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August 12, 2021

UW-Madison engineers win DOE grants for fusion energy research at Wendelstein 7-X

Written By: Staff

The U.S. Department of Energy has awarded grants to University of Wisconsin-Madison engineers to lead three research projects at Wendelstein 7-X (W7-X), a major fusion energy facility located in Germany.

The UW-Madison awards are part of $6.4 million in total DOE funding for seven projects announced in June 2021 for research on two international fusion energy stellarator facilities—W7-X and the Large Helical Device (LHD) in Japan.

Oliver Schmitz
Oliver Schmitz

“The award of these three grants is a testimony to the expertise of UW-Madison plasma science faculty to advance the science at these large-scale frontier experiments. This is based in this case on the successful track record of research at the HSX stellarator facility on campus and on dedicated lab experiments that enable our students to obtain leadership roles on such experiments,” says Professor Oliver Schmitz, one of the principal investigators on the grants.

These collaborations enable graduate students, post-docs and scientists from the College of Engineering to explore critical science and technology issues at the frontiers of magnetic fusion research using the unique capabilities of the most advanced overseas research facilities. Fusion energy research seeks to harness the energy that powers the sun and stars as a clean, safe, and abundant source of energy on earth.

Stellarators are fusion facilities that promise steady state, highly-efficient plasma confinement with minimal control needs, all assets for the economic operation of future fusion energy plants. The funded projects at W7-X will continue the major U.S. collaboration with Germany, advance understanding of magnetic confinement, and address research priorities critical to the W7-X mission. The projects were selected by competitive peer review under the DOE Funding Opportunity Announcement for Collaborative Research in Magnetic Fusion Energy Sciences on Long-Pulse International Stellarator Facilities.

Schmitz, Thomas and Suzanne Werner Professor of nuclear engineering and engineering physics at UW-Madison, was awarded $1,279,000 over three years for the project titled, “Three-dimensional Equilibrium Stability and its Impact on Edge Transport and Divertor Performance in W7-X.” The fusion process produces helium ash, which needs to be exhausted from the system to keep the plasma clean for continuous operation. By manipulating the boundary region of the magnetic bottle that is used to confine the fusion plasma, researchers can guide the vast amounts of energy and particles that escape the plasma into specifically armored and designed “divertor” units. The divertor is built to withstand the heat efflux and neutralize the ion flux from the plasma, such that the neutral gas can be pumped away. This aids helium exhaust and allows researchers to control the density of the fusion medium at stable levels. Two PhD students under funding from the previous two grant cycles for this research invented a special diagnostic for these measurements, the Wisconsin In-Situ Penning (WISP) gauge. This measurement system allows unique access to the amounts of helium that are exhausted from the plasma and hence provides essential information to understand how the specially shaped divertor unit can handle the required exhaust of the helium ash in a future fusion reactor. The research of Schmitz’s group for the next three years will focus on expanding this unique measurement capability at the device and aid it by state-of-the-art 3D plasma edge modeling and further dedicated measurements. A total of three graduate students, two post-docs and one professional engineer is involved in the effort.

Benedikt Geiger
Benedikt Geiger

Plasma turbulence is an important loss mechanism for the energy and particles that are confined in a fusion device. Researchers are studying innovative ways to optimize the plasma confinement by reducing turbulent transport, which could enable stellarators to potentially obtain unprecedented levels of energy and particle confinement that would make a stellarator fusion reactor more effective and hence more economic. Two of the projects deal with UW-Madison innovation for turbulent transport studies at W7-X.

Engineering Physics Assistant Professor Benedikt Geiger (PI), Engineering Physics Professor Chris Hegna (co-PI) and Assistant Scientist Ben Faber (co-PI) received $762,000 for their proposal, “Exploring ion heat transport during neutral beam heated plasmas at W7-X.” The researchers will perform studies of turbulent heat transport in W7-X since recent results from W7-X show that the required excellent ion heat confinement is only observed during transient phases and in presence of peaked density profiles.

David Smith
David Smith

Stabilization of this promising regime of enhanced plasma confinement is a central quest of the next campaign at W7-X. Geiger’s team will perform dedicated experiments to steer the level of heat injected into the plasma and the associated heat transport out of the plasma. These experimental results will be compared to recent, state-of-the-art turbulent transport modeling results from Hegna’s research group. The efforts aim to apply new insights into turbulent transport optimization in the highly-shaped stellarator magnetic field configuration gained at UW-Madison to W7-X in order to accelerate the path to fusion energy.

Diagnosing plasma turbulence is a major challenge. Engineering Physics Associate Scientist David Smith (PI) and Senior Scientist George McKee (co-PI) received a $500,000 renewal grant over three years for the project titled, “Implementation and Operation of Beam Emission Spectroscopy at W7-X for 2D Multi-Field Turbulence Measurements.” Beam emission spectroscopy (BES) is an established measurement technique, pioneered by Engineering Physics Emeritus Professor Raymond Fonck, to image plasma turbulence imprinted in the emission of plasma heating beams. To advance the scientific understanding of plasma turbulence in stellarator devices, Smith and McKee, members of the plasma turbulence spectroscopy group in Engineering Physics, will implement a BES diagnostic system at W7-X. Their renewal grant follows a feasibility study that identified a viable diagnostic configuration and estimated diagnostic performance metrics. UW-Madison scientists will work with collaborators in Germany to develop optical views for BES measurements, and custom photodetectors with high sensitivity and high bandwidth will be developed at UW-Madison. This diagnostic development draws from broad campus expertise in the area. Optical design and detector fabrication is being conducted in collaboration with Distinguished Instrument Innovator Kurt Jaehnig (UW-Madison Department of Astronomy) and Distinguished Scientist Daniel Den Hartog (UW-Madison Department of Physics).

These three grants are funding a total of five PhD students, three undergraduate students, two post-doctoral fellows and two scientists. The funds enable transfer of UW-Madison innovation in stellarator science and technology to the large-scale, frontier experiment W7-X. This partnership brings fusion one step closer to reality and involves the UW-Madison College of Engineering graduate research program at the front of this research enterprise.