A compact toroidal plasma configuration with both toroidal and poloidal magnetic fields generated entirely by internal plasma currents — requiring no external toroidal field coils.
ReviewedLast reviewed: 9 Aug 2026·Category: Concepts & Physics
Concept
A spheromak is a compact toroid in which the magnetic field is generated almost entirely by currents flowing within the plasma itself. Unlike a tokamak (which requires large external toroidal field coils), a spheromak’s toroidal and poloidal fields are self-generated through a process of magnetic self-organisation called Taylor relaxation.[1]
Taylor state: The spheromak relaxes toward a minimum-energy state (the Taylor state) in which the current density is everywhere parallel to the magnetic field: ∇×B = λB. This self-organised equilibrium is remarkably robust — the plasma spontaneously reconstructs it even after large perturbations.
History
Spheromak research was active at LLNL (the SSPX experiment), the University of Washington, and Los Alamos in the 1980s–2000s. SSPX demonstrated electron temperatures above 0.5 keV and confinement times consistent with tokamak scaling laws when magnetic fluctuations were reduced. However, dedicated funding declined as tokamaks dominated.[2]
Advantages and Challenges
Spheromaks require no expensive external toroidal field magnets and can be formed by simple pulsed circuits, making them potentially inexpensive. However, the turbulent dynamo that sustains the spheromak also degrades confinement. Achieving reactor-grade performance requires operating in low-fluctuation regimes, which has proven difficult to sustain.[3]
Sources
Bellan, P.M. Spheromaks: A Practical Application of Magnetohydrodynamic Dynamos and Plasma Self-Organization. Imperial College Press, 2000.
McLean, H.S. et al. "Suppression of MHD fluctuations leading to improved confinement in SSPX." Physical Review Letters, 88, 125004, 2002.
Taylor, J.B. "Relaxation of toroidal plasma and generation of reverse magnetic fields." Physical Review Letters, 33, 1139, 1974.