Physicist Michael Zarnstorff has retired after 40 years at the U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL) — a career that included leading research on the famous, record-setting Tokamak Fusion Test Reactor (TFTR), serving as deputy director for research and chief science officer for many years and helping to design stellarators, most recently with permanent magnets. And he’s not done yet. 

The award-winning scientist plans to continue his research as a senior research physicist, the Lab’s title for emeritus scientists. He said he is grateful for his four decades at PPPL. “It’s been a great joy and a great experience,” Zarnstorff said. “One of the best parts about working at a national laboratory like PPPL is there are so many research opportunities. It’s a matter of choosing what you want, and that’s a delightful context to be in.” 

Steve Cowley, the Laboratory’s director, said Zarnstorff has made numerous contributions to plasma physics and PPPL. “I’m grateful to Mike for his amazing scientific insights, leadership, creativity and collegiality,” Cowley said. “I’m glad he plans to continue his research pursuits after he retires.” 

Zarnstorff has made numerous contributions to the Laboratory during his eclectic career, most recently on the development of the permanent magnet MUSE stellarator. He is also well known at PPPL for bicycling to work from Princeton, New Jersey, most days and for wearing sandals all year long. 

Zarnstorff was interested in science from an early age. As an undergraduate at the University of Wisconsin-Madison, he majored in math, computer science and physics. He ran his own software and hardware company with a group of friends with clients located as far away as the Netherlands. He went on to earn his doctoral degree in physics at the same university.
 

A major discovery early in his career 

He was already a star when he arrived at PPPL in 1984, having discovered the “bootstrap current” with Stewart Prager, his professor at the time. Prager later became director of the Laboratory, and the two received the American Physical Society’s 2008 John Dawson Award for Excellence in Plasma Physics Research for the discovery. Their research showed that the plasma itself generates the magnetic field in a plasma. The bootstrap current combines with the magnetic field in the plasma’s core to produce the magnetic field that confines and stabilizes the plasma in fusion devices. 

As an early career physicist at PPPL in the 1980s and ’90s, Zarnstorff was one of the leaders of experiments using a deuterium-tritium fuel mixture on the TFTR, the groundbreaking fusion experiment that broke several world records for fusion power, including a record 10.7 million watts of fusion power in 1994. He led teams that developed and analyzed new plasma confinement regimes to produce high temperature, high pressure plasma used for the fusion experiments. “I was relatively young at the time, so it was a formative experience as well as an intense experience,” Zarnstorff said.

PPPL named Zarnstorff a distinguished research fellow in 1995 for “excellence in the design, execution and analysis of fusion experiments.” Ronald Davidson, then the director of the Laboratory, said Zarnstorff “has been a major intellectual force in the design, execution and analysis of experiments on TFTR.” 

Zarnstorff was one of the leading researchers who helped design the National Compact Stellarator Experiment, a fusion device that contains the plasma within twisty coils rather than the doughnut shape of tokamaks. The experiment was never finished due to cost and other factors, but it was among the first to be designed and built with the aid of computers.

A transformative leader

In 2009, Zarnstorff became deputy director for research at PPPL under the leadership of Prager, alongside then deputy director for operations Adam Cohen. He remained in that position for 10 years. During that time, he helped lead an effort to broaden the Laboratory’s mission to include exascale computing and to strengthen research initiatives in low temperature and high-energy density plasmas. He also helped establish a strong postdoctoral fellowship program and strengthened the Lab’s collaborations with fusion experiments in Japan and Germany. 

“Having a hand setting the direction of the Laboratory, helping guide the ship and also guiding the development of our staff was a pleasure,” Zarnstorff said.

Zarnstorff was succeeded by Jonathan Menard, the current deputy director for research, and he remained at PPPL as a chief scientist. Over the past few years, Zarnstorff has worked with numerous graduate students and plans to continue doing so. One recent project he worked on with his students was MUSE, a device that uses the same kind of magnets that hold children’s artwork on refrigerator doors. The goal of the project is to demonstrate that optimized stellarators can be made using simple construction techniques and materials.

Collaborations with scientists around the world 

Another aspect of his job at PPPL Zarnstorff enjoyed and plans to continue is collaborating with scientists worldwide on various fusion experiments. He has spent summers in Germany working on the Wendelstein 7-X stellarator, the JT-60SA in Japan, the Joint European Torus (JET) in the U.K., the DIII-D National Fusion Facility in San Diego and numerous other experiments. 

Zarnstorff has plenty of ideas for research projects during his retirement, including returning to his roots and exploring some of the research data from TFTR. While researchers found ways to confine plasma effectively, he said, they never understood why they worked so well. “We can use the evolving computational tools we have now to analyze TFTR data that has never been analyzed,” Zarnstorff said.

He plans to spend more time with his wife, Sally, a retired computer scientist, at their home in Princeton, New Jersey, and to travel more. The couple has an adult son, Jonathan, a computer scientist who lives in Boston.

Zarnstorff looks forward to continuing to work with graduate students and collaborating with many of his colleagues. “I’ve had no end of enjoyment — it’s been a real pleasure the entire time,” he said. “Not only was I interested in solving all these problems, but I had colleagues to work with, colleagues to team up with and take on projects that you can’t just do by yourself. That is hugely important when you’re taking on really big problems. That’s another benefit and another key aspect of being at a national lab.”