Zachary S. Hartwig is a 🏷️#physicist and associate professor of nuclear science and engineering at MIT, with a co-appointment at the 📝MIT Plasma Science and Fusion Center, and a co-founder of 📝Commonwealth Fusion Systems. He served as the MIT principal investigator for the Toroidal Field Model Coil program, the joint MIT–CFS effort that built and tested the 📝high-temperature superconducting (HTS) magnet on which 📝SPARC's design depends.

Hartwig led the TFMC team from 2019 through the end of 2021. On September 5, 2021 the coil reached a peak field on conductor in excess of 20 📝tesla — the strongest field of its kind built for fusion, and the result that established a compact high-field 📝tokamak as an engineering proposition rather than a projection. He is first author of the program's technical record, "The SPARC Toroidal Field Model Coil Program," and of the 2020 paper describing @VIPER, the high-current 📝REBCO cable developed at MIT and CFS for fusion magnet windings. He received the Fusion Power Associates Excellence in Fusion Engineering Award in 2022.