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Department of Engineering Physics Nuclear Engineering / Engineering Physics / Engineering Mechanics & Astronautics

SPRING/SUMMER 2002

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Chris Hegna

Chris Hegna (17K JPG)

In Chris Hegna's world, plasmas — the high-energy ionized gases that fuel nuclear fusion experiments — behave the way they're supposed to.

Often, it's only in theory. "Basically we're in the business of providing theoretical understanding and guidance for plasmas as applied to magnetic fusion energy science," he says.

It's what Hegna does best, and after more than 10 years as a scientist with the Center for Plasma Theory and Computation, he joined the department as an associate professor last fall.

In the last decade, most of Hegna's research efforts have focused on very large-scale instabilities in plasmas. "You try to keep the hot plasma away from the walls by using magnetic confinement," explains Hegna. "Now, the plasma is very tricky. It figures out ways to work around it."

When that happens, the plasma deforms. And Hegna and other center researchers step in to model the problem mathematically. In one case, called a kink mode, the plasma "leans" into the reactor wall; in another, tiny filaments of plasma form "islands" within the whole plasma. If the islands get too big, they deplete the plasma of its energy. With Professor Jim Callen, the center's director, Hegna has worked extensively to describe the latter instability and apply the findings to the world's largest high-temperature tokamak experiments, including those in California, Japan and the United Kingdom. "It really is an instability that is very prominent now in lots of large tokamaks, and so we worry about this for all future experiments," he says. "Ultimately, fusion reactors may have to worry about these sorts of things."

Like his colleague, Assistant Professor Carl Sovinec, Hegna lends his expertise to the university's fusion experiments: the department's Pegasus toroidal experiment, the physics department's Madison Symmetric Torus (MST), and the Helically Symmetric Experiment (HSX), housed in electrical and computer engineering. In both the MST and HSX, instabilities pose the greatest challenge. But while he studies the physics and effects related to experimenting with higher temperature plasmas in the MST, Hegna examines how the nonsymmetrical HSX confines plasma with magnetic fields generated by external coils. One instability in particular, called the ballooning mode, may limit the HSX, he says. "Ballooning" occurs when pressure in the plasma causes parts of it to creep in balloonlike fingers from the hot core to the edge. "So understanding the ballooning mode in three-dimensional geometry is really kind of a research area that no one's even thought about too much," he says. "That's one of the things we're pursuing big time, right here."

A DeForest, Wisconsin, native, Hegna earned bachelor's degrees from UW-Madison in 1986 in applied mathematics, engineering and physics. He holds master's and PhD degrees in applied physics from Columbia University, and has spent time at the National Institute for Fusion Science in Nagoya, Japan, and at the United Kingdom Atomic Energy Authority's Culham Laboratories, host to Europe's flagship fusion project, in Abingdon, England.

On campus, he welcomes the opportunity to work with three diverse plasma experiments staffed with everyone from faculty and scientists to postdoctoral and undergraduate students. "I interact with a lot of them and it's really quite fun and entertaining," says Hegna. "It's definitely a great atmosphere."

Carl Sovinec

Carl Sovinec (28K JPG)

Given one of Carl Sovinec's magnetofluid simulations, a 200-computer network of the most powerful personal computers might labor nonstop for days before generating a solution. It's a testament both to the complexity of the simulation and to the amount of computational muscle available today.

Sovinec, who joined the faculty as an assistant professor last summer, conducts computer simulations that model the electromagnetic activity in magnetic-confinement fusion experiments. On campus, his work could benefit researchers who work with three such devices, which confine the plasma — the fuel that drives fusion energy production — with a magnetic field.

So far, he has worked most extensively with the Department of Physics' toroidal reversed-field pinch device, the Madison Symmetric Torus, or MST. A torus (shaped somewhat like a giant steel doughnut), the MST produces a magnetic field that travels in one direction around the torus inside the plasma and in the opposite direction outside. "The fusion community found that you can produce good plasmas by doing that," says Sovinec. "The central theme of the MST research is using the knowledge that we've gained on these configurations to improve the confinement — to make it more competitive. And simulations are playing a large role."

His simulations also could help researchers better understand Pegasus, a tokamak plasma-confinement experiment built and run by engineering physics students and faculty. Like the MST, Pegasus is torus-shaped. However, it requires a much larger magnetic field to operate properly. "I'm trying to get more of my students involved in doing simulations for Pegasus, says Sovinec. "There is electromagnetic activity in the experiment that's not well understood, and it's limiting the performance of the device."

Because of its unusual shape, Sovinec hasn't yet tried running simulations of the Helically Symmetric Experiment (HSX) housed in the Department of Electrical and Computer Engineering. Whereas Pegasus and the MST have relatively symmetric magnetic field structures, that same structure in the HSX is called quasi-helically symmetric. In other words, it's a simulation-code programmer's geometric nightmare.

To conduct simulations, Sovinec bids for computing time on an IBM SP3 supercomputer, which has more than 2,000 processors, or a Cray T3E with 500 processors, at the National Energy Research Scientific Computing Center in Berkeley, California. However, he and Assistant Professor Paul Wilson recently purchased about 36 Linux nodes to establish their own computing cluster on campus. "We should be able to do decent-sized calculations right here," he says.

Already establishing himself as an expert in the field, Sovinec is collaborating on a large-scale computing initiative with funding from the Department of Energy's Office of Science. In addition, he is hoping to receive funding to research electromagnetic activity in the presence of strong inductive effects, and is part of a proposal that would establish a National Science Foundation plasma research center on campus. "The idea is to have a center that's going to establish collaboration between laboratory plasma physicists and astrophysical plasma physicists so that we can share findings and help speed the progress of plasma physics both ways," he says.

Sovinec, who has 10 years in the U.S. Air Force (including four years as an undergraduate at the Air Force Academy) to his credit, received his PhD in physics from UW-Madison in 1995. Before his faculty position here, he worked at Los Alamos National Laboratory, New Mexico, as a postdoctoral student and later as a researcher.

Although faculty life presents a new twist on time formerly filled with research, Sovinec is enthusiastic about his new job. "I'm enjoying working with students," he says. "And engineering physics is a great department with an outstanding collegial atmosphere."

Teaching is learning.
Learning is teaching.
Effective teaching leads to effective learning.
Effective learning leads to effective teaching.

Paul P.H. Wilson

Paul P.H. Wilson (16K JPG)

More than anything else, this philosophy expresses the importance of teamwork in achieving effective teaching and learning," writes Paul Wilson on his website. "The unique abilities, learning styles and experiences each member contributes to the team enhance the team's ability to achieve its goals. My contribution is to form the foundation for a positive learning environment that encourages the team members to be relaxed and at ease while it challenges them to think and to grow. This combination ensures that both learning and teaching are productive, engaging and fun.

Wilson, whose passion for teaching almost led him to become a high school teacher, joined the department last July as an assistant professor. "Since I started graduate school, I've wanted to get into an academic career, mostly because I'm interested in teaching as well as research," he says of his choice.

After earning a bachelor's degree in engineering science from the University of Toronto, Wilson began master's and then PhD work in nuclear engineering at UW-Madison. "I was focused on fusion systems and my work here was developing a code to be used primarily in analyzing potential fusion reactors," he says. In addition to his degrees here, Wilson completed a PhD at Technical University of Karlsruhe, Germany. "In Germany I used that same program to analyze an accelerator-based irradiation facility," he says.

Now the core of Wilson's research is something he calls isotopic inventory analysis, or computationally simulating how isotopes in a nuclear system change over the lifetime of the system. He hopes to apply the technique both to activation in fusion, and burn-up and depletion in fission. "The ability to merge the two, I think, is important for studying future nuclear fuel cycles," he says.

His long-term goal is to develop one piece of software that can analyze both. In the meantime, however, his work will help the nuclear community determine whether materials from fusion reactors are radioactive when it's time to dismantle the reactors and dispose of or sell the materials. In addition, knowing the levels of radiation in a facility will help reactor personnel decide whether humans or robots will do maintenance. In the fission world, Wilson's calculations help characterize nuclear waste. "They help you track the material very carefully, which is an important input to doing analysis for nuclear proliferation," Wilson says.

Wilson, who was hired in the energy systems and policy cluster of the university's cluster-hiring initiative, marries the technical side of his research with the policy aspects. Among his activities, he is involved in the Department of Energy's Generation IV research and development roadmap team, which is plotting the department's next 30 years of reactor R&D.

He also is a founding member of North American Young Generation in Nuclear (NA-YGN), a professional organization for people primarily under age 35 in the nuclear industry. Just three years old, the organization boasts about 425 members from the United States, Mexico and Canada. "One of the things that sets it apart is that the young generation grew up in the age of environmentalism and still chose careers in nuclear science and technology and had that passion for it in the context of everything else that's going on in the world," says Wilson. "I think it makes the young generation more able to communicate with the public and to be constructive in changing people's opinions about nuclear science and technology."

 

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Date last modified: Wednesday, 22-May-2002 17:26:00 CDT
Date created: 22-May-2002