A New Jersey company developing the Princeton Field-Reversed Configuration reactor, a compact device that uses rotating magnetic fields and radio-frequency heating to confine a small, hot plasma for clean fusion energy and space propulsion.
Princeton Fusion Systems (PFS) was founded to commercialize the Princeton Field-Reversed Configuration (PFRC) concept developed by Samuel Cohen at the Princeton Plasma Physics Laboratory (PPPL). The PFRC is a compact magnetic-confinement device that uses odd-parity rotating magnetic fields (RMF) to both form and heat a field-reversed configuration (FRC) plasma. Cohen's research at PPPL dates to the early 2000s, and PFS was established to carry the concept from laboratory experiment toward a practical reactor.1
The PFRC uses a field-reversed configuration, a toroidal plasma confined by its own internal currents with no material center post or complex external coil array. What distinguishes Cohen's approach is the heating method: odd-parity rotating magnetic fields preferentially heat electrons, which then transfer energy to ions through collisions. This method avoids the large neutral-beam injectors and high-power microwave systems used in tokamaks.
The ultimate fuel target is deuterium-helium-3 (D-3He), an advanced fuel cycle that produces mostly charged particles rather than neutrons. While D-3He has a higher ignition threshold than deuterium-tritium, the PFRC's compact geometry and efficient heating scheme are designed to reach the required temperatures (tens of keV ion temperature) in a device small enough to be economically attractive.3
The reactor concept envisions a cylindrical vacuum vessel only a few meters long, with superconducting coils providing the external magnetic field. Fusion products — primarily 14.7 MeV protons and 3.6 MeV alpha particles from D-3He — would be captured by direct energy conversion, similar in principle to concepts explored for mirror machines.
The PFRC's small size and high specific power make it a candidate for space propulsion. NASA has funded studies of a Direct Fusion Drive (DFD) concept based on the PFRC, in which the fusion exhaust is directed out a magnetic nozzle to produce thrust. Missions studied include rapid transit to Pluto, Jupiter, and Saturn, as well as interstellar-precursor trajectories.4
The PFRC-2 experiment continues at PPPL, incrementally increasing plasma parameters. PFS has received funding from NASA, ARPA-E, and the Department of Energy. The next major step is PFRC-3, which would operate with deuterium fuel (rather than the hydrogen and helium gas used in PFRC-2) and aim to demonstrate fusion-relevant ion temperatures. The path from PFRC-2 to a net-energy reactor remains multi-step, but the concept's compactness and fuel flexibility give it a distinctive position in the fusion landscape.5