Princeton physicist whose work on stellarator optimization produced the quasi-axisymmetric concept — bridging tokamak-like confinement with stellarator steady-state advantages — and who co-founded Thea Energy to commercialize the approach.
Michael Zarnstorff is a physicist at the Princeton Plasma Physics Laboratory (PPPL) who has spent more than three decades advancing the science of toroidal plasma confinement. He has served as deputy director for research at PPPL and has held leadership roles on multiple major experiments including the National Compact Stellarator Experiment (NCSX) and the National Spherical Torus Experiment (NSTX).[1]
Zarnstorff earned his Ph.D. from Princeton University working on the Tokamak Fusion Test Reactor (TFTR), where he made early measurements of bootstrap current — the self-generated plasma current that reduces the need for external current drive and is now central to advanced tokamak and stellarator design. This early work on transport and self-organization set the stage for his later contributions to stellarator physics.
Zarnstorff's most influential contribution has been in the theory and design of quasi-symmetric stellarators. Traditional stellarators confine plasma using external coils alone (eliminating the need for plasma current), but historically suffered from poor particle confinement compared to tokamaks. Zarnstorff and collaborators showed that by carefully shaping the magnetic field to approximate an underlying symmetry — quasi-axisymmetry or quasi-helical symmetry — stellarators could achieve tokamak-like confinement while retaining their inherent steady-state capability.[2]
He was the principal physicist behind NCSX, a compact quasi-axisymmetric stellarator designed to test these optimization principles experimentally at PPPL. Although NCSX was cancelled in 2008 due to construction cost overruns, the physics design validated by Zarnstorff's team has remained the intellectual foundation for subsequent quasi-symmetric stellarator concepts worldwide.
In 2022, Zarnstorff co-founded Thea Energy (originally Princeton Stellarators), a private fusion company that aims to build a quasi-axisymmetric stellarator power plant using arrays of simple planar coils rather than the complex shaped coils traditionally required. The planar-coil approach, enabled by advances in computational optimization and high-temperature superconducting (HTS) magnets, dramatically simplifies manufacturing while maintaining the optimized magnetic geometry.[3]
Beyond stellarator physics, Zarnstorff has contributed to understanding plasma rotation, internal transport barriers, and the role of magnetic field errors in tokamak performance. He is a fellow of the American Physical Society and has received the Kaul Foundation Prize for Excellence in Plasma Physics Research. His ongoing work at both PPPL and Thea Energy positions him at the intersection of public fusion science and private commercialization.