Princeton Plasma Physics Laboratory (PPPL) is the U.S. Department of Energy national laboratory devoted to 📝plasma physics and 📝fusion energy, sited on Princeton University's Forrestal Campus in Plainsboro Township, New Jersey, and managed for the DOE by Princeton University.
Magnetic fusion research began at Princeton in 1951 under the classified Cold War code name Project Matterhorn, after the astronomer Lyman Spitzer Jr. proposed confining a plasma inside a figure-eight tube whose external coils twist the magnetic field — the 📝stellarator, the first alternative to the 📝Tokamak line. After declassification the program was renamed PPPL in 1961. From 1982 to 1997 the laboratory operated 📝TFTR, which ran the first sustained 📝deuterium-📝tritium campaign in a tokamak and produced the first direct measurements of 📝alpha heating.
The present flagship is 📝NSTX-U, a 📝spherical tokamak designed for 2 MA of 📝plasma current at about 1 📝tesla with up to 12 MW of 📝neutral beam injection (NBI). It ran ten weeks of research operations in 2016 before a turn-to-turn fault in an inner 📝poloidal field coil forced a shutdown; the recovery project replaced all three inner coil pairs, and the rebuilt central magnet bundle arrived at the laboratory in June 2026. Meanwhile PPPL returned to its origins with MUSE, its first stellarator in fifty years, which reached first plasma in February 2023 using off-the-shelf permanent magnets embedded in a 3D-printed shell rather than shaped electromagnets.
PPPL's theory program supplies codes much of the field runs on, including the TRANSP transport analysis suite and the extended-📝MHD code M3D-C1, and the laboratory jointly leads 📝INFUSE with Oak Ridge. A 2024 Nuclear Fusion study led by PPPL's Andreas Kleiner used M3D-C1 to size 📝SPARC's 📝massive gas injection system, with CFS co-authors 📝Ryan Sweeney and 📝Matt Reinke; it concluded that six valves, three above the midplane and three below, give the best 📝disruption protection, and SPARC's design adopted that arrangement (10.1088/1741-4326/ad9ec4).