetic field. Do forces and energies work the same on earth as they do in all corners of the universe?
“It’s never guaranteed, as we see many theories break down at extreme environments,” says University of Wisconsin–Madison physics professor Ke Fang. “For example, a neutron star offers a magnetic field that is trillions of times stronger than on the Earth, and magnetars offer a field that is hundreds of trillions of time stronger. They are natural places to test many fundamental physics theories.”
Fang and UW–Madison astronomy and physics professor Ellen Zweibel are part of a new research collaboration announced August 21 by the Simons Foundation. The Simons Collaboration on Extreme Electrodynamics of Compact Sources (SCEECS) will study how electrodynamics — the interaction of electric currents and magnetic fields — behave in extreme environments in the distant universe using a combination of theory, simulation, and observation.
SCEECS has six main research questions, three centered on understanding electrodynamics in neutron stars and three centered in black holes. Each question pairs at least one senior-level investigator with an early-career co-investigator. Zweibel serves as the lead investigator on her black hole question, and she is paired with Richard Anantua at UT-San Antonio. Fang is co-investigator on a neutron star question, and she is paired with Anatoly Spitkovsky at Princeton.
The neutron star “labs” that Fang is using are amongst the most dense stars in the universe — as small as 10 kilometers in diameter and with densities a million billion times that of water. High energy particles streaming from neutron stars are detectable on Earth, but they tend to be significantly altered by the time they make it here.
“How do those particles survive, in the sense that these extreme energy particles would interact with the surrounding media and produce secondary particles, and how do these interactions play a role in converting what you see on Earth?” Fang’s research asks. “There are also several major questions revealed by recent observations, such as extended TeV gamma-ray halos around neutron stars that are completely new phenomena. We would like to go from first principle physics to understand these phenomena.”
Zweibel’s research will use the extreme environment of spinning black holes, where the electromagnetic field has recently been identified as a major factor in accretion flows, or the movement of gases into the dense center. Her question asks how these accretion flows contribute to magnetizing black holes to form relativistic jets, or powerful emissions of radiation and high-energy particles.
“Accretion disks, their magnetic fields, and their magnetized jets are found throughout the Universe. They play essential roles in star formation, in the evolution of double, or binary stars, and in many other astrophysical settings,” Zweibel says. “The magnetized accretion disks surrounding black holes are by far the most extreme, and test our theories to the limits. Remarkably, we can circle back to laboratory plasma experiments, including some right here at UW, to study magnetized disks and jets as well.”
SCEECS is housed at Stanford University and includes researchers from 14 other US and international universities. UW–Madison and Columbia University are the only universities that have more than one investigator in the collaboration. Most of the funding will be used to support investigators, postdoctoral fellows, and graduate students.
The collaboration plans to host an in-person kick-off in October at Stanford with regular virtual meetings throughout the year. Those meetings will be a place where everyone involved in the research, including students, postdocs, and faculty, can provide updates and seek feedback. Larger-scale collaborations such as this one are nothing new to physicists, but those groups are almost always made up of experimental physicists.
“It’s rare for theorists to be in a larger collaboration because we’re usually working alone or in a small group,” Fang says. “This program is exciting because it collects leading theorists in the field from many different institutions and provides a network for us to collaborate with each other.”
The Simons Foundation’s mission is to advance the frontiers of research in mathematics and the basic sciences. The Foundation makes grants in four areas, including Mathematics and Physical Sciences, through which this collaboration is supported.
Federal grants to 2 Wisconsin startups highlight UW’s leading role in fusion energy
A pair of startups with University of Wisconsin–Madison roots — one spun out of Department of Physics technology — have received large federal grants to support their efforts to develop clean energy through fusion.
Realta Fusion and Type One Energy Group, both based in the Madison area, were two of eight ventures from across the nation that the U.S. Department of Energy selected for grants worth millions of dollars to support research and development of fusion energy technologies. Earth-based fusion energy, which seeks to mimic the nuclear fusion that powers the stars, could someday provide a source of clean, safe and virtually limitless power and heat.
UW–Madison has a reputation as one of the leading places in the world for plasma physics and fusion research, and local companies are emerging from that knowledge base. Match that to the deep expertise in manufacturing in the state and we have the key ingredients to make Wisconsin the global hub for fusion. — Physics professor and Realta Fusion Chief Scientific Officer Cary Forest
One-quarter of the companies chosen for this federal investment are based in Wisconsin, reflecting UW–Madison’s leading role in fusion research to generate renewable and reliable energy as the United States strives to reduce its reliance on fossil fuels.
“UW–Madison is creating valuable partnerships in this potentially transformative option for meeting the energy needs of future generations,” says Amy Wendt, associate vice chancellor for research in the physical sciences. “With growth in innovative public-private partnerships for fusion research, we are looking forward to building on UW’s strong history and growing global leadership in the science and technology that will enable the realization of fusion power.”
Both Realta Fusion and Type One Energy Group are pursuing fusion energy based on technologies pioneered by researchers at UW–Madison.
Realta is working to develop fusion energy and heat for industrial applications via a compact but powerful magnetic mirror as an early step toward larger-scale fusion applications. The company was spun out of a federally funded research project housed in the Department of Physics and led by physics professor Cary Forest.
“Wisconsin is extremely well positioned to lead in the commercialization of fusion,” says Forest, who co-founded Realta and serves as its chief science officer.