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Focus on new faculty: Benedikt Geiger, studying plasma physics for fusion energy

Written By: Adam Malecek


It’s an exciting time for fusion research at the University of Wisconsin-Madison College of Engineering, which already has an international reputation for leadership in fusion science and plasma physics. For one, major upgrades to the college’s Helically Symmetric eXperiment, or HSX, will take that one-of-a-kind fusion experiment to new heights.

Adding to this “fusion energy” is Benedikt Geiger, who joined the Department of Engineering Physics as an assistant professor in spring 2019.

Motivated by the ultimate goal of achieving fusion energy, Geiger’s research focuses on high-temperature plasma physics. Fusion, the process that powers our sun, holds potential for providing an abundant source of environmentally friendly energy.

But first a number of challenges need to be overcome. One of these big challenges involves finding ways to limit and control turbulence in the plasma as it’s magnetically confined in fusion devices.

In a fusion device, plasma fluctuations will develop turbulence, which can cause particles and energy to flow out of the plasma. That’s a problem because such strong transport will reduce the energy confinement of the fusion experiment and limit the temperatures that can be achieved in the fusion plasma.

“In my research I’m trying to gain a better understanding of turbulent transport in fusion devices in order to find ways to reduce it, which will ultimately help improve the feasibility of fusion energy,” Geiger says.

After earning his master’s degree and PhD in physics from Ludwig Maximilians University in Munich, Germany, Geiger was a postdoctoral scholar at the Max-Planck Institute for plasma physics in Garching, Germany, and then joined the institute as a senior staff scientist. He went on to lead a young investigators group there and conducted experiments at the Wendelstein 7-X stellarator before coming to UW-Madison.

Earlier in his career, Geiger’s research focused on tokamaks, the most prevalent and well-developed type of fusion-research devices. He now primarily studies stellarators, which are widely viewed as the main alternative to tokamaks for fusion reactors.

“I’m excited by stellarator research because these devices haven’t been excessively studied for long and there’s still a lot to explore,” he says. “With stellarators, we can work with smaller, less expensive devices and do interesting physics. And we have ideas on how to maybe get stellarators to perform better than tokamaks in terms of transport properties.”

At UW-Madison, Geiger will be heavily involved in research with the HSX stellarator, which is housed in the Department of Electrical and Computer Engineering. His experimental research involves injecting trace particles into the plasma and then following their movement.

“By looking at the trace particles’ movement from the plasma edge to the core, and measuring how long that takes, you can get really important information on the transport processes,” he says. “In order to explain the behavior of the plasma, we first need to measure the behavior, and one key measurement we can take involves the particle transport.”

In addition, Geiger will be contributing to HSX upgrades by implementing a new heating system that he brought over from Germany. “With this upgrade, we’ll be able to operate HSX with 10 times higher heating power, which will allow the machine to operate in a completely new parameter space and really give a boost to our fusion research at UW-Madison.”

Geiger says the EP department’s outstanding reputation in plasma physics and fusion science attracted him, as well as the resources available for plasma research at UW-Madison overall.

“It’s not only the EP department, but also the ECE department and the physics department, which together have four plasma physics experiments at the university,” he says. “UW-Madison has a really great community with a lot of brilliant professors and talented students, who have shown they can build their own devices and really make an impact. There’s a lot of excellent work happening here that drew my attention.”

As he conducts research at UW-Madison, Geiger will maintain his ties to the W7-X experiment, providing his students with the opportunity to participate in experimental activities on-site at the massive German stellarator.

In fall 2019, Geiger is teaching Fundamentals of Nuclear Engineering. He’s also looking forward to teaching a plasma lab in spring 2020 and engaging students with hands-on projects.