The visit follows a partnership announcement between the Public Service Commission and UW's Department of Nuclear Engineering and Engineering Physics to study nuclear energy opportunities in the state.
Read the full article at: https://news.wisc.edu/governor-gets-firsthand-look-at-future-of-nuclear-energy-at-uw-madison/Plasma
Vladimir Zhdankin earns DOE Early Career award
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.”
With major U.S. investment, UW-Madison leads effort to advance abundant fusion energy for all
Highlights from APS DPP
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.
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.
“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.
UW physicists use Purdue supercomputer to challenge traditional turbulence theory for space and climate modeling
Read the full article at:
https://www.rcac.purdue.edu/news/6956
UW-Madison, Japan’s National Institute for Fusion Science strengthen research partnership
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.