Plasma

Welcome Prof. Qian!

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Photo of Tony QianAfter completing his PhD at Princeton University, Dr. Qian arrived at UW–Madison as a recipient of the Anna Julia Cooper fellowship, where he collaborated with professors Jorge and Forest. He joined the department as an assistant professor in August 2026.

Please give an overview of your research

My research investigates the physics of plasmas and nuclear fusion. I am an experimental physicist who builds fusion machines. In the past, I have worked with the Levitated Dipole Experiment, the Princeton Field Reverse Configuration, and the C2-W experiment at Tri Alpha Energy. More recently, I helped build the permanent magnet stellarator MUSE and the HTS axisymmetric mirror WHAM.

I am interested in combining mirrors and stellarators in a new way. Stellarators have the best confinement at long pulse, and mirrors have the simplest geometry for magnetic confinement. Is there a way to combine them? If so, we may be able to design a new type of fusion machine that has both high energy confinement (the ratio of plasma energy over power input) and high magnetic efficiency (beta, the ratio of plasma pressure to magnetic pressure that measures magnetic efficiency), for the first time. My group is investigating the experimental and theoretical physics of this path.

What are one or two main projects you’ll have your group focus on first?

We are building a new experiment at UW–Madison, SLAM (Stellarators-Linking-Axisymmetric-Mirrors), which involves several projects. On the lab side, we are developing microwave heating systems to create high energy electrons, and radiofrequency heating to create high density plasma. We are also developing plasma diagnostics using electrodes, magnetic sensors, and lasers; and we are assembling power supplies, electromagnetic coils, and permanent magnets for plasma shaping. On the theory side, our projects include stellarator optimization, MHD equilibrium and stability, PIC simulation of a magnetic mirror embedded in a closed-field-line torus, and neutronics simulations for fusion blankets and coil shields.

What attracted you to Madison and the university?

Madison has more plasma experiments than any city in North America.

Today the diverse family of experiments includes: MST (Madison Symmetric Torus) – one of the world’s largest Reversed-Field-Pinches, Pegasus – the largest operating spherical tokamak in the United States, WHAM – the fusion experiment with the highest magnetic field (and first to use HTS with MW plasma heating), and HSX (the world’s first quasisymmetric stellarator, and the largest stellarator in the United States). Madison also has several fascinating non-fusion plasma experiments, including the Big Red Ball astrophysics laboratory and the wake-field-accelerator prototype AWAKE.

Historically, Madison has pioneered physics discovery in octupoles and tandem mirrors and spherical electrostatic plasma traps. This confluence of present and past expertise makes UW the ideal place to test new fusion ideas. Building a lab at UW–Madison is like growing plants in a tropical rain forest. There is a deep and rich topsoil, overflowing with “nutritious” power electronics, plasma diagnostics, and plasma heating hardware – not to mention the wealth of human expertise. But one must not take this for granted. I will work hard to contribute to and continue this tradition at UW–Madison.

What is your favorite element and/or elementary particle?

I would like to describe the neutron, which is neither an element nor an elementary particle.

Neutrons are the glue that hold atomic nuclei together. A world without neutrons would not have any large atomic elements. If the neutron were an element, it would be element zero. But the neutron does not exist alone in nature. While neutrons sit stably in every atom, isolated neutrons decay in about 10 minutes. This process, known as beta-decay, was our first clue to the existence of the mysterious little neutrino (about which, a UW Physics professor recently received the Nobel prize).

Neutrons are the primary product of fusion. Most people want to use neutrons to heat water for energy. I think, if we solve the fusion problem, we can apply it to more creative purposes than boiling water. More imaginative uses for the fusion neutron include: making medicine (pharmaceutical radio-isotopes), recycle nuclear waste (reacting the left overs of fission, while creating energy in the process), and more recently alchemy (transmuting mercury into gold! while producing more neutrons). Of course, one can also use neutrons to do the more traditional thing, generating electric power and heat.

What hobbies and interests do you have?

I love music and language. The stellarator-mirror-hybrid group has a lab piano, which one of our Researchers found (and refurbished) from a UW Music Department sale on SWAP. Anyone in the Physics department is welcome to play! Just come by our lab in 1205 Chamberlin Hall (and please be mindful of others during working hours). It’s a nice break from the lab. In my leisure time, I also enjoy translating poetry and song lyrics across languages.

Unraveling the Mystery of Energetic Particles: How Turbulence Shapes the Universe

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a color map picture that shows calculations

The prevalence of non-thermal, highly energetic particles is one of the most striking features of the universe. Such particles are responsible for some of the most spectacular events in space physics and astrophysics. For instance, these particles are the engines behind the most luminous events in the universe, including Gamma-Ray Bursts and Blazars. They are components of solar flares and coronal mass ejections – outflows of energetic plasma that can damage satellites and disrupt power grids. In laboratory fusion devices, high-energy “runaway electrons” and alpha particles behave like non-thermal populations. Controlling them is vital for achieving fusion energy.

Understanding these particles is a frontier problem in plasma physics and astrophysics. For many decades, scientists have been trying to understand what causes these particles to have so much energy and why they defy the “Maxwell-Boltzmann equilibrium”.

In a recent publication in the Astrophysical Journal Letters, researchers at UW Madison and Los Alamos National Laboratory proposed yet another view on this age-old problem. They analyzed the fact that non-thermal particles often appear in turbulent environments, that is, in systems where the flow of hot ionized gas – plasma – is random. Turbulence, on the other hand, whether it appears in the interstellar medium, Earth’s atmosphere, or a stirred cup of coffee is a rather universal phenomenon. It generates fluid fluctuations, known as “swirling eddies”, whose scales and energies have remarkably universal distributions.

Physicists have long been intrigued by universal laws, which they expect to emerge from theories that explain fundamental physical behavior. These theories can be applied to a variety of systems and environments, often extending well beyond the cases they were first developed for.

In this study, researchers investigated whether the universality observed in the energy distribution of energetic particles is related to the universality of turbulent fluctuations. They focused on the balance of energy between turbulent fluctuations and particles whose gyro-scales (the sizes of their rotational orbits in a magnetic field) are comparable to the scales of these fluctuations. “This energy balance assumption allowed us to analytically predict the particle energy distribution functions,” says Stanislav Boldyrev, one of the study’s authors, “and our predictions aligned with the results of numerical simulations. We may be one step closer to solving the mystery of non-equilibrium particles in space and astrophysical systems.”

He notes, however, that the hypothesis requires further investigation, which may involve both observational and numerical studies. “This study inspires young researchers by highlighting fundamental unsolved problems in plasma dynamics,” continues Boldyrev, “It would not have been possible without the years of hard work by our talented young scientists, which include graduate student Daniel Humphrey and postdoctoral researcher Dr. Cristian Vega, as well as the support from the Department of Energy and the Wisconsin Alumni Research Foundation.”

The figure above shows the electron density in turbulent electron-positron pair plasma.

For more information read the published article.

This work was supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences under award number DE-SC0024362, and by the University of Wisconsin-Madison, Office of the Vice Chancellor for Research, with funding from the Wisconsin Alumni Research Foundation.

Vladimir Zhdankin earns DOE Early Career award

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profile photo of Vladimir Zhdankin
Vladimir Zhdankin (credit: Flatiron Institute)

Congrats to Vladimir Zhdankin, assistant professor of physics, on earning a Department of Energy Early Career award! The five-year award will fund his research on energy and entropy in collisionless, turbulent plasmas. 

Systems in equilibrium are easy to describe, but often the most interesting questions in nature are complex and dynamic. Most plasmas, including astrophysical ones and manmade ones on earth, are not in equilibrium, so they are more difficult to characterize. Zhdankin’s research is working toward a more universal understanding of non-equilibrium plasmas, in the form of mathematical equations that can then be broadly applied. 

“We think that our understanding of plasmas isn’t finished yet, and there are still some basic ingredients in the statistical mechanics which, once we understand better, we’ll have a more predictive framework for how plasmas should behave,” Zhdankin says. 

Collisionless plasmas have a low enough particle density where the particles largely flow without bumping into each other. Instead, their trajectories are controlled by the electric and magnetic field, which leads to a generally chaotic flow, like the rapids of a river. It is that dynamic turbulence that causes these plasmas to be non-equilibrium, leading to interesting, if not straightforward, properties. 

“In these systems, energy is conserved — it has to be,” Zhdankin says. “But we don’t quite have a handle on what’s happening with the entropy. We have reason to believe it’s increasing, consistent with the second law of thermodynamics, but it doesn’t seem to reach a maximum.” 

Zhdankin’s goal is to better understand the energy and entropy in these complex plasmas through “particle-in-cell” simulations, where tens of billions of plasma particles — electrons and protons — are simulated in a small box, then manipulated in various ways.

“We imagine stirring the plasma to make it more turbulent and putting some energy into it, and then we want to see how it heats up and how the particles achieve higher energies,” Zhdankin says. “What if we increase or decrease the size of the box? Make the magnetic field stronger? Make the particles collide a little bit?”

The simulations can then be compared to real-world data, including measurements of the solar wind or laboratory plasmas. An ideal outcome would be obtaining formulae that better describe these complex, turbulent plasmas and can be applied across a broad range of systems, from laboratory experiments to the accretion flows of black holes. 

“And there’s a chance we’re just not going to be able to get something predictive out of this work, if there’s just too big of a landscape of possibilities,” Zhdankin says. “But this topic, I consider it one of the most fundamental ones that could be studied in plasma physics.”

Highlights from APS DPP

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Physics Faculty Attend Major Plasma Physics Conference in Atlanta

By Christopher Woolford, Physics PhD student

Over 200 faculty and students represented the University of Wisconsin–Madison at the annual American Physical Society Division of Plasma Physics (DPP) research conference in Atlanta last October. The APS DPP conference presents an excellent opportunity to learn about the newest and cutting-edge research in plasma physics.

a man stands in front of a poster and give a thumbs-up sign
Prof. Rogerio Jorge presents at the APS DPP conference

Rogerio Jorge, an assistant professor of physics at UW–Madison, presented his work on stellarator optimization alongside several of his students. Stellarators are a type of nuclear fusion reactor that uses twisted magnetic fields to confine fusion reactions.

“The weather was amazing, and the conference is a great opportunity for collaborations,” Jorge says.

This year, the APS DPP conference benefited from attendance by a new generation of plasma physicists that has seemed to have grown in recent years.

“I had not seen so many younger plasma physicists in years at an APS DPP conference,” says Paul Terry, a professor of physics at UW–Madison, attributing the rise in attendance to the influx of private companies interested in nuclear fusion.

Eduardo Neto, a postdoc at UW–Madison working with Jorge, gave a talk on his exciting work on Stellarator optimization. This work was the result of an ongoing collaboration with Proxima Fusion and IST in Lisbon, Portugal.

a man stands to the left of the picture in front of a screen. He is showing a powerpoint presentation to an audience of several dozen people
Eduardo Neto delivers an oral presentation at APS DPP in October.

“The most challenging part of this project was getting a lot of different codes to work together,” Neto says. “Startup companies have a strong interest in preventing tungsten buildup in Stellarators.”

Neto plans to continue his collaborations with Proxima Fusion and explore optimizing other parts of Stellarators such as turbulence. His advice for students interested in Stellarator optimization is to gain broad knowledge of plasma physics and nuclear fusion.

The APS DPP conference will be in November this year in Long Beach, California.

a smiling person stands in front of their scientific poster
Cameron Kuchta presents a poster at APS DPP.
two people stand in front of their scientific poster
Tony Qian and Jonathan Pizzo present a poster at APS DPP.
a man stands in front of a scientific poster
Djin Patch presents a poster at APS DPP.

Rogerio Jorge receives first grant as a professor

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profile photo of Rogerio Jorge
Rogerio Jorge

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

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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. 

MST is shown, it is a donut-shaped metal device that is tens of feet in diameter and has hundreds of wires coming in and out of it
The Madison Symmetric Torus (MST). credit: Noah Hurst

“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
WiPPL scientists were able to experimentally create a stable plasma 10x greater than the Greenwald limit (the dashed horizontal line).
Hurst and colleagues looked into plasma density, trying to destabilize the plasma by puffing in more and more gas. They set the power supply to provide whatever voltage was needed to maintain a steady 50000 amps of current in each plasma (as plasma density increases, it becomes more resistive, and more voltage is needed to keep the current steady). They measured the achieved plasma density with interferometers viewing the plasma along 11 different lines of sight. 

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.”

profile photo of Noah Hurst
Noah Hurst

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).