A compact toroidal plasma confined by its own currents with no central column or toroidal field coils — the approach pursued by TAE Technologies and Helion Energy for commercial fusion.
A field-reversed configuration is a compact toroidal plasma in which the magnetic field is generated primarily by plasma currents rather than external coils. Unlike a tokamak, an FRC has no toroidal magnetic field and no central column — the plasma forms a self-organized, elongated “cigar-shaped” plasmoid confined inside a simple solenoidal magnet.[1]
FRCs are formed by field reversal: an externally applied solenoidal field is reversed, trapping plasma in a closed magnetic configuration. The resulting plasmoid has primarily poloidal magnetic field, with no toroidal field. This makes FRCs vulnerable to the n = 1 tilt instability at small size, but at large s-parameter (number of ion gyroradii across the separatrix) they become stable.[2]
TAE Technologies has operated the largest FRC experiments (C-2W/Norman, now Copernicus) and targets p-11B (proton-boron) fusion. Helion Energy uses colliding FRC plasmoids to achieve fusion conditions and compress the merged FRC to directly extract electricity. Both companies have raised over $1 billion.[3]